COVID-19 Vaccine Studies

Latest COVID-19 Vaccine Research Studies

To date 4 COVID-19 vaccines have been authorised for use in Europe by the EMA.

Since the COVID-19 vaccines have been used in Ireland and worldwide, research has been conducted all over the world that demonstrates the safety and effectiveness of COVID-19 vaccines against the COVID-19 virus.

The graph below shows how Ireland’s COVID-19 vaccination programme, along with public health measures such as social distancing, the wearing of face coverings and tracing and isolating contacts of confirmed cases brought Ireland’s 14-day case incidence down from a peak of 1,426 per 100,000 population January to 107 per 100,000 population in mid-April.


Although there may be recommendations made in external reports - they are for information only. 

Please note that the HSE clinical guidance on COVID-19 vaccines should be referred to for up to date guidance for vaccinators in Ireland.

Investigation of ITP after COVID-19 vaccines

This Scottish study reviews the risk of idiopathic thrombocytopenic purpura (ITP) following vaccination with either a single dose of Vaxzevria® or Comirnaty®. Their estimates suggest a potentially small increased rate of ITP following vaccination with Vaxzevria® around 1.13 in 100,000.

The risk of ITP suggested here is in the context of one study. In comparison COVID-19 itself can cause significant morbidity and mortality. ITP is currently not included as an adverse event for the vaccine in the licensed documentation from the European Medicines Agency. The safety of COVID-19 vaccines is continuously monitored by the EMA, the Health Products Regulatory Authority (HPRA) and NIAC. The benefits from receiving the Vaxzevria vaccine outweigh the risks for adults of all age groups.

Read more here

COVID-19-associated hospitalizations among vaccinated and unvaccinated adults ≥18 years

This paper, available in pre-print and not yet peer-reviewed, compared hospitalisation rates from COVID-19 in the U.S. in vaccinated and unvaccinated individuals.

Population-based hospitalization rates show that unvaccinated adults aged ≥18 years are 17 times more likely to be hospitalized compared with vaccinated adults.

Rates are far higher in unvaccinated persons in all adult age groups, including during a period when the Delta variant was the predominant strain of the SARS-CoV-2 virus.

FP Havers, et al

medRxiv 2021; DOI:

Receipt of mRNA Covid-19 Vaccines in pregnancy: analysis from the Centers for Disease Control and Prevention (CDC) in the US

This analysis from the from the Centers for Disease Control and Prevention (CDC) in the US, reported the rates of miscarriage in women who had received at least one dose of an mRNA COVID-19 vaccine either before conception (30 days before the first day of the last menstrual period through 14 days after) or in pregnancy before 20 weeks of gestation.

They compared rates of miscarriage between 6 and 20 weeks of gestation in women who had received the vaccine, compared with rates in the general population.

The analysis found no difference between women vaccinated with an mRNA vaccine and the rates in the general population. These findings add to the accumulating evidence about the safety of mRNA Covid-19 vaccination in pregnancy.

Read more here

Post-vaccination SARS-CoV-2 infection: risk factors and illness profile in a prospective, observational community-based case-control study

A study, published in The Lancet Infectious Diseases, found that for those who had completed a two course Covid-19 vaccine schedule but went on to develop a Covid-19 infection had a significantly lower risk of developing “long COVID”. Their risk was reduced by almost half (49%).

Hospitalisations were 73% less likely and there were less acute symptoms (31% less) among those fully vaccinated. 

These findings are the first to suggest that although there is evidence of effectiveness for the reduction in Covid-19 infection in those who are fully vaccinated, the risk of long Covid post vaccination infection is also reduced by completing the Covid-19 vaccination schedule.

M Antonelli, et al

medRxiv 2021; DOI:

Clinical Features of Vaccine-Induced Immune Thrombocytopenia and Thrombosis

This prospective cohort study was carried out among 294 patients with suspected vaccine induced thrombocytopenia and thrombosis (VITT) over a three-month period in the UK. There were 170 definite and 50 probable cases if VITT. All patients had received the first dose of the Oxford-AstraZeneca adenoviral vector vaccine. The median number of days following administration of the vaccine to presentation with suspected VITT was 14 days (Range 5-48 days) and the median age was 48 years (Range 18 to 79 years). There was no sex difference and no identifiable medical risk factors. There was a high mortality rate among those with VTTT (22% overall). Mortality was higher among those with lower platelet counts, lower fibrinogen counts, intracranial haemorrhage and cerebral venous sinus thrombosis. Treatment remains uncertain however identification of prognostic markers may help to guide effective management.

Pavord S, et al

N Engl J Med 2021;

Impact of Delta on viral burden and vaccine effectiveness against new SARS-CoV-2 infections in the UK

This large community-based survey of randomly selected households across the UK examined vaccine effectiveness against the COVID-19 Delta variant in those aged 18 years and older. This study found that the effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines is reduced with the Delta variant. Two doses of the Pfizer-BioNTech or Oxford-AstraZeneca vaccine provided the same protection as having previous infection. Those who were vaccinated after infection had more protection than those vaccinated without having had prior infection. Protection was higher among younger age groups and the time between vaccine doses did not affect effectiveness. Compared to Oxford-AstraZeneca vaccines, the Pfizer-BioNTech vaccine has greater initial effectiveness but this declines faster than Oxford-AstraZeneca. A single dose of the Moderna vaccine had similar or greater effectiveness compared to a single dose of the Pfizer-BioNTech or Oxford-AstraZeneca vaccines. For those who were infected with the Delta variant after vaccination, peak levels of virus were similar to those in unvaccinated individuals. Overall, this study found that obtaining two vaccine doses is the most effective way to ensure protection against the COVID-19 Delta variant, however vaccine effectiveness is reduced and peak viral load is higher with the Delta variant.

Read more here

Risk of Myocarditis from COVID-19 Infection in People Under Age 20: A Population-Based Analysis (Pre-print)

This US study examined medical records from 48 healthcare organisations and included patients aged less than 20 years who had a COVID-19 diagnosis between April 2020 and March 2021. The primary outcome was a diagnosis of myocarditis within 90 days of a diagnosis of COVID-19 or a positive COVID-19 test. In total 14,207 patients aged 12-17 years were included in the study. This study found that for males aged 12-17 years, the adjusted rate of myocarditis was 450 per million cases of COVID-19. For females aged 12-17 years, the adjusted rate of myocarditis was 213 cases per million cases of COVID-19. Myocarditis occurred within 5 days in 40% or from 19-82 days in 60%. Two patients were hospitalised and there were no deaths reported. There is a risk of myocarditis associated with receiving an mRNA COVID-19 vaccine. This risk is highest in those aged 12-17 years and is higher in males compared to females. Overall, this study concluded that young males aged 12-17 years infected with the virus are up to 6 times more likely to develop myocarditis as those who receive the vaccine and that young females aged 12-17 years infected with the virus are up to 21 times more likely to develop myocarditis as those who receive the vaccine.

Read more here

Vaccine administration at a higher location than recommended and supraclavicular lymphadenopathy

This case series published in Eurosurveillance, highlights the importance of correct intramuscular injection technique and the administration of the vaccine in the correct site.

The authors report on 20 cases of acute onset of single supraclavicular lymphadenopathy coinciding with administration of a dose of an mRNA vaccine on the same side. While axillary lymphadenopathy had been reported as a recognised adverse reaction following mRNA vaccines, supraclavicular lymphadenopathy had not, and therefore this finding prompted concern amongst recipients and healthcare professionals about other possible cause, including malignancy.

Twelve of the 20 patients in the case series spontaneously reported that the intramuscular injection point was unusually high, and nearly all (17/20) acknowledged a similar perception when they were asked about this specifically (either compared with the previous dose administration or in relation to their theoretical expectation about the exact location of the point of injection).

The authors’ report that if the vaccine was given at a higher location than recommended, the supraclavicular lymph nodes and not the axillary nodes is the most frequent drainage area and therefore this may have resulted in supraclavicular lymphadenopathy.

Land marking the injection site is a crucial step to ensure administration of the vaccine at the correct site of the Deltoid muscle. This has been highlighted in this bulletin, and through training and guidance. See for further details.

Read more here

Safety and Immunogenicity Report from the Com-COV Study – a Single-Blind Randomised Non-Inferiority Trial Comparing Heterologous And Homologous Prime-Boost Schedules with An Adenoviral Vectored and mRNA COVID-19 Vaccine

This study examined whether a mixed vaccine schedule was at least as good as a standard vaccine schedule at producing higher levels of SARS CoV 2 antibodies 28 days after the booster vaccine dose.

463 people who had never received a COVID-19 vaccine previously aged 50 years and over, with no or well-controlled mild-moderate comorbidities.

The findings demonstrate that all the schedules studied (ChAd/BNT, BNT/BNT or BNT/ChAd) induced concentrations of antibodies to SARS CoV 2 at least as high as those induced after a licensed ChAd/ChAd schedule, which is effective in preventing symptomatic COVID-19 when administered at a 4-12 week primeboost interval.

Administering a booster vaccine of either the same or alternative vaccines 28 days after the prime vaccination produced higher levels of SARS CoV 2 antibodies than a single dose of either vaccine alone.

Liu X, et al

The Lancet Published June 25, 2021; DOI:

Importance of the second dose in preventing hospitalisation from the Delta variant

The latest analysis (published as a pre-print) from Public Health England provides further evidence that the vaccines are highly effective against preventing hospitalisation from the Delta variant (B.1.617.2) in England after 2 doses: Comirnaty (Pfizer BioNTech) is 96% effective and Vaxzevria (AstraZeneca) is 92% effective. The vaccines have a similar effectiveness against the Alpha variant (B.1.1.7). Further analysis is underway to understand the impact of vaccination on deaths due to the Delta variant (it is expected to offer a high level of protection similar to
other variants).

Public Health England, June 2021.

Read more here

Immunogenicity and reactogenicity of BNT162b2 booster in ChAdOx1-S-primed participants (CombiVacS): a multicentre, open-label, randomised, controlled, phase 2 trial

This study measured the immunogenicity (the immune response generated from a vaccine) and reactogenicity (reactions that occur after a vaccine) from a mixed vaccine schedule where the prime (first) dose was the Vaxzevria® vaccine, and the second (booster) dose was Comirnaty® COVID-19 vaccine.

They performed a phase 2, open-label, randomised, controlled trial on adults aged 18–60 years, vaccinated with a single dose of Vaxzevria® vaccine 8–12 weeks before screening, and no history of previous SARS-CoV-2 infection.

Participants were randomly assigned (2:1) to receive either Comirnaty® COVID-19 Vaccine (0·3 mL) via a single intramuscular injection (intervention group) or continue observation (control group). The control group did not routinely receive a second dose of Vaxzevria®, but it could be used if requested by the participant or established by local health authorities.

The primary outcome was 14-day immunogenicity, measured by immunoassays for SARS-CoV-2 trimeric spike protein and receptor binding domain (RBD). The safety outcome was 7-day reactogenicity, measured as solicited local and systemic adverse events.

663 (98%) participants (n=441 intervention, n=222 control) completed the study up to day 14. 

In the intervention group, the mean antibody levels increased from 71·46 BAU/mL (95% CI 59·84–85·33) at baseline to 7756·68 BAU/Ml* (7371·53–8161·96) at day 14 (p<0·0001). IgG against the SARS CoV 2 target spike protein increased from 98·40 BAU/mL (95% CI 85·69–112·99) to 3684·87 BAU/mL (3429·87–3958·83).

The mean antibody levels seen in the intervention group for the RBD protein and spike protein were 77 and 36 times greater than those seen in the control group (77·69 (95% CI 59·57–101·32) for the RBD protein and 36·41 (29·31–45·23) for the spike protein IgG).

Reactions were mild (n=1210 [68%]) or moderate (n=530 [30%]), with injection site pain (n=395 [88%]), induration (n=159 [35%]), headache (n=199 [44%]), and myalgia (n=194 [43%]) the most commonly reported adverse events. No serious adverse events were reported.

*BAU/ml: Binding Antibody Units/Millilitre. WHO Standard for assessing antibody response.

Comirnaty® given as a second dose in individuals prime vaccinated with Vaxzevria® induced a robust immune response, with an acceptable and manageable reactogenicity profile.

Borobia AM A et al

The Lancet. VOLUME 398, ISSUE 10295, P121-130, JULY 10, 2021; DOI:

Serum Neutralizing Activity of mRNA-1273 against SARS-CoV-2 Variants

This study examined how effective the SpikeVax® (Moderna) vaccine was against the original “wild-type” SARS CoV 2 virus and against multiple SARS CoV 2 variants of concern.

At day 7 post booster vaccination the concentration of neutralising antibodies against the original “wild-type” SARS CoV 2 virus and against multiple SARS CoV 2 variants of concern of participants were measured

Results showed minimal effects on neutralization titers against B.1.1.7 (Alpha Variant- United Kingdom) compared to D614G (original “wild type” SARS CoV 2 virus).

In contrast, all other variants examined showed decreased neutralization titers compared with D614G, although all remained susceptible to mRNA-1273–elicited serum neutralization.

Reductions in neutralization titers for these variants ranged from a factor of 2.1 to 8.4 compared with D614G.

Among all variants tested, the greatest effect on neutralization was observed for A.VOI.V2 and B.1.351-v3 (Beta Variant- South Africa) (8.0-fold and 8.4-fold reductions compared with D614G, respectively). More modest 3.2- and 2.1-fold reductions were observed for P.1 (Gamma Variant- Brazil) and B.1.617.2 (Delta Variant- India), respectively.

Among VOCs tested, the Spikevax® vaccine produced similar levels of antibody protection against the Alpha variant and the original “wild-type” virus.

All other variants including the B.1.351 (Beta), B.1.617.2 (Delta), and P.1 (Gamma) variants, had lower levels of antibody production compared to D614G ranging from 2.1-fold to 8.4-fold lower levels.

Choi A et al

bioRxiv 2021.06.28.449914; DOI:

SARS-CoV-2 Delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness

This correspondence published in the Lancet compares the demographics, risk of hospitalisation and vaccine effectiveness for the Delta (B.1.617.2) variant when compared with the Alpha (B.1.1.7) variant.

The Delta variant was found to be prevalent across all ages but particularly in children aged 5-9 years and higher socioeconomic groups. The Delta variant was also associated with a significantly increased risk of hospitalisation (nearly twice that compared to the Alpha variant) particularly in those with multiple comorbidities.

Vaccination (two weeks after the second dose) was effective at reducing hospitalisation:

  • Comirnaty (Pfizer/BioNTech) was 92% effective against hospitalisation with the Alpha variant and 79% effective against hospitalisation with the Delta variant.
  • Vaxzevria (AstraZeneca) was 73% effective against hospitalisation with the Alpha variant and 60% effective against hospitalisation with the Delta variant.

Sheikh A, et al

The Lancet Published June 14, 2021; DOI:

Threat Assessment Brief: Implications for the EU/EEA on the spread of the SARS-CoV-2 Delta (B.1.617.2) variant of concern

This report from the European Centre for Disease Prevention and Control (ECDC) highlights the latest evidence on the Delta variant of concern including:

  • The Delta variant is likely 40-60% more transmissible than the Alpha variant (and is likely associated with an increased risk of hospitalisation)
  • Based on modelling data they expect 90% of COVID-19 cases in Europe to be due to the Delta variant by the end of August. They also model the impact of relaxing non-pharmaceutical interventions (such as social distancing , face masks and respiratory/ hand hygiene measures) on case rates, hospitalisations and deaths.

The report also highlights the importance (for both the general population and those at high risk of severe-COVID-19) of completing the full vaccination schedule (for a two dose COVID-19 vaccine regime) to get the best protection against COVID-19 in particular for the Delta variant.

Read more here

NOVAVAX trial results

Novavax’s COVID-19 vaccine (NVX-CoV2373) is currently under a rolling review by the European Medicines Agency (EMA). It is currently not authorised for use in Ireland. It is an adjuvanted protein based (similar to the SARS-CoV-2 spike protein) vaccine. The company has shared pre-published data from its PREVENT-19 phase 3 trial. The study involved nearly 30,000 people from the United States and Mexico. The key results reported include:

  • 90.4% overall efficacy against symptomatic disease
  • 100% protection against moderate and severe disease

Read more here

Safety, reactogenicity, and immunogenicity of homologous and heterologous prime-boost immunisation with ChAdOx1-nCoV19 and BNT162b2: a prospective cohort study

This preprint describes a prospective cohort study that followed up 340 healthcare workers in Germany in one center. The participants either received two doses of Comirnaty 3 weeks apart or one dose of Vaxzevria followed by one dose of Comirnaty (10-12 weeks later).

They reviewed reactogenicity and immunogenicity data. Interim analysis shows the reactogenicity between the heterologous prime-boost vaccine schedule was similar to those who received two doses of the Comirnaty. Good immune response was noted from both vaccine schedules with slightly better T-cell response and higher serum antibody avidity following the heterologous prime-boost vaccine schedule.

Hillus D, et al

medRxiv 2021; DOI:

Community-level evidence for SARS-CoV-2 vaccine protection of unvaccinated individuals

Publication from Israel studies the impact on infection rates in children under the age of 16 (who are unvaccinated) from vaccinating adults with the Pfizer-BioNTech COVID-19 vaccine.

They studied the impact of vaccination on 177 communities with low underlying natural immunity.

They found a correlation between high vaccination rates and lower infection rates later in unvaccinated children within the same community. They estimate that by vaccinating an additional fifth of the population in a community (aged 16-50) this results in nearly a two-fold reduction in positive test fraction within the unvaccinated cohort (children under 16 years of age).

Milman O, et al

Nat Med 2021, DOI;

Antibodies against delta and beta variants of concern after Pfizer BioNTech COVID-19 Vaccine

In this correspondence to the Lancet the authors describe initial analysis from the Legacy Study. The laboratory analysis looks at neutralising antibody activity in participants after one or two doses of the vaccine including against the three variants of concern ( B1.617.2, B.1.351 and B.1.1.7.). After two doses of the vaccine neutralising antibodies were found in the serum of most participants against all the strains examined including against the variants of concern. Although there were lower levels of neutralising antibodies against the delta variant (when compared to the original strain or the alpha variant). In addition the authors reports significantly reduced neutralising antibodies against the beta and delta variants in older participants and over time (since the second dose). Furthermore they notice neutralising antibody activity against the beta and delta variants of concern after only one dose is significantly lower in comparison to the alpha variant.

Although this study may imply a lower efficacy for the vaccine against the delta variant you need further real world studies and data to understand the impact on outcomes such as severe COVID-19 and deaths. It further highlights the importance of ensuring individuals receive both doses of the vaccine to get the best protection against variants of concern.

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Pfizer-BioNTech COVID-19 clinical trial finds effectiveness in children aged 12-15

This phase 3 clinical trial involved over 2200 children aged 12-15 who received two doses of the Pfizer-BioNTech COVID-19 vaccine 3 weeks apart. They compared the efficacy, safety and the immune response when compared to those aged 16-25.

Most of the side effects reported were mild to moderate and short lived (similar to those seen in older age cohorts). Furthermore laboratory tests confirmed that children aged 12-15 mounted a greater immune response when compared to young adults aged 16-25. 100% (95% CI, 75.3 to 100) efficacy is noted against symptomatic disease in children aged 12-15 after 7 days after the second dose.

Read more here:

A hypothesis exploring the pathogenesis of thromboembolism post vaccination with viral vector vaccines

This preprint paper from Germany outlines one hypothesis for the blood clots seen after vaccination with viral vector vaccines. They hypothesize that a delivery mechanism using adenoviral vectors to deliver the viral spike protein DNA to be transcribed in the nucleus is the issue as DNA derived from the RNA virus is not best transcribed in the nucleus and may result in production of variations of spike protein. These variants of the spike protein may induce the thromboembolic events . They tested their hypothesis using laboratory experiments.

Read more here:

UK Data on the Effectiveness of the Pfizer-BioNTech and AstraZeneca COVID-19 Vaccines Against the B.1.617.2 variant

This study looked at the effectiveness of COVID-19 vaccines against the B.1.617.2 variant (India).

The study was conducted using UK data and had 2 parts. First was a test negative case control study (comparing vaccination status in symptomatic cases to those who report symptoms but test negative). Second, they compared the proportion of cases with the B.1.617.2 variant relative to the main circulating virus (the B.1.1.7 variant, Kent) by vaccination status. 12,675 sequenced cases were included in the analysis of which 11,621 had B.1.1.7 detected and 1,054 had B.1.617.2 detected.

They found a reduction in effectiveness of one dose of vaccine against symptomatic disease with the B.1.617.2 variant.

Vaccine effectiveness against symptomatic disease with B.1.617.2 for a single dose of either vaccine was approximately 33%, for two doses of Pfizer vaccine effectiveness was approximately 88% and for two doses of AstraZeneca is approximately 60%.

This study estimates that there is reduced effectiveness of COVID-19 vaccines after one dose of Pfizer or AstraZeneca vaccine, however two doses of vaccine appeared to provide significant protection. Of note there was a limited follow up period in this study so they were unable to estimate effectiveness against severe illness, hospitalisation and death.

Read more here: 

Vaccine Effectiveness of mRNA COVID-19 Vaccines in Healthcare Workers (HCW) from the United States

This was a negative case control study, which estimates real world effectiveness of mRNA vaccines (Pfizer-BioNTech and Moderna® COVID-19 Vaccines) in HCWs in the USA. This paper reports results up to March 18 2021, at this point 623 case-patients and 1,220 controls had been enrolled. The majority of cases worked in direct patient contact roles and were aged between 19-49 years.

This study estimates a 2 dose effectiveness of mRNA vaccines of 94% (95% CI = 87%–97%) against symptomatic COVID-19. This was measured from 7 days after the second dose of vaccine. They also estimated a 1 dose effectiveness of 82% (95% confidence interval [CI] = 74%–87%), adjusted for age, race/ethnicity, and underlying medical conditions, this was measured from 14 days after first dose of vaccine.

This study among HCWs, which is ongoing, provides reassuring evidence that mRNA vaccines are highly effective in preventing symptomatic COVID-19 and correlate with trial data estimates.

Read more here:

TeenCOVE Study (Moderna) Releases Data on Effectiveness in Adolescents

Moderna have released Phase 2/3 study results for use of their mRNA vaccine in adolescents. Their study involved 3,732 adolescent participants ages 12 to less than 18 years. They were randomised to receive either 2 doses of mRNA vaccine or placebo. After two doses, no cases of COVID-19 were observed in the vaccine group using the case definition from the adult Phase 3 COVE study, compared to 4 cases in the placebo group, resulting in a vaccine efficacy of 100% starting 14 days after the second dose. Because symptoms in adolescents have been reported to be milder they also looked at those with mild symptoms, and created a case definition for testing of those people with milder symptoms for the adolescent trial. Using this case definition a vaccine efficacy of 93% was observed.

The vaccine was generally well tolerated in the population, and adverse events reported were similar to those in the adult trials. No significant safety concerns were identified. The majority of adverse events were mild or moderate in severity. The most common solicited local adverse event was injection site pain. The most common solicited systemic adverse events after the second dose of vaccine were headache, fatigue, myalgia and chills.

This study provides evidence that the Moderna COVID-19 vaccine is safe and effective in people ages 12 to 18, whereas the initial clinical trials only included those over 18 years of age. The company will now submit this data to the relevant authorities in various jurisdictions and seek approval for use of the vaccine in those aged 12 and over.

Read more here:

UK COVID-19 vaccine Booster Study Launched

The UK health secretary announced a large study which is to begin recruiting. The Cov-Boost study aims to identify find out which COVID-19 vaccines are most effective as a booster vaccination, depending on which vaccine was used to provide the initial prime-boost course. They are currently enrolling men and women over the age of 30 who received their initial prime-boost course of vaccination against COVID-19 in December 2020 or January 2021.

The study will evaluate the effect of a third/booster dose of one of seven different COVID-19 vaccines compared to a control group, who will receive a MenACWY vaccine. People are eligible to participate in the study if they have already received a COVID-19 vaccine.

The COVID-19 vaccines used in the study will be ChadOx1 nCoV-19 (Oxford/AstraZeneca), BNT162b2 (Pfizer BioNTech), mRNA-1273 (Moderna), NVX-CoV2373 (Novavax), VLA2001 (Valneva), CVnCoV (Curevac) and Ad26.COV2.S (Janssen).

Results are expected in 2022. Read more here: 

Moderna Booster Study Initial Data

In early May Moderna also announced initial phase 2 clinical trial data from a booster dose. The initial data indicates that a booster dose given to people who have previously been vaccinated increases antibody response against variants of concern (VOC)- B.1.351 (South Africa) and P.1 (Brazil). 3 booster vaccines are going to be studied: the original licensed vaccine from Moderna, a vaccine strain-matched to the VOC B.1.351 and a multivalent vaccine (combining the two aforementioned vaccines). Initial data shows the strain matched booster produced a higher antibody response against the VOC B.1.351 when compared with the original licensed vaccine as a booster. 

Read more here: 

Combining Influenza and COVID-19 Vaccination (ComFluCOV) study

The ComFluCOV trial is a study currently under way in the United Kingdom. It aims to examine the safety, as well as the immune responses, of administering the currently approved COVID-19 vaccines at the same time as the recommended influenza vaccines. It will include healthy adult volunteers, who will receive either influenza vaccine (Flucelvax QIV if the participant is less than 65 years old, or FluAd if the participant is aged 65 years or older) or control (saline), at the same time as receiving their second dose of COVID-19 vaccine (either Vaxzevria® or Comirnaty®).

Results are expected later this year.

Read more here: 

Public health impact of delaying second dose of BNT162b2 or mRNA-1273 COVID-19 vaccine: simulation agent based modeling study

This was a modelling study which compared the impact of the delayed second dose versus standard dosing vaccination strategies on SARS-CoV-2 infections and COVID-19 related hospital admissions and deaths. The authors included models with different vaccine efficacies, as well as different infection dynamics in the population. The study suggests a reduction in mortality, hospital admissions and deaths with a delayed vaccine strategy, particularly when delayed in the population under 65 years. The study however noted that this was found under conditions of vaccination rates being below 1% per day, and when vaccine rates were higher than 1% per day there was no difference in mortality and hospital admissions for delayed vaccine strategy. This modelling study provides evidence of benefit of a delayed second dose of mRNA vaccine strategy in the context of low vaccination rates or low supply of vaccine.

Romero-Brufau S, et al. 

BMJ 2021; 373

Extended interval BNT162b2 vaccination enhances peak antibody generation in older people

This was a cohort study in the UK, including 172 participants aged 80 and older. 99 participants received two doses 3 weeks apart (standard interval). 73 participants received the two doses 11-12 weeks apart (extended interval). 15 participants were excluded as serology indicated they had previous SARS-CoV-2 infection. Antibody responses were compared in both groups. Spike-specific antibodies were detected in 100% of participants in both groups 2-3 weeks after the second dose.The magnitude of the antibody response was compared in the two groups. Antibody titres in the standard-interval regimen peaked at 1138 U/ml after the second dose and then fell by 2.6-fold over the subsequent weeks (p<0.0001). Within the extended-interval cohort the median antibody titre was 17 U/ml at 5-6 weeks weeks after the first vaccine but showed a substantial 242-fold increase to reach 4030 after the second boost (p<0.0001). A comparison of the median magnitude of peak cellular responses after the second vaccine in the two schedules showed that these were higher for donors in the standard-interval regime (72 vs 20 spots/million; p<0.0001).

Parry H, et al.

Heterologous prime-boost COVID-19 vaccination: initial reactogenicity data

 This correspondence printed in the Lancet from the Com-COV study, a UK multicentre, participant-masked, randomised heterologous prime-boost COVID-19 vaccination study comparing different regimes of vaccination with AstraZeneca and Pfizer vaccination (receiving either both doses of same vaccine (homologous), or prime dose of one vaccine with second dose of different vaccine (heterologous). They found that those who received heterologous regime (different vaccine for second dose) reported more systematic reactions following second dose compared to those who received the same vaccine for their boost dose. Increased rates of fever, chills, fatigue, headache, joint pain, malaise, and muscle ache were reported in this group, compared to those reported after the second dose in homologous regime, along with increased use of paracetamol. The reactogenicity tended to resolve within 48 hours and was not associated with any adverse safety outcomes.

Shaw R. et al. 

Published: May 12, 2021

Effectiveness of BNT162b2 mRNA vaccine and ChAdOx1 adenovirus vector vaccine on mortality following COVID-19

This study looked at real world mortality data in England, estimating risk of mortality by vaccination status. Survival analysis showed an additional 44% protection against death after the first dose of Pfizer vaccine, 55% after the first dose of AstraZeneca vaccine, and 69% after the second dose of Pfizer vaccine. A single dose of either vaccine provided an efficacy of 80% against mortality and 97% for 2 doses of Pfizer vaccine. The study was not able to estimate efficacy of the second dose of AstraZeneca vaccine due to later rollout of that vaccine. This large observational study shows significant protection against mortality provided by these vaccines.

Lopez Bernal J, et al.

Effectiveness of BNT162b2 mRNA and ChAdOx1 adenovirus vector COVID-19 vaccines on risk of hospitalisation among older adults in England: an observational study using surveillance data

This study looked at the risk of hospitalisation, comparing those who are vaccinated and unvaccinated in England, using surveillance data for the first four months of the vaccination programme. In those aged 80 years and over, vaccine efficacy against hospitalisation was 73% following the first dose of AstraZeneca vaccine and 81% following the first dose of the Pfizer vaccine, and 93% following the second dose of the Pfizer vaccine. In those aged 70-79 years, vaccine effectiveness against hospitalisation was 84% following the first dose of Astrazeneca vaccine and 81% following the first dose of the Pfizer vaccine. This large observational study provides further real world effectiveness data for the Pfizer and Astrazeneca vaccines.

Ismail SA, et al

Real-world effectiveness of Ad26.COV2.S adenoviral vector vaccine for COVID-19

This study used surveillance data in the USA comparing those who had received one dose of Janssen vaccine to unvaccinated individuals, comparing outcomes. It estimates a vaccine effectiveness of 76.7% in preventing SARS-CoV-2 infection with onset at least two weeks after vaccination. Due to this vaccine being introduced relatively recently, data was not available to robustly study the effect of the Janssen vaccine on outcomes of mortality, hospitalisation and ICU admissions. This study provides real world data on the effectiveness of Janssen vaccine in preventing COVID-19 infection.

Corchado-Garcia J, et al.

Association Between Vaccination With BNT162b2 and Incidence of Symptomatic and Asymptomatic SARS-CoV-2 Infections Among Health Care Workers

This retrospective single site cohort study in Israel estimated the effect of Pfizer vaccine on SARS-CoV-2 infection in healthcare workers (symptomatic and asymptomatic). They estimated vaccine efficacy of 97% for preventing symptomatic infection and 86% for asymptomatic infection. This study provides further evidence that the vaccine is highly effective in preventing SARS-CoV-2 infection.

Angel Y, et al

Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons

This study highlights initial findings from safety reports following vaccination with mRNA COVID-19 vaccines during pregnancy in the United States between December 2020 and February 2021. The study reviewed data for pregnant women who received the mRNA based COVID-19 vaccines from Pfizer/ BioNTech or Moderna. Majority of the reported side effects were expected, mild to moderate and similar to non-pregnant individuals. Over 800 participants had a completed pregnancy; within this group maternal and foetal outcomes in the vaccinated cohort were similar to those seen in unvaccinated individuals pre-pandemic. Although the duration of follow-up was limited no safety signals were raised for these vaccines in pregnancy through the national adverse events monitoring database.

Shimabukuro TT, et al

N Engl J Med 2021;

Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data

This observational study reviews the impact of the national roll out of the Comirnaty® (PfizerBioNTech) COVID-19 mRNA Vaccine on outcomes in Israel.

By the start of April over 70% of the adult population (aged 16 and over) were fully vaccinated (21 days interval between doses). 7 days after completing the full vaccination schedule the following outcomes were found: 95% effectiveness against COVID-19 and 92% against asymptomatic COVID-19. It was around 97% effective against symptomatic COVID-19, COVID-19 related hospitalisation and deaths. The vaccine was effective against the B.1.1.7 (Kent) variant. This study provides further large-scale real-world effectiveness of this COVID-19 vaccine in line with the results from clinical trials.

Haas EJ et al

The Lancet Published May 05, 2021; DOI:

Effectiveness of the BNT162b2 Covid-19 Vaccine against the B.1.1.7 and B.1.351 Variants

Report from Qatar on the use of impact of a single dose of the Comirnaty® (PfizerBioNTech) COVID-19 mRNA Vaccine on COVID-19 variants: B.1.1.7 (Kent) and B.1.351 (South Africa).

These two variants were the main circulating strains in the country. A case-control observational review identified that two doses of the Pfizer-BioNTech COVID-19 vaccine (after 2 weeks) was nearly 90% effective against the B.1.1.7 variant and 75% effective against the B.1.351 variant. However, more importantly, it was around 97% effective against severe COVID-19 and COVID-19 related deaths in a population where both strains were pre-dominant. A cohort study design again found the vaccine to be 87% against the B.1.1.7 variant and 72% against the B.1.351 variant.

Abu-Raddad AJ et al

N Engl J Med 2021;

Prior SARS-CoV-2 infection rescues B and T cell responses to variants after first vaccine dose

The immune response (antibody, T and B cell) against COVID-19 variant (B.1.1.7 and B.1.351) in healthcare workers in the UK was measured followed one dose of the Comirnaty® (PfizerBioNTech) COVID-19 mRNA Vaccine (comparing those with or without previous COVID-19 infection).

The study found that pervious infection in conjunction with a single dose of the vaccine led to a better immune response (neutralising antibodies) against variants when compared to those who were infection naive and received a single dose of the vaccine. The study highlights the importance of completing the second dose of the vaccine schedule in those who are infection naïve.

Reynolds CJ et al

Science  30 Apr 2021;

Impact of vaccination on household transmission of SARS-COV-2 in England

This pre-print article from Public Health England examines the impact of vaccination (with Comirnaty® Pfizer/ BioNTech or Vaxzevria® COVID-19 Vaccine AstraZeneca) on transmission. They reviewed over 365,000 households with a case of COVID-19 and their 1 million contacts in England where the vaccine has been rolled out since December 2020.

Vaccinated people are less likely to develop symptomatic infection based on evidence from trials and other studies. However some people post vaccination may become infected with COVID-19. In such cases a single dose of either vaccine (21 days after vaccination), reduces the risk of transmission from cases to their household by 38-49% compared to unvaccinated individuals. This impact on transmission was evident from 2 weeks after vaccination. Furthermore, age of the case or contact was found to have limited impact on these findings. This real world study provides further evidence that vaccines may not just prevent infection but may also prevent transmission in cases of vaccine breakthrough.

Harris RJ et al

Public Health England, April 2021;

Effectiveness of Pfizer-BioNTech and Moderna Vaccines Against COVID-19 Among Hospitalized Adults Aged ≥65 Years — United States, January–March 2021

This case control study examines the effectiveness of the mRNA based COVID-19 vaccines (Comirnaty® from Pfizer/ BioNTech and COVID-19 vaccine Moderna®) against hospitalisation in older adults (aged 65 years and older) across various hospital sites in the United States between January and March 2021. The sample size was 417 patients. They estimate that the vaccines are 94% effective at reducing hospitalisation with COVID-19 after being fully vaccinated (2 weeks after second dose) and 64% effective following partial vaccination (2 weeks after first dose). Effectiveness in a real-world setting was therefore very similar to that seen in the trials of the vaccines.

Tenforde MW et al

MMWR Morb Mortal Wkly Rep 2021; DOI

The impact of SARS-CoV-2 vaccines on antibody responses in the general population in the United Kingdom

This study examined the impact of vaccination on antibody response in over 45,000 adults. Post vaccination with a single dose the antibody levels rose over time for all ages but in older adults (aged over 60 years) they increased at a slower rate and remained lower overall. However after two doses the antibody levels were high across all ages. There is some evidence of waning antibody levels after some time following the first dose of Comirnaty® (this is not seen after one dose of Vaxzevria®). Those who have previously had COVID-19 infection had high level of antibodies 28 days after a single dose of vaccine; similarly to those who are fully vaccinated without prior infection.

Wei J et al

medRxiv 2021; DOI:

Impact of vaccination on SARS-CoV-2 cases in the community: a population-based study using the UK’s COVID-19 Infection Survey

This study examined the impact of vaccination on laboratory confirmed COVID-19 infection rates. Data included swab results from over 370,000 people between December 2020 and April 2021 A 65% reduction in infections was noted following a single dose of both vaccines and 70% reduction following two doses of Comirnaty® (second doses of Vaxzevria® were not widely rolled out yet). Furthermore, infections in those who had been vaccinated had a lower viral load; therefore less likely to transmit the virus. The vaccines appear to be effective against the B.1.1.7 variant that is dominant in the UK and in Ireland.

Pritchard E et al

medRxiv 2021; DOI:

BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Mass Vaccination Setting

The study uses data from Israel’s largest health organisation to assess the real world effectiveness of Comirnaty® (Pfizer/BioNTech vaccine). The vaccine was given as two doses 21 days apart. A matched cohort study was undertaken involving nearly 1.2 million people (half of whom were vaccinated). Outcomes were measured after the first dose (day 14-20) and second dose (on or after day 7). This study provides real-world evidence of effectiveness of Comirnaty® vaccine against a number of clinical outcomes as summarised in Table 1. Subgroup analysis showed similar effectiveness across the ages. However, there may be marginally lower effectiveness in those with underlying health conditions. During the study period the incidence of COVID-19 was high and the dominant strain was the highly transmissible B.1.1.7 variant which is the dominant strain in Ireland.

Dagan N et al

N Engl J Med 2021;

COVID-19 dynamics after a national immunization program in Israel

This study reviews the impact of the vaccine at a population level in Israel over time. They retrospectively reviewed COVID-19 data for 6 months from end of August 2020. The vaccination programme started at the end of December 2020 using Comirnaty® vaccine (Pfizer/BioNTech) prioritising those at high risk. By the end of the study period nearly half of the population had received at least 1 dose of the vaccine. Over a third had received their second dose. Older adults are particular at higher risk and were initially prioritised; nearly 9 in 10 people aged over 60 years have received at least 1 dose at the end of the study period. Two months after the start of the vaccination programme which began with older adults, there was a concomitant drop in this age group in COVID-19 case rates, positivity rates, hospitalisation and severe cases. These trends were noticeable from 3-4 weeks after the vaccination programme started. This is largely attributed to the vaccination programme although other public health measures would have had an impact. This study demonstrates the real-world vaccine impact at a population level.

Rossman H et al

Nat Med 2021; DOI:

North West London Covid-19 Vaccination Programme: Real-world evidence for Vaccine uptake and effectiveness

This study, available as a preprint and not yet peer reviewed, is a study of 2,183,939 individuals eligible for COVID 19 vaccination in North-West London. The study linked primary and secondary care data to examine the risk of testing positive for COVID 19 in vaccinated and unvaccinated individuals.

Results showed that 28 days after vaccination there was a 74% (HR 0.26 (0.19-0.35)) and 78% (HR 0.22 (0.18-0.27)) reduction in the risk of testing positive for COVID-19 for individuals that received the Vaxzevria® COVID-19 Vaccine AstraZeneca and Comirnaty® Pfizer/ BioNTech COVID-19 mRNA vaccine respectively, when compared with unvaccinated individuals.

 After vaccination very low rates of hospital admission were seen in individuals testing positive for COVID-19 (0.01% of all patients vaccinated).

This study provides further evidence that a single dose of either Comirnaty® or Vaxzevria® is effective at reducing the risk of testing positive for COVID-19 up to 60 days after vaccination across all adult age groups, ethnic groups, and risk categories in an urban UK population.

There was no difference in effectiveness up to 28 days between Vaxzevria® and Comirnaty®.

Glampson B et al

medRxiv 2021; DOI:

Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers — Eight U.S. Locations, December 2020–March 2021

This study looked at the effectiveness of Comirnaty® Pfizer/BioNTech and COVID-19 vaccine Moderna® in preventing SARS-CoV-2 infections among 3,950 healthcare workers and other essential workers over a 13-week period from December 14, 2020 to March 13, 2021.

Participants self-collected nasal swabs each week regardless of whether they had developed symptoms of illness. Researchers were able to look for evidence of SARS-CoV-2 infection irrespective of symptoms. A small number (11%) of infections in this study were asymptomatic. The majority of infections (58%) occurred among people whose infections were identified by testing before they developed symptoms or knew they were infected.

Following a single dose of either vaccine, the participants’ risk of infection with SARS-CoV-2 was reduced by 80% two or more weeks after vaccination with a single dose. Results showed that following the second dose of vaccine, the risk of infection was reduced by 90% two or more weeks after vaccination.

The study demonstrates that these two mRNA vaccines can reduce the risk of all SARS-CoV-2 infections, not just symptomatic infections.

Thompson MG

MMWR Morb Mortal Wkly Rep 2021; DOI:

Vaccine effectiveness of the first dose of ChAdOx1 nCoV-19 and BNT162b2 against SARS-CoV-2 infection in residents of Long-Term Care Facilities (VIVALDI study)

This study examined the effectiveness of a first dose of Comirnaty® Pfizer/ BioNTech COVID-19 mRNA vaccine and Vaxzevria® (COVID-19 Vaccine AstraZeneca) against infection with SARS Co-V2 in residents of long-term care facilities.

 They compared more than 10,000 vaccinated and unvaccinated residents, undergoing routine asymptomatic testing (8 December 2020 - 15 March 2021). The estimated vaccine effectiveness against asymptomatic infection was estimated as 56% at 28-34 days, and 62% at 35-48 days following a single dose of  Vaxzevria® (COVID-19 Vaccine AstraZeneca) or Comirnaty® Pfizer/ BioNTech  COVID-19 mRNA vaccine. 

The findings suggest that the risk of SARS-CoV-2 infection is substantially reduced from 4 weeks following the first dose of either vaccine and that this effect is maintained for at least 7 weeks, with similar protection offered by both vaccine types. The analysis period coincided with the rapid emergence of B.1.1.7 in England during the second wave of the pandemic.

Shrotri M et al

medRxiv 2021; DOI:

Delayed Large Local Reactions to mRNA-1273 Vaccine against SARS-CoV-2

Blumenthal et al reported on local reactions in 12 patients following administration of mRNA-1273 (COVID-19 vaccine Moderna®) vaccine.

  • Median onset of reactions occurred day 8 after the vaccine (range 4-11 days).
  • Five of the reactions were grade 3 plaques (≥10 cm in diameter)
  • Some patients had concurrent systemic adverse effects, and among these patients, 2 had additional skin findings.
  • Most patients received treatment for their symptoms (e.g., with ice and antihistamines). Some patients received glucocorticoids (topical, oral, or both), and 1 patient received antibiotic therapy for presumptive cellulitis.
  • The symptoms resolved a median of 6 days after onset (range, 2 to 11).

Given that neither local injection-site reactions nor delayed-type hypersensitivity reactions are contraindications to subsequent vaccination, all 12 patients were encouraged to receive the second dose and completed their mRNA-1273 vaccination course.

  • Half the patients did not have a recurrence of large local reactions
  • Three patients had recurrent reactions that were similar to those after the initial dose
  • Three patients had recurrent reactions that were of a lower grade than those after the initial dose.
  • The median onset of cutaneous symptoms after the second dose (day 2; range, 1 to 3) was earlier than that after the first dose

Given the up-scaling of COVID-19 vaccination programmes worldwide the presentation of delayed local reactions such as those described here will become more common. It is important that these presentations are always reported to the appropriate regulatory authorities (Health Product Regulatory Authority (HPRA) in Ireland).

Blumenthal et al

N Engl J Med 2021; DOI:

Public Health England vaccine effectiveness report

This Public Health England report includes data on vaccine effectiveness in preventing hospitalisations and severe disease in individuals aged 80+ who had received one dose of Comirnaty® or Vaxzevria®. One dose of either vaccine had vaccine effectiveness against hospitalisation of approximately 80%.

The study also reported on the effects from a single dose of Comirnaty® Pfizer/BioNTech on the risk of mortality in symptomatic cases of COVID-19 aged 80 and older who had been vaccinated. This risk of death was reduced by 54%. Combined with the reduced risk of becoming a case, this is consistent with a vaccine effectiveness against mortality of approximately 85%.

Public Health England

Effect of vaccination on transmission of COVID-19: an observational study in healthcare workers and their households

This research involved over 300,000 people and ran between 8 December 2020 and 3 March 2021.The study compared cases and hospitalisations due to Covid-19 in household members of both vaccinated and unvaccinated health care workers.

The rate of infection with COVID-19 for people that live with healthcare workers was found to be at least 30% lower when the worker has been vaccinated with a single dose. Where healthcare workers had received a second dose of the vaccine at least 14 days before, their household members had a rate of COVID-19 which was at least 54% lower than household members where healthcare workers had not been vaccinated.

Anoop SVS et al

medRxiv 2021; DOI:

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

This is a study examining the efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine (also known as the COVID-19 Vaccine Moderna®) was published in the New England Journal of Medicine on February 4th 2021.

Efficacy:  This means that the efficacy of the vaccine in preventing symptomatic COVID-19 disease was 94.1% (95% CI 89.3%-96.8%; P<0.001) and was consistent in both younger (18-<65 years; vaccine efficacy= 95.6%) and older patients (>65 years; vaccine efficacy= 86.4%). Thirty patients in the trial developed severe COVID-19 disease all of whom were in the placebo group. This means that the mRNA-1273 SARS-CoV-2 vaccine was 100% effective at preventing severe COVID-19 disease.

Safety: Adverse events were more commonly reported in those who received two doses of the vaccine rather than two doses of the placebo (88.6% vs. 18.8%). The most commonly reported adverse events were injection-site reactions (mainly grade 1 or 2) and lasted for a mean of 2.6 and 3.2 days respectively. Most commonly reported systemic adverse events included headache, myalgia (muscle pain), arthralgia (bone pain), chills and fatigue and were more frequently reported after the second vaccine dose.

Summary: Overall this study shows that the efficacy of the COVID-19 Vaccine Moderna® vaccine in preventing both symptomatic COVID-19 and severe COVID-19 disease is high while the presence of adverse reactions post vaccine were limited to local injection-site reactions and some expected systemic reactions. Further studies examining the long-term duration of immunity of the COVID-19 Vaccine Moderna® are required.

Baden LR et al

N Engl J Med 2021;

Single – dose administration and the influence of the timing of the booster dose on immunogenicity and efficacy of ChAdOx1 nCov-10(AZD1222) vaccine: a pooled analysis of four randomised trials

A single standard dose Vaxzevria® (COVID-19 Vaccine AstraZeneca) provided protection against primary symptomatic COVID-19 in the first 90 days with an efficacy of 76·0% (95% CI 59·3 to 85·9), there was no evidence of waning of protection in the first three months after vaccination.

Vaccine efficacy after two standard doses was 55·1% (95% CI 33·0–69·9) with an interval of less than 6 weeks and 81·3% (60·3–91·2) when more than 12 weeks apart. Higher efficacy  was reported when the interval between the primary and booster dose are given more than 12 weeks apart.

Efficacy of a single standard dose against any NAAT (nucleic acid amplification test )-positive infection was 63·9% (46·0 to 75·9) from 22 days to 90 days, suggesting the potential for a substantial reduction in transmission, although these results are exploratory and require further investigation.

Merryn V et al

The Lancet Published February 19, 2021; DOI:

Safety and Immunogenicity of Two RNA-Based COVID-19 Vaccine Candidates

This study examined the safety and immunogenicity of two RNA-Based Covid-19 Vaccine candidates. The results of the study, added to earlier interim safety and immunogenicity data regarding BNT162b1 in younger adults from trials in Germany and the United States, supported the selection of *BNT162b2 for advancement to a pivotal phase 2–3 safety and efficacy evaluation .

*BNT162b2 is Comirnaty® (Pfizer/BioNTech)

Walsh E et al. 

N Engl J Med 2020;

Safety and Efficacy of the BNT162b2 mRNA COVID-19 Vaccine

A total of 43,548 people aged 16 years of age or older took part in this trial.43,448 people received injections: 21,720 with BNT162b2* vaccine and 21,728 with placebo. In the group that received BNT162b2 vaccine, there were 8 cases of Covid-19 with onset at least 7 days after the second dose. In the group that received placebo, there were 162 cases of COVID-19.

A two-dose regimen of BNT162b2 resulted in95% protection against COVID-19. Safety over a median of 2 months was similar to that of other viral vaccines. Adverse events were short-term. Most common were mild-to-moderate pain at the injection site, fatigue, and headache. The incidence of serious adverse events was low and was similar in the vaccine and placebo groups.

*BNT162b2  is Comirnaty® (Pfizer/BioNTech COVID-19 mRNA Vaccine)

Polack et al. 

New Engl J Med 2020;

Early effectiveness of COVID-19 vaccination with BNT162b2 mRNA vaccine and ChAdOx1 adenovirus vector vaccine on symptomatic disease, hospitalisations and mortality in older adults in England

A pre print study from Public Health England shows that both Comirnaty® (Pfizer/BioNTech COVID-19 mRNA Vaccine) and Vaxzevria® (COVID-19 Vaccine AstraZeneca) are highly effective in reducing COVID-19 infections among people aged 70 years and older.

Since January, protection against symptomatic COVID-19, 4 weeks after the first dose, ranged between 57% and 61% for 1 dose of Comirnaty® and between 60% and 73% for Vaxzevria® in this age group.

In people aged 80 years and older, data suggests that a single dose of either vaccine was more than 80% effective at preventing hospitalisation, 3 to 4 weeks after the vaccination.

Bernal JL et al

medRxiv 2021; DOI:

Assessing the Effectiveness of BNT162b2 and ChAdOx1nCoV-19 COVID-19 Vaccination in Prevention of Hospitalisations in Elderly and Frail Adults: A Single Centre Test Negative Case-Control Study

More real world data is available from the UK, the AvonCAP study showing substantial reductions in the risk of COVID-19-related hospitalisations after the Comirnaty® (Pfizer/BioNTech COVID-19 mRNA Vaccine) and Vaxzevria® (COVID-19 Vaccine AstraZeneca) vaccines among people aged ≥ 80 and older, including frail elderly people with extensive comorbid disease.

Vaccine effectiveness against COVID-19 related hospitalisation following one dose of Comirnaty® (Pfizer/BioNTech COVID-19 mRNA Vaccine) in this population was 71.4% and 80.4% for Vaxzevria® (COVID-19 Vaccine AstraZeneca) when measured ≥14 days after the first dose.

Hyams C et al

The Lancet Published 3 Mar 2021; DOI:

Effectiveness of First Dose of COVID-19 Vaccines Against Hospital Admissions in Scotland: National Prospective Cohort Study of 5.4 Million People

This study looked at the real-world effects of Comirnaty® Pfizer/BioNTech COVID-19 Vaccine and Vaxzevria® (COVID-19 Vaccine AstraZeneca) by estimating the effectiveness of the first dose of these COVID-19 vaccines in preventing hospital admissions in Scotland.

Surveillance data on cases was linked to primary care data, testing results, hospitalisation and mortality records for 5.4 million people in Scotland to estimate the effectiveness of vaccines to prevent COVID-19 related hospitalisation following the first dose of vaccine.

The first dose of the Comirnaty® was associated with a vaccine effect of 85% for COVID-19 related hospitalisation at 28-34 days post-vaccination. Vaccine effect at the same time interval for the Vaxzevria® was 94%. Results of combined vaccine effect for prevention of COVID-19 related hospitalisation were similar in people aged ≥80 years (81%; 95% CI 65 to 90 at 28-34 days post-vaccination).

In summary, this study concluded that a single dose of the Comirnaty® and Vaxzevria® vaccines resulted in substantial reductions in the risk of COVID-19 related hospitalisation in Scotland.

Vasileiou E et al

The Lancet Published 19 Feb 2021: DOI

Early rate reductions of SARS-CoV-2 infection and COVID-19 in BNT162b2 vaccine recipients

Data from Israel reported in the Lancet in February 2021 shows substantial early reductions in SARS-CoV-2 infection and symptomatic COVID-19 rates in healthcare workers following first vaccine dose administration.

The adjusted rate reduction of SARS-CoV-2 infection in vaccinated compared with unvaccinated individuals was 75% 15–28 days after first dose, and 30% 1–14 days after first dose.

For symptomatic COVID-19, adjusted rate reduction in vaccinated compared with unvaccinated individuals was 85% 15–28 days after first dose and 47% 1-14 days after a first dose.

Amit S et al

Emerg Infect Dis. 2021; DOI:

This page was updated 13 September 2021