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: https://doi.org/10.1016/S0140-6736(21)01420-3