Pfizer/BioNTech reported that data in individuals who received a third dose of Comirnaty® show a favourable safety profile and robust immune responses. The additional dose elicited significantly higher neutralising antibody titres against the initial SARS-CoV-2 virus (wild type), and the Beta and Delta variants, compared to the levels observed after the two-dose primary series.
Two reports of successful enhancement of immune response in solid organ transplant recipients have been reported. In a randomised controlled trial with 120 organ transplant recipients, median age 66 years, an additional dose of Spikevax® (Moderna) was given two months after the second dose and resulted in significant increases in antibody levels and neutralising antibody activity.
There is also preliminary evidence of the safety of giving a 3rd mRNA vaccine dose from Israel where a population-based booster programme of Comirnaty® administered to approximately one million people has already taken place. Data shared by the Israeli Health Ministry reported that no safety concerns were identified with similar safety profiles but lower rates of systemic and local reactions were reported than following the first or second doses.