• Edson D Moreira, Nicholas Kitchin, Xia Xu, Samuel S Dychter, Stephen Lockhart, Alejandra Gurtman, John L Perez, Cristiano Zerbini, Michael E Dever, Timothy W Jennings, Donald M Brandon, Kevin D Cannon, Michael J Koren, Douglas S Denham, Mezgebe Berhe, David Fitz-Patrick, Laura L Hammitt, Nicola P Klein, Haylene Nell, Georgina Keep, Xingbin Wang, Kenneth Koury, Kena A Swanson, David Cooper, Claire Lu, Özlem Türeci, Eleni Lagkadinou, Dina B Tresnan, Philip R Dormitzer, Uğur Şahin, William C Gruber, Kathrin U Jansen, and C4591031 Clinical Trial Group.
• From Associação Obras Sociais Irmã Dulce and the Oswaldo Cruz Foundation, Bahia (E.D.M.), and Centro Paulista de Investigação Clinica, São Paulo (C.Z.) - both in Brazil; Vaccine Research and Development, Pfizer, Hurley, United Kingdom (N.K., S.L., G.K.); Vaccine Research and Development, Pfizer, Collegeville, PA (X.X., J.L.P., X.W.); Vaccine Research and Development, Pfizer (S.S.D.), and California Research Foundation (D.M.B.), San Diego, and Kaiser Permanente Vaccine Study Center, Oakland (N.P.K.) - all in California; Vaccine Research and Development, Pfizer, Pearl River, NY (A.G., K.K., K.A.S., D.C., C.L., P.R.D., W.C.G., K.U.J.); Clinical Neuroscience Solutions, Orlando (M.E.D.), and Jacksonville Center for Clinical Research, Jacksonville (M.J.K.) - both in Florida; Clinical Research Professionals, Chesterfield, MO (T.W.J.); Accellacare, Wilmington, NC (K.D.C.); Clinical Trials of Texas, San Antonio (D.S.D.), and North Texas Infectious Diseases Consultants, Dallas (M.B.); East-West Medical Research Institute, Honolulu (D.F.P.); Johns Hopkins Bloomberg School of Public Health, Baltimore (L.L.H.); Tiervlei Trial Centre, Karl Bremer Hospital, Cape Town, South Africa (H.N.); BioNTech, Mainz, Germany (Ö.T., E.L., U.Ş.); and Worldwide Safety, Safety Surveillance and Risk Management, Pfizer, Groton, CT (D.B.T.).
• N. Engl. J. Med. 2022 May 19; 386 (20): 191019211910-1921.

BackgroundActive immunization with the BNT162b2 vaccine (Pfizer-BioNTech) has been a critical mitigation tool against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during the coronavirus disease 2019 (Covid-19) pandemic. In light of reports of waning protection occurring 6 months after the primary two-dose vaccine series, data are needed on the safety and efficacy of offering a third (booster) dose in persons 16 years of age or older.MethodsIn this ongoing, placebo-controlled, randomized, phase 3 trial, we assigned participants who had received two 30-μg doses of the BNT162b2 vaccine at least 6 months earlier to be injected with a third dose of the BNT162b2 vaccine or with placebo. We assessed vaccine safety and efficacy against Covid-19 starting 7 days after the third dose.ResultsA total of 5081 participants received a third BNT162b2 dose and 5044 received placebo. The median interval between dose 2 and dose 3 was 10.8 months in the vaccine group and 10.7 months in the placebo group; the median follow-up was 2.5 months. Local and systemic reactogenicity events from the third dose were generally of low grade. No new safety signals were identified, and no cases of myocarditis or pericarditis were reported. Among the participants without evidence of previous SARS-CoV-2 infection who could be evaluated, Covid-19 with onset at least 7 days after dose 3 was observed in 6 participants in the vaccine group and in 123 participants in the placebo group, which corresponded to a relative vaccine efficacy of 95.3% (95% confidence interval, 89.5 to 98.3).ConclusionsA third dose of the BNT162b2 vaccine administered a median of 10.8 months after the second dose provided 95.3% efficacy against Covid-19 as compared with two doses of the BNT162b2 vaccine during a median follow-up of 2.5 months. (Funded by BioNTech and Pfizer; C4591031 ClinicalTrials.gov number, NCT04955626.).Copyright © 2022 Massachusetts Medical Society.

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