Effectiveness of a Third Dose of Pfizer-BioNTech and Moderna Vaccines in Preventing COVID-19 Hospitalization Among Immunocompetent and Immunocompromised Adults - United States, August-December 2021.

COVID-19 mRNA vaccines (BNT162b2 [Pfizer-BioNTech] and mRNA-1273 [Moderna]) provide protection against infection with SARS-CoV-2, the virus that causes COVID-19, and are highly effective against COVID-19-associated hospitalization among eligible persons who receive 2 doses (1,2). However, vaccine effectiveness (VE) among persons with immunocompromising conditions* is lower than that among immunocompetent persons (2), and VE declines after several months among all persons (3). On August 12, 2021, the Food and Drug Administration (FDA) issued an emergency use authorization (EUA) for a third mRNA vaccine dose as part of a primary series ≥28 days after dose 2 for persons aged ≥12 years with immunocompromising conditions, and, on November 19, 2021, as a booster dose for all adults aged ≥18 years at least 6 months after dose 2, changed to ≥5 months after dose 2 on January 3, 2022 (4,5,6). Among 2,952 adults (including 1,385 COVID-19 case-patients and 1,567 COVID-19-negative controls) hospitalized at 21 U.S. hospitals during August 19-December 15, 2021, effectiveness of mRNA vaccines against COVID-19-associated hospitalization was compared between adults eligible for but who had not received a third vaccine dose (1,251) and vaccine-eligible adults who received a third dose ≥7 days before illness onset (312). Among 1,875 adults without immunocompromising conditions (including 1,065 [57%] unvaccinated, 679 [36%] 2-dose recipients, and 131 [7%] 3-dose [booster] recipients), VE against COVID-19 hospitalization was higher among those who received a booster dose (97%; 95% CI = 95%-99%) compared with that among 2-dose recipients (82%; 95% CI = 77%-86%) (p <0.001). Among 1,077 adults with immunocompromising conditions (including 324 [30%] unvaccinated, 572 [53%] 2-dose recipients, and 181 [17%] 3-dose recipients), VE was higher among those who received a third dose to complete a primary series (88%; 95% CI = 81%-93%) compared with 2-dose recipients (69%; 95% CI = 57%-78%) (p <0.001). Administration of a third COVID-19 mRNA vaccine dose as part of a primary series among immunocompromised adults, or as a booster dose among immunocompetent adults, provides improved protection against COVID-19-associated hospitalization.
Competing Interests: All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. Samuel M. Brown reports personal fees from Hamilton, institutional fees from Faron Pharmaceuticals and Sedana, grants from Janssen, the National Institutes of Health (NIH), the Department of Defense (DoD), book royalties from Oxford University and Brigham Young University, outside the submitted work. Steven Y. Chang was a speaker for La Jolla Pharmaceuticals in 2018 and consulted for PureTech Health in 2020. James D. Chappell reports grants from NIH during the conduct of the study. Abhijit Duggal reports grants from NIH and participation on a steering committee for ALung Technologies, Inc., outside the submitted work. Matthew C. Exline reports support from Abbott Labs for sponsored talks, outside the submitted work. D. Clark Files reports personal consultant fees from Cytovale and is a data and safety monitoring board (DSMB) member from Medpace, outside the submitted work. Manjusha Gaglani reports grants from CDC-Vanderbilt University Medical Center for the submitted work, CDC-Abt Associates, CDC-Westat, Janssen and Pfizer, outside the submitted work. Adit A. Ginde reports grants from NIH, DoD, AbbVie, and Faron Pharmaceuticals, outside the submitted work. Michelle N. Gong reports grants from NIH and the Agency for Healthcare Research and Quality (AHRQ), DSMB membership fees from Regeneron, outside the submitted work. Carlos G. Grijalva reports consultancy fees from Pfizer, Merck, and Sanofi-Pasteur; grants from Campbell Alliance/Syneos Health, NIH, the Food and Drug Administration, AHRQ, and Sanofi, outside the submitted work. David N. Hager reports salary support from Incyte Corporation and EMPACT Precision Medicine via Vanderbilt University Medical Center and grants from NHLBI, outside the submitted work. Natasha Halasa reports grants and nonfinancial support from Sanofi, and grants from Quidel outside the submitted work. Akram Khan reports grants from United Therapeutics, Johnson & Johnson, Ely Lilly, and GlaxoSmithKline, outside the submitted work. Adam S. Lauring reports personal fees from Sanofi and Roche, outside the submitted work. Christopher J. Lindsell reports grants from NIH, DoD, and the Marcus Foundation; contract fees from bioMerieux, Endpoint LLC, and Entegrion Inc, outside the submitted work; in addition, Dr. Lindsell has a patent for risk stratification in sepsis and septic shock issued. Emily T. Martin reports personal fees from Pfizer and grants from Merck, outside the submitted work. Ithan D. Peltan reports grants from NIH, Janssen Pharmaceuticals and institutional support from Asahi Kasei Pharma and Regeneron, outside the submitted work. Todd W. Rice reports personal fees from Cumberland Pharmaceuticals, Inc, Cytovale, Inc., and Sanofi, Inc., outside the submitted work. Wesley H. Self reports consulting fees from Aeprio Pharmaceuticals and Merck, outside the submitted work. No other potential conflicts of interest were disclosed.