Cited by 1,167SARS-CoV-2 and COVID-19 ResearchVaccine Coverage and HesitancyCOVID-19 epidemiological studies

Effectiveness of mRNA BNT162b2 COVID-19 vaccine up to 6 months in a large integrated health system in the USA: a retrospective cohort study

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Tartof, Sara Y, Slezak, Jeff M, Fischer, Heidi, Hong, Vennis, Ackerson, Bradley K, Ranasinghe, Omesh N, Frankland, Timothy B, Ogun, Oluwaseye A +7 more·2021·The Lancet

Abstract

Background Vaccine effectiveness studies have not differentiated the effect of the delta (B.1.617.2) variant and potential waning immunity in observed reductions in effectiveness against SARS-CoV-2 infections. We aimed to evaluate overall and variant-specific effectiveness of BNT162b2 (tozinameran, Pfizer-BioNTech) against SARS-CoV-2 infections and COVID-19-related hospital admissions by time since vaccination among members of a large US health-care system. Methods In this retrospective cohort study, we analysed electronic health records of individuals (≥12 years) who were members of the health-care organisation Kaiser Permanente Southern California (CA, USA), to assess BNT162b2 vaccine effectiveness against SARS-CoV-2 infections and COVID-19-related hospital admissions for up to 6 months. Participants were required to have 1 year or more previous membership of the organisation. Outcomes comprised SARS-CoV-2 PCR-positive tests and COVID-19-related hospital admissions. Effectiveness calculations were based on hazard ratios from adjusted Cox models. This study was registered with ClinicalTrials.gov, NCT04848584. Findings Between Dec 14, 2020, and Aug 8, 2021, of 4 920 549 individuals assessed for eligibility, we included 3 436 957 (median age 45 years [IQR 29-61]; 1 799 395 [52·4%] female and 1 637 394 [47·6%] male). For fully vaccinated individuals, effectiveness against SARS-CoV-2 infections was 73% (95% CI 72-74) and against COVID-19-related hospital admissions was 90% (89-92). Effectiveness against infections declined from 88% (95% CI 86-89) during the first month after full vaccination to 47% (43-51) after 5 months. Among sequenced infections, vaccine effectiveness against infections of the delta variant was high during the first month after full vaccination (93% [95% CI 85-97]) but declined to 53% [39-65] after 4 months. Effectiveness against other (non-delta) variants the first month after full vaccination was also high at 97% (95% CI 95-99), but waned to 67% (45-80) at 4-5 months. Vaccine effectiveness against hospital admissions for infections with the delta variant for all ages was high overall (93% [95% CI 84-96]) up to 6 months. Interpretation Our results provide support for high effectiveness of BNT162b2 against hospital admissions up until around 6 months after being fully vaccinated, even in the face of widespread dissemination of the delta variant. Reduction in vaccine effectiveness against SARS-CoV-2 infections over time is probably primarily due to waning immunity with time rather than the delta variant escaping vaccine protection. Funding Pfizer.

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  1. Lopez Bernal J, Andrews N, Gower C, et al. Effectiveness of Covid-19 vaccines against the B.1.617.2 (delta) variant. N Engl J Med 2021; 385: 585-94.

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Authors
Tartof, S. Y., Slezak, J. M., Fischer, H., Hong, V., Ackerson, B. K., Ranasinghe, O. N., Frankland, T. B., Ogun, O. A., Zamparo, J. M., Gray, S., Valluri, S. R., Pan, K., Angulo, F. J., Jodar, L., & McLaughlin, J. M.
Affiliations
  • Kaiser Permanente (US)
  • Pfizer (United States) (US)
Corresponding author
Tartof, Sara Y
Venue
The Lancet
Publisher
Elsevier BV
Published
2021-10
Volume
398
Issue
10309
Pages
1407-1416
ISSN
  • 0099-5355 (ISSN-L)
  • 0140-6736
OpenAlex
W3202826390
Cited by
1,167
References
37
Citations by year
2026: 33 · 2025: 70 · 2024: 116 · 2023: 257 · 2022: 583 · 2021: 108
FWCI
84.33
Type
journal article
Language
en
Open access
Locations
  • The Lancet (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
Pfizer Inc Boulder
Topics
  • Health Sciences › Medicine › Infectious Diseases › SARS-CoV-2 and COVID-19 Research
  • Social Sciences › Health › Vaccine Coverage and Hesitancy
  • Physical Sciences › Mathematics › Modeling and Simulation › COVID-19 epidemiological studies
Keywords
BNT162b2, COVID-19 vaccines, mRNA vaccines, vaccine effectiveness, COVID-19 pandemic, COVID-19 hospitalization, Delta variant, waning immunity, integrated health system, Kaiser Permanente, time since vaccination, SARS-CoV-2 sequencing
MeSH terms
COVID-19, SARS-CoV-2, COVID-19 Vaccines, BNT162 Vaccine, Adolescent, Adult, Aged, Aged, 80 and over, Child, Female, Hospitalization, Humans, Male, Middle Aged, Organizations, Retrospective Studies, RNA, Messenger, Time Factors, United States, Vaccination, Delivery of Health Care, Integrated

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