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Effectiveness of mRNA BNT162b2 COVID-19 vaccine up to 6 months in a large integrated health system in the USA: a retrospective cohort study
Open accessAbstract
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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“Several studies have described a drop over time of two-dose vaccine effectiveness against SARS-CoV-2 symptomatic infection;”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [8]
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“this decrease in protection was substantially higher against Omicron BA.1 compared to Delta [3,8,12,19,26].”
From Vaccine effectiveness and duration of protection of COVID-19 mRNA vaccines against Delta and Omicron BA.1 symptomatic and severe COVID-19 outcomes in adults aged 50 years and over in France (2023) · cites this paper as [8]
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“Real-world setting studies performed, few months into vaccination campaigns, showed high effectiveness of these vaccines [1-8].”
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“However, as vaccination campaigns progressed, additional vaccine effectiveness (VE) studies revealed waning of the vaccine-induced protection over time [8-13]”
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“Yet, vaccine-induced immunity remains effective at preventing severe disease, hospitalization, and death, even at later time points when antibody levels may have declined (10–12).”
From mRNA vaccines induce durable immune memory to SARS-CoV-2 and variants of concern (2021) · cites this paper as [10]
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Research works printed but not linked: 1
- Lopez Bernal, 2021, Effectiveness of Covid-19 vaccines against the B.1.617.2 (delta) variant, N Engl J Med, 385, 585, 10.1056/NEJMoa2108891 · DOI · Paper page
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Metadata
- 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
- ORCID
- Venue
- The Lancet
- Publisher
- Elsevier BV
- Published
- 2021-10
- Volume
- 398
- Issue
- 10309
- Pages
- 1407-1416
- ISSN
- 0099-5355 (ISSN-L)
- 0140-6736
- PMC
- PMC8489881
- 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
- bronze
- doi.org
- Licence
- 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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