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Effectiveness of a Third Dose of BNT162b2 mRNA COVID-19 Vaccine in a Large US Health System: A Retrospective Cohort Study
35 Pages Posted: 21 Dec 2021More...
Background: Globally, recommendations are expanding for third (booster) doses of BNT162b2. In the United States, as of November 19, 2021, boosters were recommended for all adults aged 18 years and older. We evaluated the effectiveness of a third dose of BNT162b2 among adults in a large US integrated health system.
Methods: In this retrospective cohort study, we analyzed electronic health records from Kaiser Permanente Southern California between Dec 14, 2020 and Dec 5, 2021 to assess vaccine effectiveness (VE) of two and three doses of BNT162b2 against SARS-CoV-2 infections and COVID-19-related hospital admission. VE was calculated using hazards ratios from adjusted Cox models.
Findings: After only two doses, VE against infection declined from 85% (95% CI 83–86) during the first month to 49% (46–51) seven to eight months following vaccination. Overall VE against hospitalization was 90% (95% CI 86–92) within one month and did not wane, however, effectiveness against hospitalization appeared to wane among immunocompromised individuals. Three-dose VE was 88% (95% CI 86–89) against infection and 97% (95–98) against hospitalization. Effectiveness after three doses was higher than that seen one month after receiving only two doses for both outcomes. Relative VE of three doses compared to two (with at least six months after the second dose) was 75% (95% CI 71−78) and 70% (48−83) against infections and hospital admissions, respectively.
Interpretation: These data support the benefit of broad BNT162b2 booster recommendations, as three doses confers comparable, if not better, protection against SARS-CoV-2 infections and hospital admission as was seen soon after receiving two doses.
Trial Registration: This study was registered with: NCT04848584.
Funding: Pfizer Inc.
Declaration of Interest: JMZ, SG, SRV, KP, LJ, LP, and JMM are employees of and hold stock and/or stock options in Pfizer Inc. TBF holds stock in Pfizer Inc. SYT, JMS, VH, BA, HT, TF, SRS, and OO received research support from Pfizer during the conduct of this study that was paid directly to KPSC. All other authors report no conflicts.
Ethical Approval: The study protocol was reviewed and approved by the KPSC institutional review board which waived requirement for informed consent (number 12816).
Keywords: effectiveness, waning, booster, third dose, BNT162b2, SARS-CoV-2, COVID-19, United States, cohort, delta
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