Effectiveness of BNT162b2 mRNA COVID-19 Vaccine Against Acquisitions of SARS-CoV-2 Among Health Care Workers in Long-Term Care Facilities: A Prospective Cohort Study

Abstract

Background: We assessed vaccine effectiveness (VE) of BNT162b2 mRNA COVID-19 vaccine against SARS-CoV-2 acquisition among health care workers (HCWs) of long-term care facilities (LTCFs). \n \nMethods: This prospective study, in the framework of Senior Shield program in Israel, included routine, weekly nasopharyngeal SARS-CoV-2 RT-PCR testing from all LTCF HCWs since July 2020. All residents and 75% of HCWs were immunized between December 2020 and January 2021. The analysis was limited to HCWs adhering to routine testing. Fully vaccinated (14+ days after second dose; n=6960) and unvaccinated HCWs (n=2202) were simultaneously followed until SARS-CoV-2 acquisition, or end of follow-up, April 11, 2021. Hazard ratios (HR) for vaccination vs. no vaccination were calculated (Cox proportional hazards regression models, adjusting for socio-demographics and residential-area COVID-19 incidence). VE was calculated as [(1– HR)×100]. RT-PCR cycle threshold values (Cts) were compared between vaccinated and unvaccinated HCWs. \n \nFindings: At >14 days post second dose, 40 vaccinated HCWs acquired SARS-CoV-2 (median follow-up, 66 days; cumulative incidence 0·6%) vs. 84 unvaccinated HCWs (median follow-up 43 days; cumulative incidence, 5·1%); HR=0·11 (95% CI 0·07, 0.17), unadjusted VE=89% (95% CI 83%, 93%). Adjusted VE beyond seven days and >14 days post second dose were similar. The median PCR Cts targeting ORF1ab gene among 20 vaccinated and 40 unvaccinated HCWs was 32·0 vs. 26·7, respectively, p=0·008. \n \nInterpretation: VE following two doses of BNT162b2 against SARS-CoV-2 acquisition in LTCF HCWs was high. The lower viral loads among SARS-CoV-2 positive HCWs suggests further reduction in transmission. \n \nFunding Information: The current study did not have external funding sources. \n \nDeclaration of Interests: None. \n \nEthics Approval Statement: The study protocol was approved by the institutional review board of the Soroka University Medical Center, Beer-Sheva, Israel.