Background: Methodologically rigorous studies on Covid-19 vaccine effectiveness (VE) in preventing SARS-CoV-2 infection are critically needed to inform national and global policy on Covid-19 vaccine use. In Israel, healthcare personnel (HCP) were initially prioritized for Covid-19 vaccination, creating an ideal setting to evaluate early real-world VE in a closely monitored population. Methods: We conducted a prospective study among HCP in 6 hospitals to estimate the effectiveness of the BNT162b2 mRNA Covid-19 vaccine in preventing SARS-CoV-2 infection. Participants filled out weekly symptom questionnaires, provided weekly nasal specimens, and three serology samples – at enrollment, 30 days and 90 days. We estimated VE against PCR-confirmed SARS-CoV-2 infection using the Cox Proportional Hazards model and against a combined PCR/serology endpoint using Fisher's exact test. Results: Of the 1567 HCP enrolled between December 27, 2020 and February 15, 2021, 1250 previously uninfected participants were included in the primary analysis; 998 (79.8%) were vaccinated with their first dose prior to or at enrollment, all with Pfizer BNT162b2 mRNA vaccine. There were four PCR-positive events among vaccinated participants, and nine among unvaccinated participants. Adjusted two-dose VE against any PCR-confirmed infection was 94.5% (95% CI: 82.6%-98.2%); adjusted two-dose VE against a combined endpoint of PCR and seroconversion for a 60-day follow-up period was 94.5% (95% CI: 63.0%-99.0%). Five PCR-positive samples from study participants were sequenced; all were alpha variant. Conclusions: Our prospective VE study of HCP in Israel with rigorous weekly surveillance found very high VE for two doses of Pfizer BNT162b2 mRNA vaccine against SARS-CoV-2 infection in recently vaccinated HCP during a period of predominant alpha variant circulation. Funding: Clalit Health Services.
Bibliographical noteFunding Information:
We thank Nadav Raviv and Ilan Gofer from Clalit Research Institute, Innovation Division for helping with the data collection throughout the study, Sydney Krispin from Clalit Research Institute, Innovation Division for helping with the manuscript submission. We also thank Arnold Monto, Emily Martin, Josh Petrie and Ryan Malosh from University of Michigan School of Public Health for providing input on the analysis plan. We thank Yossef Rosemberg from Clalit Central laboratory for his help with the serology testing. We thank Svetlana Rothe, Ranin Wahab, Tamar Amar and Tal Eylon from Rabin Medical Center, Anna Yanovskay, Carmel Kasher, Merav Strauss and Hana Kahanov Edelstein from Ha'Emek Medical Center, Ayman Fadeela and Galit Carmon from Meir Medical Center, Iris Greenbaum, Nataliya Kyrylyshyn, Yosfit Yosefa Mussa, Abeer Bdeer, Inbar Gesua Abu from Schneider Children's Medical Center of Israel, Ayelet Sherman, Shlomit shick, Lihi Geler and Hana Leiba from Kaplan Medical Center, Orli Zamir- Barashi and the pediatric infectious disease unit from Soroka University Medical Center for recruiting participants, collecting samples and following-up on participant questionnaires during the study. We thank the Israeli Ministry of Health for providing serology kits for the 30-day and 90-day serology tests. We also thank all the participants for their contribution throughout the study.
© 2021 Elsevier Ltd
ASJC Scopus subject areas
- Molecular Medicine
- Immunology and Microbiology (all)
- Veterinary (all)
- Public Health, Environmental and Occupational Health
- Infectious Diseases