Vaccine Coverage Associated with Ending a Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Wave: A Retrospective Longitudinal Analysis

Background: Two SARS-CoV-2 waves in Israel ended while a substantial number of individuals remained unvaccinated or partially vaccinated. The indirect protective effect of the first BNT162b2 vaccination campaign in Israel was evaluated between 22 December 2020 and 18 May 2021. Methods: The daily percentage of new polymerase chain reaction (PCR)-confirmed SARS-CoV-2 cases among unvaccinated individuals was analyzed for trends. Major shifts were identified using piecewise linear regression analysis. At these shifts, the percentage of naturally vaccinated (past SARS-CoV-2 cases) and the percentage of actively vaccinated (by inoculation) individuals were weighted and summed to determine the percentage of natural and active vaccination (NAV). Results: A first decline among unvaccinated individuals occurred during a lockdown period, when the percentage of NAV was 8.16%. The major decline occurred after the end of the lockdown when the percentage of NAV reached 52.05%. SARS-CoV-2 cases ultimately declined among unvaccinated individuals when the percentage of NAV reached 63.55%. During the study period, the Alpha variant was prevalent and the use of nonpharmaceutical interventions, including social distancing, existed to varying degrees. Conclusions: The vaccination campaign played a major role in the decline of SARS-CoV-2 infection among unvaccinated individuals, leading to the end of the first 2021 SARS-CoV-2 wave (Alpha variant) in Israel. Infection in unvaccinated individuals stopped when two-Thirds of the population were naturally or actively vaccinated. Any change in characteristics of the virus or the population can lead to a new outbreak.