Effectiveness of an Inactivated SARS-CoV-2 Vaccine in Chile

TLDR

Mass vaccination campaigns to prevent COVID‑19 are occurring worldwide, and estimates of vaccine effectiveness are urgently needed to guide decisions. The study aimed to evaluate the effectiveness of Chile’s nationwide CoronaVac vaccination campaign in preventing COVID‑19 and severe outcomes. A prospective national cohort of 10.2 million adults was analyzed with an extended Cox proportional‑hazards model that incorporated time‑varying vaccination status and adjusted for demographic and clinical factors. Full immunization with CoronaVac yielded 65.9 % effectiveness against COVID‑19, 87.5 % against hospitalization, 90.3 % against ICU admission, and 86.3 % against COVID‑19‑related death. Funding was provided by Chile’s Agencia Nacional de Investigación y Desarrollo and other agencies.

Abstract

BackgroundMass vaccination campaigns to prevent coronavirus disease 2019 (Covid-19) are occurring in many countries; estimates of vaccine effectiveness are urgently needed to support decision making. A countrywide mass vaccination campaign with the use of an inactivated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine (CoronaVac) was conducted in Chile starting on February 2, 2021.MethodsWe used a prospective national cohort, including participants 16 years of age or older who were affiliated with the public national health care system, to assess the effectiveness of the inactivated SARS-CoV-2 vaccine with regard to preventing Covid-19 and related hospitalization, admission to the intensive care unit (ICU), and death. We estimated hazard ratios using the extension of the Cox proportional-hazards model, accounting for time-varying vaccination status. We estimated the change in the hazard ratio associated with partial immunization (≥14 days after receipt of the first dose and before receipt of the second dose) and full immunization (≥14 days after receipt of the second dose). Vaccine effectiveness was estimated with adjustment for individual demographic and clinical characteristics.ResultsThe study was conducted from February 2 through May 1, 2021, and the cohort included approximately 10.2 million persons. Among persons who were fully immunized, the adjusted vaccine effectiveness was 65.9% (95% confidence interval [CI], 65.2 to 66.6) for the prevention of Covid-19 and 87.5% (95% CI, 86.7 to 88.2) for the prevention of hospitalization, 90.3% (95% CI, 89.1 to 91.4) for the prevention of ICU admission, and 86.3% (95% CI, 84.5 to 87.9) for the prevention of Covid-19–related death.ConclusionsOur results suggest that the inactivated SARS-CoV-2 vaccine effectively prevented Covid-19, including severe disease and death, a finding that is consistent with results of phase 2 trials of the vaccine. (Funded by Agencia Nacional de Investigación y Desarrollo and others.) Visual Abstract Effectiveness of an Inactivated SARS-CoV-2 Vaccine