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

N Engl J Med. 2021 Sep 2;385(10):875-884. doi: 10.1056/NEJMoa2107715. Epub 2021 Jul 7.


Background: Mass 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.

Methods: We 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.

Results: The 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.

Conclusions: Our 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.).

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • COVID-19 / epidemiology
  • COVID-19 / mortality
  • COVID-19 / prevention & control*
  • COVID-19 Vaccines / immunology*
  • Chile / epidemiology
  • Female
  • Hospitalization / statistics & numerical data
  • Humans
  • Immunogenicity, Vaccine*
  • Incidence
  • Intensive Care Units
  • Male
  • Mass Vaccination*
  • Middle Aged
  • Patient Acuity
  • Prospective Studies
  • Treatment Outcome
  • Vaccines, Inactivated
  • Young Adult


  • COVID-19 Vaccines
  • Vaccines, Inactivated