Population-Level Effectiveness of an Inactivated Whole-Virion COVID-19 Vaccine: A Test Negative Case-Control Study in the Dominican Republic

Abstract

Background A continuing nationwide vaccination campaign began in the Dominican Republic on February 16, 2021 to prevent severe consequences of acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Estimates of vaccine effectiveness under real-world conditions are needed to support policy decision making and inform further vaccine selection. Methods We conducted a test-negative case-control study to assess the real-world effectiveness of nationwide coronavirus disease 2019 (COVID-19) vaccination program using an inactivated vaccine (CoronaVac®) on preventing symptomatic SARS-CoV-2 infections and hospitalizations from August to November 2021 in the Dominican Republic. Participants were recruited from 10 hospitals in 5 provinces to estimate the effectiveness of full immunization (≥14 days after receipt of the second dose) and partial immunization (otherwise with at least one dose ≥14 days after receipt of the first dose). Results Of 1,078 adult participants seeking health care for COVID-19-related symptoms, 395 (36.6%) had positive polymerase chain reaction (PCR) tests for SARS-CoV-2; 142 (13.2%) were hospitalized during 15 days of follow-up, including 91 (23%) among 395 PCR-positive and 51 (7.5%) among 683 PCR-negative participants. Full vaccination was associated with 31% lower odds of symptomatic infection (odds ratio, 0.69; 95% confidence interval, 0.52-0.93) and partial vaccination was associated with 49% lower odds (0.51; 0.30-0.86). Among 395 PCR-positive participants, full vaccination reduced the odds of COVID-19 related hospitalization by 85% (0.15; 0.08-0.25) and partial vaccination reduced it by 75% (0.25; 0.08-0.80); full vaccination was associated with reduced use of assisted ventilation by 73% (0.27; 0.15-0.49). Conclusions Given the ancestral and delta viral variants circulating during this study period, our results suggest that the inactivated COVID-19 vaccine offered moderate protection against symptomatic SARS-CoV-2 infections and high protection against COVID-19 related hospitalizations and assisted ventilation. This is reassuring given that, as of August 2022, an estimated 2.6 billion inactivated CoronaVac® vaccine doses had been administered worldwide. This vaccine will become a basis for developing multivalent vaccine against currently circulating omicron variant.