COVID-19 vaccinations are associated with reduced fatality rates: Evidence from cross-county quasi-experiments

Background Scientists have demonstrated the efficacy of vaccines against severe acute respiratory syndrome coronavirus 2 in randomized controlled trials. However, the extent to which reductions in COVID-19 case fatality ratio (CFR) are attributable to mass vaccination in the real world remains unclear. This study evaluated the association of COVID-19 vaccine coverage with CFR on a global scale. Methods The sample was a longitudinal data set of 90 countries over 25 weeks, from the first week of November 2020 to the third week of April 2021. CFR was measured in deaths per 100 COVID-19 confirmed cases; vaccine coverage was defined as the number of people who received at least one vaccine dose per 10 people in the total population. Data were retrieved from open-access databases, including Our World in Data and the Oxford COVID-19 Government Response Tracker. A country-level random effects model was used; a comprehensive set of variables for country characteristics and nonpharmaceutical interventions were included. Results A 10% increase in vaccine coverage was associated with a 7.6% reduction in the CFR (95% confidence interval (CI = -12.6 to -2.7%, P = 0.002). This association was stronger in countries with more effective governments (-8.3%; 95% CI = -13.6 to -3.1%, P = 0.002) and higher transport infrastructure quality (-8.1%; 95% CI = -13.3 to -2.9%, P = 0.002). Moreover, the vaccine coverage was associated with a reduced CFR in a dose-dependent manner. When vaccine coverage achieved 0.8 to 1.6, 1.6 to 3.2 and =3.2 per 10 people, the CFR reduced by 12.7% (95 CI = -21.8 to -3.6%, P = 0.006), 21.2% (95 CI = -33.9 to -8.5%, P = 0.001) and 31.3% (95 CI = -51.5 to -11.0%, P = 0.002), respectively as compared with no vaccination. Conclusions Our results provide supporting evidence that vaccination is critical to preventing deaths among infected people. Vaccination programmes have yielded significant health benefits in certain countries. However, globally, a large gap remains between observed and achievable fatality reductions. Continuous improvement in vaccine coverage will be critical to transforming efficacious vaccines into desired health outcomes.