Influence of COVID-19 Vaccination Coverage on Case Fatality Risk

Background: It is well known that COVID-19 vaccines demonstrate higher efficacy against mortality than mild acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The estimation of the proportion of mortalities among morbidities is a measure of the case fatality risk (CFR). To date, few studies have estimated the real-world CFR in relation to COVID-19 vaccination coverage. This study aims to evaluate the change in CFR estimates among different countries following the introduction of COVID-19 vaccines, and to identify the threshold dose of vaccines that changed the CFR as early as April 3, 2021. Furthermore, this study sheds light on the influence of COVID-19 vaccinations on the attack rate (AR), death rate, and, ultimately, CFR.

Material and Methods: We collected publicly available data concerning all countries and territories that implemented COVID-19 vaccination at least for 100 days, with an end date of April 3, 2021. In total, we found 16 countries and territories. The CFR was measured as the number of deaths per 100 COVID-19 confirmed cases, while vaccine coverage was defined as the number of doses of vaccine per 100 people in the total population.

We performed descriptive data analyses, including the mean value, standard deviation, and graphical presentation, using bar charts. Performed inferential data analyses included the one-sample Kolmogorov–Smirnov (K-S) test and general linear model procedure (GLM).

Results: Our findings showed a significantly associated decrease in the mean CFR in countries with > 18 COVID-19 vaccine doses per 100 inhabitants. We found a decrease from 1.88 % to 1.45 % with a (p-value =0.03), indicating a decrease in the proportion of total deaths to total cases. There was a decrease in the 95% confidence interval from 0.742-3.006 to 0. 718-2.179. The decrease in CFR was greater among the total deaths than total cases.

Conclusion: COVID-19 vaccination was found to decrease the COVID-19- CFR.

Recommendations: Post-interventional CFR monitoring may constitute a parameter for measuring vaccination effectiveness and progress of the current pandemic or future pandemics. Furthermore, post-interventional CFR estimates can be used as a parameter for assessment effectiveness of interventions e.g. COVID-19 vaccination effectiveness.