Quantifying the real-life impacts of vaccination on critical COVID-19
The effectiveness of individual prophylaxis of symptomatic or severe COVID-19 by anti-SARS-CoV-2 vaccination is now well established. However, real-life quantification of the vaccine impact on critical COVID-19 forms -- which require critical care and may lead to death -- is still lacking, especially because simultaneous reduction in community spread has to be accounted for. In this study, we use an epidemiological model tailored to capture hospital dynamics in France to investigate counterfactual scenarios, including purely collective and purely individual vaccines. The model estimates the transmissibility reduction from breakthrough infections to 43% ([32 -- 55]% 95%-likelihood interval) and that 39,100 critical care stays ([26,100 -- 57,100] 95% confidence interval) and 47,400 ([36,200-62,800]) hospital deaths have been prevented by the French vaccination campaign by August 20 2021 -- respectively corresponding to 46% and 57% relative preventions of these outcomes. Furthermore, we show that most of the critical COVID-19 forms have been prevented by the collective component of the vaccine rather than individual prophylaxis, despite its greater effectiveness. These results are in line with the accelerating decrease in fatality ratio with vaccine coverage we highlight in worldwide data.