Impact of vaccination against severe COVID-19 in the French population aged 50 years and above: a retrospective population-based study

Abstract

Background: Given the widespread implementation of COVID-19 vaccination to mitigate the pandemic from the end of 2020, it is important to retrospectively evaluate its impact, in particular by quantifying the number of severe outcomes prevented through vaccination.

Methods: We estimated the number of hospitalizations, intensive care unit (ICU) admissions and deaths directly averted by vaccination in France, in people aged ≥ 50 years, from December 2020 to March 2022, based on (1) the number of observed events, (2) vaccination coverage, and (3) vaccine effectiveness. We accounted for the effect of primary vaccination and the first booster dose, the circulating variants, the age groups, and the waning of vaccine-induced protection over time.

Results: An estimated 480,150 (95% CI: 260,072-582,516) hospitalizations, 132,156 (50,409-157,767) ICU admissions and 125,376 (53,792-152,037) deaths were directly averted by vaccination in people aged ≥ 50 years, which corresponds to a reduction of 63.2% (48.2-67.6), 68.7% (45.6-72.4) and 62.7% (41.9-67.1) respectively, compared to what would have been expected without vaccination over the study period. An estimated 5852 (2285-6853) deaths were directly averted among the 50-59 years old, 16,837 (6568-19,473) among the 60-69 years old, 32,136 (13,651-36,758) among the 70-79 years old and 70,551 (31,288-88,953) among the ≥ 80 years old.

Conclusions: The vaccination campaign in France considerably reduced COVID-19 morbidity and mortality, as well as stress on the healthcare system.

Keywords: Burden; COVID-19; Hospitalization; Impact; Mortality; Vaccination.

Fig. 1

Number of observed COVID-19 events by age and variant: A hospitalizations by age, B intensive care unit (ICU) admissions by age, C deaths by age, D reconstructed hospitalizations by variant, E reconstructed ICU admissions by variant, F reconstructed deaths by variant. *At the beginning of the time period, for simplification purposes, all cases were attributed to the Alpha variant although the historical strain was still circulating (see Additional file 1: Text S2)

Fig. 2

Values of vaccine effectiveness against hospitalizations (A) and ICU admissions and deaths (B), by dose, age and variant, according to the time since vaccination, that were used in our study. Estimations extracted from sources described in the “Methods” section (Tables S1, S2 and S3) were combined, smoothed and extended over time based on a linear decay (Methods)

Fig. 3

Cumulative numbers of A hospitalizations, B ICU admissions and C deaths observed and expected without vaccination, in the French population aged 50 years and above, from week 53–2020 to week 9–2022. Dashed lines show the 95% confidence intervals of the cumulative numbers of expected events. Non-cumulative curves are shown in Additional file 1: Fig. S3