Vaccination against influenza viruses reduces infection, not hospitalization or death, from respiratory COVID‐19: A systematic review and meta‐analysis

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) causes COVID‐19 and has brought a huge burden in terms of human lives. Strict social distance and influenza vaccination have been recommended to avoid co‐infections between influenza viruses and SARS‐CoV‐2. Scattered reports suggested a protective effect of influenza vaccine on COVID‐19 development and severity. We analyzed 51 studies on the capacity of influenza vaccination to affect infection with SARS‐CoV‐2, hospitalization, admission to Intensive Care Units (ICU), and mortality. All subjects taken into consideration did not receive any anti‐SARS‐CoV‐2 vaccine, although their status with respect to previous infections with SARS‐CoV‐2 is not known. Comparison between vaccinated and not‐vaccinated subjects for each of the four endpoints was expressed as odds ratio (OR), with 95% confidence intervals (CIs); all analyses were performed by DerSimonian and Laird model, and Hartung‐Knapp model when studies were less than 10. In a total of 61 029 936 subjects from 33 studies, influenza vaccination reduced frequency of SARS‐CoV‐2 infection [OR plus 95% CI = 0.70 (0.65−0.77)]. The effect was significant in all studies together, in health care workers and in the general population; distance from influenza vaccination and the type of vaccine were also of importance. In 98 174 subjects from 11 studies, frequency of ICU admission was reduced with influenza vaccination [OR (95% CI) = 0.71 (0.54−0.94)]; the effect was significant in all studies together, in pregnant women and in hospitalized subjects. In contrast, in 4 737 328 subjects from 14 studies hospitalization was not modified [OR (95% CI) = 1.05 (0.82−1.35)], and in 4 139 660 subjects from 19 studies, mortality was not modified [OR (95% CI) = 0.76 (0.26−2.20)]. Our study emphasizes the importance of influenza vaccination in the protection against SARS‐CoV‐2 infection.