evaluation of the possible effect of the influenza vaccine on the severity, mortality, and length of hospitalization among unvaccinated covid-19 patients; an observational, cross-sectional study

Background: based upon who (world health organization) coronavirus dashboard more than 5 million deaths worldwide have been attributed to the covid-19 (coronavirus disease 2019) caused by the sars-cov-2 virus (severe acute respiratory syndrome coronavirus) till november 2021. the annual flu vaccination has raised many questions about the vaccine’s effects on covid-19 outcomes. several possible mechanisms including cross-reactivity and cross-protection have been reported to be responsible for the potential protective effect of the flu vaccine on the covid-19 infection. this study was performed to evaluate the possible effect of the influenza vaccine on the disease severity, the mortality rate, and the length of hospitalization in covid-19 patients.methods: the data of 1300 patients were recorded from may 2020 to october 2020. patients with a previous history of covid-19, patients under 18 years old, and patients who did not have accurate information about their influenza vaccination history were excluded. 498 hospitalized unvaccinated covid-19 patients with typical clinical manifestations and a positive pcr (polymerase chain reaction) test for covid-19 were included in this observational, cross-sectional study. the participants were divided into two groups (vaccinated and unvaccinated) based on the history of influenza vaccination at the time of admission.results: the length of hospital stay was lower in the vaccinated compared to the unvaccinated group (p < 0.05). however, there was no significant difference between the mortality rate, the need for icu (intensive care unit) admission, and the severity of the disease between the two groups (p> 0.05).conclusion: since the patients studied in this article did not receive any of the covid-19 vaccines; therefore, the effect of influenza vaccination on the clinical course of covid-19 can be evaluated using the results of this study. a longer length of hospital stay was observed in the unvaccinated patients in our study, which may suggest the possible protective effect of the influenza vaccine against covid-19.