Does Influenza Vaccination Reduce the Risk of Contracting COVID-19?

Abstract

The concurrent timing of the COVID-19 pandemic and the seasonal occurrence of influenza, makes it especially important to analyze the possible effect of the influenza vaccine on the risk of contracting COVID-19, or in reducing the complications caused by both diseases, especially in vulnerable populations. There is very little scientific information on the possible protective role of the influenza vaccine against the risk of contracting COVID-19, particularly in groups at high-risk of influenza complications. Reducing the risk of contracting COVID-19 in high-risk patients (those with a higher risk of infection, complications, and death) is essential to improve public well-being and to reduce hospital pressure and the collapse of primary health centers. Apart from overlapping in time, COVID-19 and flu share common aspects of transmission, so that measures to protect against flu might be effective in reducing the risk of contracting COVID-19. In this study, we conclude that the risk of contracting COVID-19 is reduced if patients are vaccinated against flu, but the reduction is small (0.22%) and therefore not clinically important. When this reduction is analysed based on the risk factor suffered by the patient, statistically significant differences have been obtained for patients with cardiovascular problems, diabetics, chronic lung and chronic kidney disease; in all four cases the reduction in the risk of contagion does not reach 1%. It is worth highlighting the behaviour that is completely different from the rest of the data for institutionalized patients. The data for these patients does not suggest a reduction in the risk of contagion for patients vaccinated against the flu, but rather the opposite, a significant increase of 6%. Socioeconomic conditions, as measured by the MEDEA deprivation index, explain increases in the risk of contracting COVID-19, and awareness campaigns should be increased to boost vaccination programs.

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

“…Since influenza almost disappeared during the 2020 season 17–23 and thus the prevention of co‐infection could not explain this possible protective effect of the influenza vaccination on COVID‐19, it was hypothesized that influenza vaccination directly played protective roles against SARS‐CoV‐2 infection. The ensuing studies on the association between influenza vaccination and SARS‐CoV‐2 infection and COVID‐19 severity were the basis for this meta‐analysis 38–88 …”

“…The reason for exclusion of other trials was specified (lack of details, no controls, Figure 1). In total: 51 studies, 33 studies for infection (with 37 comparison arms), 38–70 14 studies (with 14 comparison arms) for hospitalization, 43,46,53,54,57,69,71–78 11 studies (with 11 comparison arms) for admission to ICU, 42,53,54,73,77–79 and 19 studies (with 20 comparison arms) for mortality 43,53,57,61,69,75–78,80–88 fulfilled the inclusion criteria. Tables 1A,B,C,D show details of studies included in this meta‐analysis.…”