Study finds flu vaccines reduced risk of infection and severe illness from COVID-19

Even before there was a COVID-19 vaccine, vaccines used against influenza apparently provided some protection against COVID-19 infection and were helpful in preventing severe cases of COVID-19, at least for a few weeks after the vaccine, according to a preprint of a study that focused on health care workers in Qatar.

The study involved review of the national health databases for COVID-19 testing, flu vaccination, hospitalization and death records of 30,774 health care workers in Qatar between Sept. 17-Dec. 31, 2020, before introduction of COVID-19 vaccination. The authors said they focused on health care workers, because it can be assumed that factors such as health awareness, prevention and risk for members of this group were relatively similar.

“Recent influenza vaccination was associated with a 30% reduction in the risk of SARS-CoV-2 infection by the original virus, before introduction of variants of concern. Recent influenza vaccination was also associated with a 90% reduction in the risk of severe COVID-19,” the study’s authors reported. “Incidence of severe COVID-19 was rare among those vaccinated, with only one case of severe COVID-19 documented among them.”

The findings corroborate other studies that found similar effects for influenza vaccination, the authors noted.

“These findings may be explained by influenza vaccination triggering a nonspecific immune activation, or trained or bystander immunity that is protective against SARS-CoV-2 infection,” the authors said.

The study only looked at those who had recently had an influenza vaccine.

“Given that nonspecific immune activation may not last beyond a few weeks, and in context of the relatively rapid waning of COVID-19 vaccine immunity, the observed effectiveness of influenza vaccination is likely short lived,” the authors said.

Nonetheless, they added, it shows that the benefits of an influenza vaccine extend beyond simple protection against the flu.