Flu shots linked to fewer and less severe COVID-19 cases

ANN ARBOR, Mich. — University of Michigan researchers have good news for people getting flu shots this year? There’s a chance it’s giving you an added bonus — protection against COVID-19. A new study finds people receiving flu vaccinations are significantly less likely to test positive for coronavirus. Moreover, if a flu shot recipient does contract COVID, researchers say they have better odds of avoiding serious symptoms.

“It’s particularly relevant for vaccine hesitance, and maybe taking the flu shot this year can ease some angst about the new COVID-19 vaccine,” says senior study author Marion Hofmann Bowman, M.D., an associate professor of internal medicine and a cardiologist at the Michigan Medicine Frankel Cardiovascular Center, in a university release.

Study authors assessed medical data on over 27,000 people tested for COVID-19 at Michigan Medicine between March and July 2020. Among that group, 13,000 received the annual influenza vaccine during the prior flu season. Four percent of those vaccine recipients tested positive for COVID. Conversely, around five percent of the unvaccinated group had a positive test.

These findings remained consistent even after accounting for various other factors such as race, gender, age, BMI, and ethnicity.

Will a flu shot keep you out of the hospital?

Results reveal people getting the flu vaccine also have a significantly lower risk of hospitalization due to COVID. Despite those findings, researchers did not find a noticeable difference in mortality rate between the vaccinated and unvaccinated patients.

“It is possible that patients who receive their flu vaccine are also people who are practicing more social distancing and following CDC guidelines. However, it is also plausible that there could be a direct biological effect of the flu vaccine on the immune system relevant for the fight against SARS-CoV-2 virus,” Dr. Hofmann says.

Currently, Michigan researchers are conducting multiple studies to determine the full effect of the flu vaccine on respiratory illnesses in general.

“It’s powerful to give providers another tool to encourage their patients to take advantage of available, effective, safe immunizations,” says Carmel Ashur, M.D., M.S., an assistant professor of internal medicine and a hospitalist at Michigan Medicine.

Dr. Hofmann adds she was concerned a few months ago by a number of conspiracy theories linking the flu vaccine to greater COVID risk. She knew her work could help put some of those concerns to rest.

“Instead of a concerning connection between COVID-19 and the flu shot, our publication provides more confidence that getting your flu shot is associated with staying out of the hospital for COVID-19,” the study co-author says.

If all this still isn’t enough to convince you a flu shot is a good idea, researchers point out the flu vaccine also has a link to protective cardiovascular effects.

“There’s robust data that the flu shot prevents heart attack and hospitalizations for heart failure, which is an additional reason to get your vaccine every flu season,” concludes Anna Conlon, Ph.D., a U-M Medical School student.

The study appears in the American Journal of Infection Control.