Flu Shot Linked With Less Severe Cases of COVID-19

A recent study conducted by investigators from the University of Michigan has discovered that those who received a flu shot last season were significantly less likely to test positive for an infection with COVID-19. Results from the study were published in the American Journal of Infection Control.

"It's powerful to give providers another tool to encourage their patients to take advantage of available, effective, safe immunizations," Carmel Ashur, a co-first author on the study said.

For the study, the investigators reviewed more than 27,000 medical charts from patients who were tested for COVID-19 between March and July of 2020. Of those, 13,000 received a flu shot the previous year and 14,000 did not receive one.

Findings showed that of those who did get the flu shot, 4% tested positive for COVID-19, compared to 5% of those who did not receive the flu vaccine the previous year. After controlling for variables including gender, race, ethnicity, age, smoking status and BMI, the association remained significant.

Though these results are promising, the mechanism underlying the association is not yet fully clear.

"It is possible that patients who receive their flu vaccine are also people who are practicing more social distancing and following CDC guidelines,” Marion Hofmann Bowman, senior author on the study said. “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."

Prospective longitudinal studies that are looking to examine the effect of the flu vaccine on respiratory illness are currently ongoing, including the Household Influenza Vaccine Evaluation (HIVE) study through the University of Michigan's School of Public Health.

"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," Hofmann said.