The findings of a new study suggest that people, who received a flu shot during the last flu season, were significantly less likely to test positive for COVID-19 when the pandemic hit. Those who did test positive faced lesser complications than those who didn't receive their flu shot.

For our comprehensive coverage and latest updates on COVID-19 click here.

These new findings mean senior author Marion Hofmann Bowman, M.D., is continuing to recommend the flu shot to her patients even as the flu season may be winding down. "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 Hofmann, an associate professor of internal medicine and a cardiologist at Michigan Medicine Frankel Cardiovascular Centre. Michigan Medicine is the academic medical centre of the University of Michigan.

Researchers reviewed medical charts for more than 27,000 patients who were tested for COVID-19 infection at Michigan Medicine between March and mid-July of 2020. Of the nearly 13,000 who got a flu shot in the previous year, four per cent tested positive for COVID-19. Of the 14,000 who hadn't gotten a flu shot, nearly five per cent tested positive for COVID-19. The association remained significant after controlling for other variables including ethnicity, race, gender, age, BMI, smoking status and many comorbid conditions, Hofmann says.

People who received their flu shot were also significantly less likely to require hospitalisation, although the researchers didn't find a significant difference in mortality between the two groups. No one in the study tested positive for both infections at the same time. The underlying mechanism behind the association isn't yet clear, Hofmann says. "It is possible that patients who receive their flu vaccine are also people who are practising 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", she says.

Prospective longitudinal studies to examine the effect of the flu vaccine on respiratory illness are ongoing, including the Household Influenza Vaccine Evaluation (HIVE) study through the University of Michigan's School of Public Health. "It's powerful to give providers another tool to encourage their patients to take advantage of available, effective, safe immunisations," says co-first author Carmel Ashur, M.D., M.S., an assistant professor of internal medicine and a hospitalist at Michigan Medicine.

Months ago, Hofmann was concerned about misinformation she kept seeing online that connected the flu vaccine with a COVID-19 infection. "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", she says.

Before the pandemic hit, Hofmann and co-first author Anna Conlon, PhD, a U-M Medical School student, educated Frankel CVC patients about another encouraging association with the flu vaccine: cardiovascular protective effects.

"There is robust data that the flu shot prevents heart attack and hospitalisations for heart failure, which is an additional reason to get your vaccine every flu season", Conlon says.