Flu shot may help reduce severity of COVID-19 illness, study suggests

People who received a flu shot were 24 percent less likely to test positive for COVID-19 than those who did not, according to research published Feb. 22 in the American Journal of Infection Control. 

Using patient charts from the Ann Arbor-based Michigan Medicine, researchers identified 27,201 people who tested positive for COVID-19 between Feb. 27 and July 15. Of those, 12,997 or about 48 percent had a flu shot during the prior influenza season. Among this group, 525 people contracted COVID-19, compared to 693 who did not get a flu shot. Overall, the odds of testing positive for the coronavirus were reduced by 24 percent in patients who got the flu shot versus those who didn't. 

Of those who contracted COVID-19, patients who were vaccinated against the flu also had better clinical outcomes, the findings showed. They were less likely to require hospitalization for their COVID-19 illness, with an odds ratio of 0.58. They also had a lower chance of needing mechanical ventilation and had a shorter hospital stay.

Researchers did not identify significant differences in the need for intensive care or mortality between flu vaccinated patients and unvaccinated patients with COVID-19. 

The apparent link between flu vaccination and potential protection against COVID-19 could be due to trained immunity, a process in which vaccinations activate an adaptive immune response of T-helper cells that may attack a similar antigen in the future. 

Additional studies are necessary to establish a causal relationship between the flu shot and COVID-19 susceptibility and severity, researchers said, adding that "Until COVID-19 vaccine becomes widely available, the influenza vaccine should be promoted to reduce the burden of disease during the pandemic."

To view the full findings, click here.


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