A new study has found an intriguing association between people who received a flu shot in the 2019/2020 flu season and COVID-19. When the pandemic hit, these people were less likely to test positive for the disease, and those who did get it had on average few complications compared to the people who had not taken the vaccine.
The work is published in the American Journal of Infection Control and looked at 27,201 people who were tested for COVID-19 by July 2020. Of those, 1,218 people tested positive for COVID-19. When the people sampled were divided into those who received a flu vaccine in the year before and who hadn’t, the team found a difference.
Of those who received a flu vaccine, 4 percent tested positive for COVID-19, while the fraction that didn’t receive it was higher at 4.9 percent. The team controlled for variables such as ethnic background, gender, age, as well as health-related factors such as smoking. The difference is small in absolute terms, but quite high in relative terms. It means that patients were 24 percent less likely to test positive for COVID if they had their flu shot.
The team also showed that people who received their flu shot were also less likely to require hospitalization compared to those that did not. It is unclear at this stage if the cause for this association is biological (the flu vaccine somehow prepares the immune system against a different type of virus) or if it is social.
“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,” senior author Professor Marion Hofmann Bowman, from the Michigan Medicine Frankel Cardiovascular Center, said in a statement.
The possible association is welcome news, as misinformation was spreading last year that flu vaccines were falsely connected to COVID-19 infections. This work shows that the opposite is the case, with the flu vaccine actually leading to better health outcomes when it comes to the pandemic.
“It’s powerful to give providers another tool to encourage their patients to take advantage of available, effective, safe immunizations,” added co-first author Professor Carmel Ashur from Michigan Medicine.
Previous work showed a positive association between the flu vaccine and the prevention of heart attacks and hospitalization related to heart failures. Really great news all around for flu vaccines!