This is the time of year to enjoy pumpkin spiced lattes, hayrides, and apple picking, but it’s also when we should all think about our immunity. COVID-19 and the flu may both pick up speed as the weather gets colder and we move indoors. However, there’s something you can do to reduce the risk of a hospital stay. Researchers at the University of Miami Miller School of Medicine found evidence that the flu vaccine protects against severe COVID-19.
According to the study in PLoS One Journal, people who get the flu shot and then come down with COVID-19 are less likely to develop serious complications. Those include sepsis, stroke, and deep vein thrombosis. COVID-19 patients without the flu vaccine are also more likely to go to the emergency room and the ICU.
A Closer Look at COVID-19 and the Flu Vaccine
The researchers collected information for their study from 56 health care organizations. Most of the records they analyzed were from the United States. Others were from the United Kingdom, Italy, Germany, Israel, and Singapore. Overall, they analyzed 74,574 records of patients with COVID-19, making this study the largest of its kind.
The team split patients into two even groups: those who had received the flu shot and those who did not. Patients in the first group received the flu shot six months to two weeks before a COVID-19 infection set in.
The researchers then determined how many patients had serious medical complications after testing positive for COVID-19. They also marked the number of days it took to develop a serious complication in both groups. To do so, they grouped medical complications into four categories: those that developed within 30, 60, 90, and 120 days.
The researchers noticed that patients with no flu vaccination were up to 20 percent more likely to go to the ICU. They were also up to 58 percent more likely to visit the emergency department and 45 percent more likely to develop sepsis. About 58 percent were more likely to have a stroke and 40 percent more likely to develop a deep vein thrombosis. (Deep vein thrombosis is a blood clot that forms in a vein deep inside your body.) There were no links between the flu vaccine and a risk of death from COVID-19.
Why the Flu Shot Might Work
If you were surprised to hear that the flu shot could reduce your risk of severe COVID-19, you’re not alone. Researchers have been wondering about this link for some time.
“Several theories … may explain why and how the flu shot may reduce the risk of certain adverse outcomes of COVID-19,” says Dr. Benjamin Slavin, MD, co-lead author and plastic surgery resident at the University of Miami Miller School of Medicine. “One hypothesis centers around the presence of a particle in the influenza vaccine known as MF59. MF59 has been shown to help stimulate an immune response to SARS-CoV variants.”
Another theory is that the influenza vaccine activates the immune system. “Influenza vaccination’s potential protective effect may be explained by its ability to stimulate different components of the body’s innate immune system. [That is] our body’s built-in, generalized defense system against infection,” he says. “Specifically, the influenza vaccine has been shown to boost activation of natural killer cells, the levels of which have been found to be considerably decreased in moderate and severe SARS-CoV-2 cases.”
Slavin says that the flu vaccine causes your body to produce specific antibodies. Those antibodies may interact with a specific cell receptor known as the bradykinin 2 receptor. The interaction between the antibodies and this receptor may reduce inflammation. It may also boost the amount of nitric oxide in the body. A COVID-19 study published in Brain, Behavior, and Immunity — Health states that nitric oxide is a compound that helps widen blood vessels. Importantly, this compound may protect against respiratory infections.
Which shots should you get?
The research on the protective effects of the flu shot is still ongoing, but the vaccine recommendations are clear. “Regardless of whether the reason explaining the results seen in our study is because of one, some, all, or none of the reasons mentioned above, the bottom line is that we strongly recommend that everyone get both their influenza and COVID-19 vaccines this year in accordance with current CDC guidelines,” says Slavin.
“Influenza vaccination is by no means a substitute for COVID-19 vaccination … We cannot over-emphasize that the best way to protect oneself against COVID-19 is to get the COVID-19 vaccine, and to stay current with your annual flu vaccine. The CDC recently recommended getting both your flu shot and COVID-19 shot this fall. By ensuring that we are vaccinated against both viruses this flu season, we are all doing our part as a global community to keep one another safe by decreasing the risk of a possible ‘Twindemic’ that could potentially overwhelm healthcare resources.”