One shot, two benefits!

Doctor preparing an influenza vaccine for a patient.

To try and boost sales during the pandemic many businesses are offering two-for-one deals; buy one product get another free. Well, that might also be the case with a flu shot; get one jab and get protection from two viruses.

A new study offers an intriguing – though not yet certain – suggestion that getting a flu shot could not only reduce your risk of getting the flu, but also help reduce your risk of contracting the coronavirus. If it’s true it would be a wonderful tool for health professionals hoping to head of a twindemic of flu and COVID-19 this winter. It would also be a pretty sweet deal for the rest of us.

Researchers at Radboud University Medical Center in the Netherlands looked through their hospital’s database and compared people who got a flu shot during the previous year with people who didn’t. They found that people who got the vaccine were 39 percent less likely to have tested positive for the coronavirus than people who didn’t get the vaccine.

Now, there are a bunch of caveats about this study (published in the preprint journal MedRxiv) one of which is that it wasn’t peer reviewed. Another is that people who get flu shots might just be more health conscious than people who don’t, which means they might also be more aware of the need to wear a mask, social distance, wash their hands etc.

But that doesn’t mean this study is wrong. Two recent studies (in the journal Vaccines and the Journal of Medical Virology) also found similar findings, that people over the age of 65 who got a flu shot had a lower risk of getting COVID-19. That’s particularly important for that age group as they are the ones most likely to experience life-threatening complications from COVID-19.

But what could explain getting a two-fer from one vaccine? Well, there’s a growing body of research that points to something called “trained innate immunity”. Our bodies have two different kinds of immune system, adaptive and innate. Vaccines activate the adaptive system, causing it to develop antibodies to attack and kill a virus. But there’s also evidence these same vaccines could trigger our innate immune system to help fight off infections. So, a flu vaccine could boost your adaptive immunity against the flu, but also kick in the innate immunity against the coronavirus.

In an article in Scientific American, Ellen Foxman, an immunobiologist and clinical pathologist at the Yale School of Medicine, says that might be the case here: “There is evidence from the literature that trained immunity does exist and can offer broad protection, in unexpected ways, against other pathogens besides what the vaccine was designed against.”

The researchers in the Netherlands wanted to see if there was any evidence that what they saw in their hospital had any basis in fact. So, they devised a simple experiment. They took blood cells from healthy individuals and exposed some of the cells to the flu vaccine. After six days they exposed all the cells to the SARS-CoV-2, the virus that causes COVID-19.

Compared to the untreated cells, the cells that had been exposed to the flu vaccine produced more virus-fighting immune molecules called cytokines. These can attack the virus and help protect people early on, resulting in a milder, less dangerous infection.

All in all it’s encouraging evidence that a flu shot might help protect you against the coronavirus. And at the very least it will reduce your risk of the flu, and if there’s one thing you definitely don’t want this year it’s having to battle two life-threatening viruses at the same time.