A new study sheds light on how cold and flu viruses interact.

By Renee Cherry
December 17, 2019

Cold and flu symptoms have some overlap, and neither is pretty. But if you're unlucky enough to get hit with one, you're at least less likely to get the other simultaneously, according to a recent study. (Related: Cold Vs. Flu: What Is the Difference?)

The study, published in Proceedings of the National Academy of Sciences, explored how the flu and other respiratory viruses interact with each other. Drawing from over 44,000 cases of respiratory illness over the course of nine years, researchers set out to better understand whether having one respiratory virus affects the odds of picking up a second one.

The study authors wrote that they found "strong support" for the existence of a negative interaction between influenza A and rhinovirus (aka the common cold). In other words, once someone's attacked by one virus, they may be less susceptible to a second one. The authors offered up two possible explanations in their paper: The first is that the two viruses compete with each other for susceptible cells to attack. The other potential reason is that once infected with a virus, cells might take on a "protective antiviral state" that makes them resistant or less susceptible to the second virus. Pretty cool, no?

The researchers found a similar relationship between influenza B and adenovirus (a virus that can cause respiratory, digestive, and eye symptoms). However, this only held true at the broad population level rather than on the individual level. That might be because people who were hospitalized for one virus were then less likely to be exposed to the other during their care, the authors suggested in their research. (Related: How Long Does the Flu Usually Last?)

FYI, though: Getting the flu doesn't necessarily mean you'll have a temporary shield protecting you from all other illnesses. In fact, contracting the flu can make you more susceptible to harmful bacteria, says Norman Moore, Ph.D., director of infectious diseases scientific affairs for Abbott. "We do know that influenza can predispose people to getting secondary bacterial pneumonia," he explains. "While this study may suggest that there is less risk of contracting other viruses, it's important to remember that when people die of influenza, it is usually from a bacterial complication like pneumonia." (Related: How Easy Is It to Get Pneumonia)

And ICYWW, the typical treatment for the flu doesn't change, even in the presence of an additional respiratory virus. Antivirals are common in flu treatment, but cold treatments just ameliorate symptoms, which explains why flu tests are common and cold tests aren't really a thing, explains Moore. "There are some tests that can look at all viruses, but they are more expensive," he adds. "Finding additional respiratory viruses beyond influenza often doesn't change treatment decisions, but it's always important to officially rule out influenza, which can only be done by getting tested." (Related: The Step-By-Step Stages of a Cold—Plus How to Recover Fast)

There's no getting around the fact that the flu and colds both suck on their own. But you can at least find comfort in the possibility that they're unlikely to team up against you.

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