As more people got the COVID-19 vaccine, masks came off and socializing began again, quite a few people experienced the return of runny noses and sneezes this summer.

Coronavirus precautions have kept many away from other viruses like colds and flu since the pandemic began. Dr. Helen Chu, a physician with the University of Washington Medicine, says her team in Seattle has been surveilling viruses popping up this summer.

She’s particularly concerned about respiratory syncytial virus (RSV), which causes pneumonia in babies and young children. The contagious virus came back raging in the warmer months, she says.

Other viruses that normally arise in the fall and winter months, such as parainfluenza and human metapneumovirus, returned this summer, she says.

Human factors — mask requirements being halted, kids going back to school, and an uptick in traveling and socializing — revitalized the return and spread of these viruses, she says.

It’s also about human immune systems too, Chu says. In pandemic lockdown, many people were not exposed to viruses the same way they were before in communal settings. If humans are exposed to some of these germs on a regular basis, immune systems are more susceptible to them, she explains.

“Generally, when we see a virus over and over again every year, it boosts our immune response to that virus even if we don’t get very sick, and this is particularly the case in adults and older children,” she says. “For the very young children who never saw these viruses, now haven’t seen the flu and haven’t seen RSV at all, they are going to see it for the first time.”

She worries there’s potential for a large group of very young children to have no immunity to some common viruses. “A lot of them will be seeing it for the first time, twice the number that we normally would expect,” she says.

And even those who are partially immune to flu, for example, will be vulnerable to getting sicker, she says.

Influenza is “unpredictable,” she says. The flu often mutates as it spreads from person to person, but pandemic precautions have caused low circulation of these mutations.

“It could be that what’s going to come back is not going to be something that’s going to make us very sick. But we don’t know,” she says. “And we also don’t know how to design a flu vaccine right now because we don’t have the viruses from the last season to really use to help us pick what to put in the vaccine.”

Still, the best protection against influenza is getting the flu vaccine, Chu says. While the amount of protection is unknown, the vaccine will provide “some degree of protection against flu that’s circulating,” she says.

Pre-pandemic flu vaccination numbers weren’t very high, she says. She’s worried COVID-19 vaccine hesitancy and a general decrease in childhood vaccination rates over the course of the pandemic will spill over into public discourse surrounding the flu vaccine.

Chu advises to get the flu vaccine, continue to stay home when sick, properly wash hands and wear a mask to avoid coming down with a cold or flu.

 Julia Corcoran produced and edited this interview for broadcast with Todd Mundt. Serena McMahon adapted it for the web.

This article was originally published on WBUR.org.

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