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Flu Bug: Missing In Action

Ramon Maldonado-Cardenas grimaces as he gets a flu shot from pharmacy student Khoa Truong during a health fair in Sacramento, Calif., last October.
Rich Pedroncelli
Ramon Maldonado-Cardenas grimaces as he gets a flu shot from pharmacy student Khoa Truong during a health fair in Sacramento, Calif., last October.

It's been a weird winter. It's warm when it should be cold. There's mud where there should be snow. Flowers are blooming way ahead of schedule. Wildlife seems confused.

Well, here's one more weirdness: The flu seasonseems to be largely M.I.A.

If this were a typical year, you'd look around and see lots of people feeling pretty miserable. "Flu season usually kicks off in a big way in late December early January," says Lyn Finelli, of the federal Centers for Disease Control and Prevention in Atlanta. "It peaks at the end of February or the beginning of March and we usually have influenza around until May."

But not this year. In the 29 years since the CDC started tracking the flu, this is the slowest start to a flu season ever, she says.

In lots of places around the country, the flu is simply nowhere to be found. Take Nashville, Tenn., for example. "We've been looking hard for influenza and it's as though it were July. We can't find any," flu specialist Vanderbilt University's Dr. William Schaffner says.

So what's going on? Well, the weirdly warm weather could be playing a part, according to the CDC's Finelli. "We know that influenza virus survives best in cool and dry conditions," Finelli said.

And the better the flu virus survives, the better the chances it can infect someone. Plus, when it's cold outside, people tend to spend more time inside, where they're more likely to come close to someone who's infected.

"We have large groups of people congregating in one place and transmission may take place a little bit more effectively in that situation," she said.

But Finelli and Schaffner think two other factors may be playing a bigger role. One is that the main flu viruses out there this year have been around for a year or two. So a lot of people have already been exposed to them and have built up natural immunity.

At the same time, lots of people have gotten their flu shots. By November, more than 36 percent of Americans had gotten vaccinated, up from less than 33 percent a year earlier.

"The combination of natural infections which give you some immunity as well as widespread vaccination, I think we have a very well-protected population at the moment," Schaffner says.

That doesn't mean no one's getting sick this winter. Flu seems to be really starting to pick up in some parts of the country, such as California. And there's still lots of cold and other bugs circulating. But there's a lot less flu than usual.

"Fewer people have been sick, fewer doctor visits, fewer people have to be in the hospital, fewer deaths due to influenza. So we'll take that, that's all a great post-Christmas present for us," Schaffner says.

But what does this all mean for the future? The simple answer: No one knows. The flu season could just be a dud. Or it could suddenly take off.

"It could be that influenza will now start to rev up and we could have a big March of influenza which will be rather late going into April," Schaffner says.

Whatever happens this year, there's always next year. The flu viruses could mutate, making a lot more people sick. Or a really nasty flu virus could suddenly emerge, causing lots of suffering. Or, it could just be another dud.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Rob Stein is a correspondent and senior editor on NPR's science desk.