You're listening to Shortwave from NPR.

Hey everybody, Maddie Sifai here with Shortwave Reporter Emily Kwong.

Hey oh, so today we have a listener questions episode.

Woop, woop, I genuinely love trying to answer all of your questions.

And this one is all about influenza, aka the flu.

The flu infects a lot of people every year.

It's hard to say just how many but according to the CDC's current estimate

between 37 and 43 million people in the United States got infected last flu season.

Wow.

That's roughly the population of the entire state of California.

Right, and year after year we have this battle with the flu.

And that's partially because there are a lot of flu viruses out there

and they are constantly changing.

So here's how that works.

When the flu makes little copies of itself, which it does over and over really fast,

there can be mutations in their DNA that can kind of change the virus enough

that our bodies can't recognize it anymore.

Or a vaccine doesn't work against it.

And that's one of the reasons why we have to get the flu vaccine every single year.

There's constantly this changing of flu viruses that render people over time

susceptible to getting reinfected.

So it's sort of like evolution on a really fast scale.

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