We are entering peak flu season, and a new flu variant known as subclade K is spreading quickly across the country, driving a sharp rise in illness and hospitalizations.

Public health officials say this current wave may last for weeks to come. William Brangham has the latest.

That's right. Omna, just this week, according to the CDC, flu activity is high or very

high in 32 states and jurisdictions. That's nearly double from the week before. More than 7 million

people nationwide have been infected, and over 3,000 have died so far this season. Only about a quarter of adults and just 17% of

children have received the flu shot as of November. So for more on the variant and what to look

out for this flu season, I'm joined by Andrew Peckosch. He's a virologist at Johns Hopkins

Bloomberg School of Public Health.

Andrew Prakash, thank you so much for being here.

We know flu is a shapeshifter.

It's why we have to design a new vaccine every single year.

But this particular strain, this subclade K, is proving to be quite a challenge.

Tell us a little bit about it. Is it more contagious? Is it more dangerous? Yeah, well, the first thing we know about this subclade K virus, which is part of a

larger group of viruses we call H3 and 2 viruses, is we know that it has mutations at a couple of what I call hot spots

on the virus that are the targets of your immune system and that can generate those protective

antibodies that minimize infection and disease. So this clade K virus has changed from the viruses

that circulated last year, and importantly,

that it also has changed based on the vaccine that was distributed earlier this fall in this

is still available.

So we think that the first thing that's going on with this clade-K virus is more people are susceptible

because it's found a way to evade that pre-existing immunity in the

population that is induced by either infection or by vaccination. So is that why we are hearing reports

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