Why the flu season is so bad and how you can protect yourself

Amna Nawaz:

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.

William Brangham:

That's right, Amna.

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 seven 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 percent 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 Pekosz. He's a virologist at Johns Hopkins Bloomberg School of Public Health.

Andrew Pekosz, thank you so much for being here.

We know flu is a shape-shifter. 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?

Andrew Pekosz, Johns Hopkins University:

Yes, well, the first thing we know about this subclade K virus, which is part of a larger group of viruses we call H3N2 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, it also has changed based on the vaccine that was distributed earlier this fall and 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 preexisting immunity in the population that is induced by either infection or by vaccination.

William Brangham:

So is that why we are hearing reports that the current flu shot that people can get at the drugstore is considered not as effective against this particular strain?

Andrew Pekosz:

Yes, this year is what we call a mismatch between the vaccine strain and the circulating virus.

We know there's a few mutations that will cause some of that vaccine-induced immunity to not recognize the currently circulating virus. And what usually results from that is, we end up seeing a drop in the vaccine efficacy, particularly against infection.

Now, it's important to note that, even in a year when there's a mismatch of this sort, we oftentimes still see a signal of protection against severe disease that's associated with vaccination. So just because there's a mismatch in this clade K virus doesn't mean you shouldn't take the vaccine. If you haven't gotten the vaccine already, still a good idea to take it.

William Brangham:

It's still -- there's still time to get some protection out of it for the rest of this season?

Andrew Pekosz:

Yes, the influenza vaccine takes about two weeks for you to generate a strong immune response to it. Flu seasons usually last anywhere from four to six weeks or longer.

So, even if you're in a part of the country that's starting to experience a rise in influenza cases, not a bad idea to go get vaccinated because it'll protect you against the tail end of the flu season.

William Brangham:

I want to ask you a question about public health messaging.

Recently, Dr. Mehmet Oz, who runs the Center for Medicare and Medicaid Services, one of the most prominent doctors in the Trump administration, was on TV and he was asked about flu prevention. And he ticked off a whole slew of things that people should do, getting more exercise, getting more sunlight, eating well, taking vitamin D, sneezing into your elbow.

The only thing he said about the vaccine, the flu shot, was something like, we know it doesn't always work that well and it's controversial.

What do you make of that as a messaging strategy?

Andrew Pekosz:

Well, certainly, the healthier that you are, the better are you will be at fighting off an infection.

But there's nothing really controversial about the influenza vaccine. We know that it works. We know that it's safe. It does vary from year to year in terms of its efficacy. But that's primarily because we have to choose a flu vaccine six to nine months before our flu season in order to have enough time to manufacture enough vaccine to distribute.

And with this clade K variant, for instance, it emerged after the vaccine was chosen for the Northern Hemisphere last February. So there really was no chance for us to make a better matched flu vaccine because of that -- manufacturing issues.

So, again, the vaccine works. It could be better, but certainly it works. And there's no reason why most individuals shouldn't take the influenza vaccine.

William Brangham:

So who is most at risk from this flu right now?

Andrew Pekosz:

Well, everyone can get infected, but, when it comes to that severe disease, we're seeing a typical pattern, which is, individual -- young individuals, pediatric populations, kids under the age of 11, are one prime area that is suffering from severe disease.

And then individuals over the age of 65 are also suffering from more severe disease. Now, it's important to note that right now the data is saying that we're seeing a lot of flu cases and a proportionate rise in the amount of severe cases. So, we're not seeing any data so far that says the clade K variant is more dangerous to people than other H3N2 viruses that we have seen.

It's just that more people are susceptible. And, therefore, we will be seeing more cases and a corresponding or proportionate rise in the number of severe cases.

William Brangham:

Do we know why some areas seem to be having bigger outbreaks than others?

Andrew Pekosz:

Yes, we think that, every year, influenza, particularly here in the U.S., it appears in different states at slightly different times of the year. New York was unfortunate to be one of the first states that really got hit by this clade K virus, and so we have seen the most experience in the U.S. in New York in terms of how quickly that virus can spread and how many cases it can cause.

Over the last two weeks, we have seen many states that have gone from basically no cases or very few cases to a very high number of cases. And we will probably see the rest of the country see the same thing over the next two weeks or so. So it's not uncommon to see influenza appear in different states at different times.

Sometimes, that's just bad luck. That's where the virus lands first and starts spreading first. And then it moves from that area into other parts of the country.

William Brangham:

All right, that is Andrew Pekosz of Johns Hopkins Bloomberg School of Public Health.

Thank you so much for being here.

Andrew Pekosz:

My pleasure.