Why is this flu season so bad?

If this cold and flu season seem especially sneezy-coughy-fevery to you, it is not your imagination. Flu is surging in 45 states and outpatient doctor visits for flu-like symptoms are the highest they’ve been since we started keeping track of the data. 

It’s not like the flu is new: Literally every year we have to navigate cold and flu season. And yet here we are in 2026, plagued with these respiratory viruses again. What’s making this year especially difficult? 

We pose those questions to epidemiologist and science communicator Katelyn Jetelina on this week’s episode of Explain It to Me, Vox’s weekly call-in podcast. “What we typically see every winter is just this rise in respiratory viruses, whether it’s the common cold or the flu or Covid or RSV,” she told Vox. “Cold weather really causes viruses to spread very quickly and these viruses just keep mutating.”

Below is an excerpt of our conversation, edited for length and clarity. You can listen to the full episode on Apple Podcasts, Spotify, or wherever you get podcasts. If you’d like to submit a question, send an email to askvox@vox.com or call 1-800-618-8545.

Which flu viruses are circulating right now? 

Flu specifically is in a very interesting year. Epidemiologists are concerned that this year is going to be worse than previous years, and that’s because one strain of the flu called influenza A H3N2 mutated over the summer as it spread through Australia and the Southern Hemisphere. Specifically, it shifted from a J subclade to a K subclade. This is an incremental change that happened when this virus spread.

Mutations are normal for the flu. In fact, the flu is infamous for unpredictable curveballs. Flu can change in two ways: one is called a shift, which is a major overhaul that happens when two different flu viruses infect the same cell, swap genetic material, and create a new virus. This type of shift can spark a pandemic because our immune systems have never seen that version of the virus before. 

That is not what we have. What we have this winter is called a drift, and this means there’s a smaller incremental change that happens as the virus spreads. It shouldn’t trigger panic. But what it does mean is that our current vaccines will likely recognize some, but not all, of this updated virus. It’s just simply bad luck that H3N2 evolved so much in the months before this flu season really took off. Together these factors mean that the virus will be better at slipping past vaccines as well as our prior immunity. That translates into more cases and more severe disease among those at highest risk.

This makes sense. I got the flu shot and still got the flu recently. I thought I prepared myself.

You did. I want to be very clear that vaccination still matters. We’re far from powerless. The flu shot is not designed to protect against infection. It’s designed to prevent hospitalization and you dying. And given that we’re doing this interview, you didn’t die. 

Yeah!

Having the flu may still be miserable and it’s not fun, but it can help avoid the worst outcomes. 

For people who didn’t get a flu shot, is it too late now? Do they just have to wait this season out with their fingers crossed?

No, it is not too late for several reasons. One is we haven’t even reached the peak of flu yet. There’s still going to be a lot of sickness out there. Flu vaccines take about two weeks for your immune system to really kick into gear, so there’s plenty of time to still be protected. 

The other thing with flu is that there are many strains that circulate. With Covid, we were all used to one strain circulating like Delta or Omicron, but with flu, there’s two to three strains that circulate. So unfortunately what this means is that if you get infected by flu once, you could get infected by flu twice later on in this season. Getting a vaccine can help protect from those other strains as well.

What else is going around?

A lot! Viruses love this time of year, so Covid is also starting to increase. Another thing that’s circulating is RSV, which wreaks havoc among infants. We have other viruses like the common cold, and then something that is not fun at all either called norovirus, sometimes called stomach flu, which causes diarrhea and nausea. That spreads not necessarily through the respiratory tract, but through [things like] touching a dirty doorknob or eating contaminated food. So there’s plumes of viruses everywhere you’re going right now.

So if we want to boost our immune systems, what works and what doesn’t?

The rumor mill is really hot on ways to boost the immune system. For the general population, dietary supplements actually do not work in preventing or reducing severity of illness. Vitamin C or vitamin D just haven’t [been] shown to help with respiratory viruses. Or something like cold plunges: these have become increasingly popular for boosting immunity, but there’s really inconclusive evidence and a lot of conflicting studies showing whether they’re effective. Nasal breathing, saunas — a lot of these just have been tested in really small studies. 

The best thing you can do is give your immune system time to do its job. How we do that is a balanced, nutrient-dense diet. Sleep is critical. This is when the immune system executes most of its repair process. Those who are chronically sleep-deprived actually tend to get more colds than those [who] aren’t. So make sure you get a lot of sleep as well as hydration. Proper fluid balance really ensures your body can transport nutrients and immune cells and remove a lot of these pathogens and waste products.