CDC: Signs point to an early start for flu season, with cases already ticking up in parts of the U.S.

Before the Covid-19 pandemic emerged, influenza trackers would begin reading tea leaves around this time of the year, looking for signs of whether there would be an early start to the flu season in the northern hemisphere and which of the various flu viruses might be responsible for the most cases over the coming winter.

Flu transmission has been low since the start of the pandemic, but an odd spurt of activity in April, May, and even early June of 2022 — which coincided with the onset of an early and robust flu season in Australia — suggests that flu may be making its way back.

In fact, the influenza trackers at the U.S. Centers for Disease Control and Prevention are seeing signs that flu activity is picking up in parts of the country. STAT talked on Friday with Lynnette Brammer, a flu epidemiologist and team lead for domestic surveillance in the CDC’s influenza division, to get a sense of what the agency is seeing.

The transcript of that conversation has been lightly edited for clarity and length.

The week before last — the week ending Oct. 8 — was the first week of the 2022-2023 flu reporting season. The CDC posted its first update for the new season on Friday, Oct. 14. The percentage of flu tests that were positive has been ticking up for the past few weeks. Is the CDC detecting signs that we might see an early start to the flu season?

I think we are. Nationally, flu positivity in the clinical labs last week was 3.3%, but it was over 10% in the Southeast. And in the South Central region, it was 5%. Flu hospitalizations are going up. And they’re going up in the same places where flu positivity is going up and ILIs [influenza-like illnesses] are going up.

All the pieces are sort of falling into place, and you’re getting sort of a consistent picture in the Southeast and maybe in South Central, and it’s probably spreading out.

So things are starting to bubble. I’ve been waiting to get my flu shot till it seemed like transmission was picking up. Maybe I should start thinking about booking it?

I went and got mine last week. And I usually wait a little bit later. But living here in the Southeast, I thought it was time.

People have been suggesting we’re in for a bad flu season because Australia had quite a lot of flu in its winter of 2022. Folks are looking at what happened in Australia and suggesting we’re following them. But one could argue that their early season seemed to follow our late surge of cases in the spring.

Australia’s flu season was a little bit earlier than normal. They had a lot of cases reported, but they did a lot of testing. And it was the H3N2 virus. Same as here.

I think things are just trying to get back into this kind of normal pattern of respiratory illness following the Covid pandemic. And things are not exactly back in sync yet. In South America, some of their activity has sort of been out of sync. I think it was Argentina — timing-wise, their activity looked more like northern hemisphere activity than southern hemisphere activity. Again, I think it’s just everything’s falling back into its place and things are starting to happen, just not always exactly at the same time you would expect them to.

So Australia was a little bit early. You could say Argentina was either very late or very early.

Did they have much flu activity?

I’m not very good at judging exactly how severe it was or how much there was, just because testing practices have changed so much because of the Covid pandemic that it’s really hard to say.

Even with our own data, it’s harder to interpret because you’ve got another virus in the mix. So it’s a little more difficult to interpret our surveillance data. And for me, it’s even much more difficult to interpret somebody else’s surveillance data.

I was emailing a while back with Kanta Subbarao, who heads the World Health Organization’s influenza collaborating center in Australia. She told me that they’d had quite an active season in 2022, but that a lot of the activity was in kids. I’m not suggesting that’s not important, but when we think about H3N2, we normally think about old people dying.

And that’s very similar to what we saw in the U.S. last year. Our H3 activity — we didn’t see a lot of it in the elderly. It was mostly in younger people. Why that is, I’m not sure. Maybe the elderly are still being more cautious and not shedding the Covid mitigation measures quite as quickly as other age groups.

Thinking about this flu season and what you’re seeing so far, what’s your best guess for what’s ahead?

Our syndromic surveillance methods are much trickier to try and interpret now, with Covid in the picture. It just muddies the water, basically.

We’ll have to see if the flu and Covid circulate at the same time. Right now, it looks like Covid is still trending down in a lot of the country, but flu’s going up in a lot of the country.

If individuals start to feel crappy this winter, how will they know if it’s a cold? Flu? Covid?

I think testing is going to be really important given that, for flu and Covid, there are treatments that — particularly for high-risk people — can make a huge difference in how well they are able to get through their illness. So it’s going to be really important to test so physicians can know the appropriate treatment for their patients.

That’s going to require behavior change, won’t it? Prior to the pandemic, most people who got sick with an influenza-like illness didn’t get tested, unless they were proactive about trying to see if they had influenza to get Tamiflu or one of the other flu antivirals.

A lot of people still won’t be tested. They may test themselves at home for Covid. And either they’ll think, well, if I’m negative for Covid, I’m negative for Covid. But they may not go on to get a flu test.

And maybe that’s okay if you’re not somebody who would benefit much from an antiviral medication. But for people who are at high risk, I think they would have gone in for a flu test before. I’m hoping they still will.

It would be great to be able to do a home test that would tell you if you had Covid or flu or some other respiratory bug. Is that in our future?

I don’t know what’s coming down the road there. But I know that people are thinking about at-home testing for flu.

One of the kinds of flu viruses — the Yamagata lineage of influenza B — hasn’t been seen since March of 2020. When do you think the flu world is going to feel comfortable saying that B/Yamagata is gone?

I think it will be a little while longer.

But do you think it’s gone?

I think there’s a good chance that it’s gone. But I’m not 100% confident. And the reason I say that is back in the 1990s, B/Victoria stopped circulating everywhere except China. And it just sort of hung out there for most of the 1990s. It was a really odd situation. China would share viruses and it was there, and they would have pretty good outbreaks with it. But it never moved. And then, at the beginning of the 2000s, it did. And it came back [globally].

If B/Yamagata is somewhere where it has less visibility, with less lineage testing and less sequencing data, it could be still sitting there and reemerge. So it’ll be a little while, I think, before people are really confident to say yes, B/Yamagata is really gone.

I’m sure you’ve been working on things in the past couple of years that weren’t related to flu. As a flu person, are you kind of excited to contemplate the return of flu, or are you dreading it?

It’s good to get back to a pathogen you know. I feel a lot more comfortable talking about the flu.

In the coming winter or two, it’s going to be fascinating to see how things play out with these pathogens, to see what happens when viruses that were suppressed in the pandemic resume their normal positions again. Do they divide up the winter season? Do they strike at the same time?

Yeah, it’s going to be really interesting to see how everything falls into place now that there’s another major player in the respiratory virus field. To see if they push each other around, if seasonality stays the same or if it shifts. And it will be interesting to see if people respond differently now.

Are you hopeful they will?

Maybe. Maybe people will be more likely to stay home when they’re sick. Or be more likely to do simple things to protect themselves at times when there’s a lot of flu circulating. Maybe for some people wearing a mask is now not as odd as it was before the Covid pandemic. Masks seemed to help a lot with the flu.