On the ground with KPWHRI’s flu trackers

Researchers Karen Wernli and Erika Kiniry share insights on an exceptional 2024-2025 flu season

This has been a particularly rough flu season. The Centers for Disease Control and Prevention (CDC) has rated the season’s severity as “high,” and preliminary estimates suggest it is the worst season for flu cases and hospitalizations in 15 years.

Understanding the reasons why this flu season has been so intense will take time (after all, the season isn’t over yet). In the meantime, researchers have reported on one piece of the puzzle: An interim assessment shows the 2024-2025 flu vaccine has performed well, substantially reducing the risk of flu-related medical visits and hospitalizations for all age groups. However, less than half of adults and children nationwide have gotten the vaccine.

These findings are the result of the diligent work of flu-tracking researchers across the country. In Western Washington, this role is filled by scientists at Kaiser Permanente Washington Health Research Institute (KPWHRI). Since 2011, KPWHRI has been part of the CDC’s U.S. Influenza Vaccine Effectiveness (Flu VE) network — one of four networks monitoring the trajectory of each flu season and the effectiveness of the flu vaccine in the United States. Senior Investigator Karen Wernli, PhD, has led KPWHRI’s Flu VE team since 2021. Among her team members is Erika Kiniry, MPH, who has been part of the institute’s flu-tracking efforts since they began 14 years ago.

Wernli and Kiniry recently spoke about their work for Flu VE, the crucial role Kaiser Permanente Washington members and urgent care centers play in this research, and what insights their team has gleaned from the current flu season, both nationally and regionally.

How does KPWHRI track seasonal flu activity and vaccine effectiveness?

Wernli: We have staff that go out to Kaiser Permanente Washington urgent care clinics and enroll people who have symptoms of an acute respiratory illness, including a new or worsening cough within the last 7 days.  We ask them to have a nose/throat swab at the clinic and to complete a survey — including basic questions about their age, flu vaccination status, and underlying health conditions. Then we test those swabs for influenza and COVID. We also ask people to do a follow-up survey about a week later to find out if their symptoms have resolved and whether any other household members have been sick.

We cover the largest geographic region of any of the Flu VE sites, with staff enrolling participants across 4 counties at 5 Kaiser Permanente urgent care centers — Capitol Hill, Bellevue, Tacoma, Olympia, and Silverdale. Especially during respiratory virus season, it can be very, very busy and challenging logistically. This is one of the most highly effective teams I've ever worked with at the research institute! We're able to do this research because of our strong partnership with the clinical delivery system — from infectious disease and urgent care leadership to the laboratory staff at Kaiser Permanente Washington’s Renton campus. And because of the Kaiser Permanente Washington members who volunteer to help with the research.

What are the key findings from the interim report on vaccine effectiveness?

Wernli: This is the second year that the results are being reported with other networks supported by the CDC. What's interesting about that is we're able to compare across different types of populations and different data-collection methods. The results consistently demonstrated that the flu vaccine reduces flu-related outpatient visits and hospitalizations across age groups.

One thing to remember — which people learned from COVID — is that the purpose of the vaccine isn't necessarily that you won't get sick, but that you won't get so sick that you need to seek care either with your physician or to be hospitalized.

Have there been moments over the last few months that made you think “This flu season is different”?

Wernli: We were seeing test positivity as high as 70%, which is really unusual. I've never seen it that high. In a typical season, 30% is more the norm. So, this is incredible.

We also had 2 days in February where everybody who was enrolled tested positive for influenza, which is something the team hasn’t seen in their 14 years in the Flu VE network.

Kiniry: It is quite something. We’ve never seen influenza positivity as high as we're seeing it now, even in the years before COVID. Also, anecdotally, I've heard that our staff in the clinics have been encountering people too sick to enroll in Flu VE this year. I haven’t heard this in previous seasons.

Wernli: Another thing is how low COVID prevalence is during this season — it has remained really, really low.

Kiniry: Yes, this is our first year since COVID that influenza has been higher in the Flu VE network — both regionally and nationally.

Do scientists have a working theory about why this flu season has been so intense?

Kiniry: Because we’re still in the middle of the season, it's too soon to answer that question. But we do know that vaccination rates are the lowest they've been in 5 years, and they appear to keep going down. A reduction in population immunity could also be a factor. During COVID, the spread of flu was substantially reduced. As a result, people probably haven't been exposed to influenza on an annual basis like they were before the pandemic.

Wernli: In a population like Western Washington, even if we have a higher vaccination rate than you might see in other pockets or communities in the United States, it still might not reach a threshold that keeps the community healthy enough that they don't get so sick that they need to go see their doctor. It isn’t that the vaccine isn’t effective, but that there’s still too many people not vaccinated, so more people just get sick, too sick.

What’s next for Flu VE? Anything new you’re tracking?

Wernli: For almost the past year, we've been on the edge of our seats looking to see whether we might detect any cases of avian influenza in people who are enrolled in the Flu VE network. It is something that the network could contribute to if there was more crossover of avian flu to humans. We are prepared.

Kiniry: When we send our specimens to the external research lab, they do a molecular test that checks broadly for influenza A. After that, they test specifically for the common influenza A subtypes, H3N2 and H1N1. If we have a good-quality specimen that tests broadly for influenza A and it doesn't test positive for one of those two subtypes, it's flagged as “OK, something might be up with this one. Get it sent for additional testing to see if it's possibly avian flu.”

The flu season doesn’t usually end until May. Any late-season advice?

Wernli: Get your flu vaccine!

Kiniry: With the flu positivity rate still so high, it's not too late — the season's not over.

Wernli: Also, masks work for influenza as well as they work for COVID. I take this strategy: If I know I want to take a trip in a few weeks, I'll start masking up because I don't want to get sick before I go. You can use protective measures in a way that benefits you, so you're not canceling something or having to change plans because you got sick.

Wernli and Kiniry would like to acknowledge the dedicated staff, leadership, and partners who make Flu VE’s research at Kaiser Permanente Washington possible, including their colleagues on the KPWHRI Flu VE team, the care delivery teams at the urgent care clinics, the clinic lab staff, the Renton lab staff, and the many Kaiser Permanente Washington members who take part in this important research.

By Sophie Ramsey