Flu trends in King County appear to have peaked for now, but epidemiologists say our already unusual viral season means the next few months could still be unpredictable.
The region’s respiratory infection season hit harder and earlier than usual this fall, but recent county data provides some evidence that flu is subsiding in King County — or at least round one of it. During the first week of January, epidemiologists counted about 183 flu-positive tests, compared to more than 2,000 in late November.
While it’s too early to solidify statewide trends, the Department of Health’s weekly influenza surveillance update reports flu-like activity is much lower in Washington than it was in December, though deaths have increased.
The downward trend is encouraging, said Dr. Eric Chow, King County’s chief of communicable disease epidemiology. Still, he added residents should remember a few factors when looking at recent data.
“In general, we’re in a much better place than where we were earlier in the season,” Chow said. “From a public health standpoint and knowing the certain types of limitations that these types of surveillance purport, we interpret these with caution, particularly for the last couple weeks.”
For example, fewer new flu samples may have been collected over the holidays, as people opted to spend time with family or travel instead of visiting health clinics and getting tested, Chow said. In addition, clinics might be closed. Weather could be a factor.
Still, drops in other areas of flu surveillance are a “huge relief,” he said.
Although the number of collected tests dropped, the proportion of positive tests also fell. As of last week, about 6% of lab tests from area hospitals and clinics had returned positive for influenza, compared to a peak of about 40% in late November, according to county data.
There have also been recent declines in flu-related emergency-department visits and hospitalizations, though levels are still much higher now than they were at this point in past seasons.
Local trends largely reflect what the rest of the United States is tracking, too, Chow said, though the end of flu season could still be a ways off.
Because different strains of influenza often circulate throughout the course of a season, one type might have the ability to surge weeks after another, Chow said. During the 2018-19 season, for example, flu cases dipped nationwide in early January, but reemerged for a second, much stronger surge in March.
And this year has become especially epidemiologically interesting and unpredictable because, along with many other reasons, one strain of influenza B (the Yamagata lineage) appears to have vanished from the world, Chow said.
“We’ve never really witnessed something like this,” he said. “This is very new and very interesting to epidemiologists.”
Because the past few months of viral spread have been unusual in many ways, Chow said, it’s important not to pronounce the end of flu season too early.
“Otherwise people will have this false notion that their risk of influenza is low,” he said. “And, the other thing that’s important to note, just because you see a decrease in the trends … the number of infections remains really high [compared to this point in past seasons].”
Several weeks of downtrends are usually required before epidemiologists call the season, he said, adding that the next month will provide a clearer picture of how viruses spread during our holiday season.
Where are we with COVID?
COVID cases have been on the rise in King County since Christmas, jumping over 25% in two weeks, though hospitalizations are much lower than they were in mid-December.
But emerging variants, particularly the omicron XBB.1.5 subvariant, are still a concern, Chow said. XBB.1.5, nicknamed the “kraken” variant, emerged in New York several months ago, hitting the East Coast harder than in Washington, though it is circulating here and is expected to soon become the dominant strain in the region, UW Medicine virologist Dr. Alex Greninger said in a statement earlier this month.
“We’ve had a large respiratory virus season with RSV and influenza, and now it looks like it’s going to be sort of a COVID wave of infections in January” because of the XBB.1.5 subvariant, Greninger said.
XBB.1.5 has mainly sparked concern among epidemiologists because of its transmissibility, Chow said.
“Early studies had suggested that when the number of infections of XBB.1.5 increase, there seems to be a corresponding increase in hospitalizations, but we’re still waiting on additional data to make that definitive connection,” he said.
Early evidence has also shown some monoclonal antibodies, including Evusheld, are less effective against the new subvariant — though COVID vaccinations, including bivalent boosters, and other antivirals, like Paxlovid and remdesivir, are still effective, Greninger said.
Many of Public Health — Seattle & King County’s COVID vaccine clinics have closed, but Auburn’s Outlet Collection mall still takes appointments and drop-ins Fridays through Mondays from 10:30 a.m. to 7 p.m.
While the worst of fall’s flu surge has passed, Chow still recommends masking indoors, especially in crowded, indoor spaces, for the time being.
“Indoor masking, and masking in general, is still really critical because we still have high numbers of respiratory viruses,” he said. “We have to remind people that we started off really, really high [in flu levels], so even though we’re coming down, the numbers of infections are still likely to be high.”
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