Flu season in America is underway with a new variant called subclade K, recent Centers for Disease Control and Prevention (CDC) data shows.
In the week ending December 6, the first full week after Thanksgiving, there was an increase in confirmed flu cases—from 348 the week before to 547, according to the CDC.
H3N2 subclade K, which was identified by the CDC in August, accounted for 89 percent of the 163 flu samples studied since September 28.
This is not ringing any alarm bells for infectious disease doctor Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, who told Newsweek, “cases are not above expected levels and the season is just beginning in earnest.”
But he went on to add that while the “season seems usual…there is anticipation that it may be at least moderate in intensity.”
Thomas A. Russo, an infectious disease doctor at Buffalo VA Medical Center, said he believes subclade K will “result in an increased spread.”
Newsweek has contacted the CDC, via email, for comment.
Why It Matters
Subclade K, a mutated influenza variant, has dominated outbreaks in Japan, the United Kingdom and Canada.
There are worries that the strain is resistant to current flu vaccines, according to the CDC, sparking concern that this flu season could be more severe.
What To Know
Among the total 547 confirmed flu cases in the week ending December 6—the majority (96 percent) were classified as influenza A, which includes the H3N2 subtype and its subclade K.
At least five public health jurisdictions were showing high or very high activity that week, the same as the week before, while at least nine recorded moderate activity, up from two.
“The timing of this increasing activity is similar to several past seasons,” the CDC says, but it went on to warn that subclade K may impact flu vaccine effectiveness.
“When circulating influenza viruses are drifted from viruses represented in the influenza vaccines, vaccine effectiveness may be reduced,” it said.
The CDC still encouraged people to get their flu jabs, saying it “continues to provide benefits” such as “protection against severe influenza illness, hospitalization, and death,” “protection against other circulating influenza viruses represented in the influenza vaccines” and “help to reduce the overall community spread of influenza.”
Dr. Russo told Newsweek that “subclass K has seven new mutations that will make prior immunity imperfect and will result in increased spread.”
“That combined with waning immunity and decreased vaccination will unfortunately likely result in another bad flu season,” he said. “Stated alternatively, a greater proportion of the population will be susceptible, which will translate into more cases, which in turn will result in more bad outcomes.”
What People Are Saying
Dr. Amesh Adalja told Newsweek: “In the U. S.—vs. Canada, Japan and the UK—cases are not above expected levels and the season is just beginning in earnest currently. Only a few states are reporting high activity of influenza and hospitals are not really seeing any pressure on capacity.
“Personally, I have only seen a few cases of influenza in the hospital. Thus far, the season seems usual but there is anticipation that it may be at least moderate in intensity given the vaccine mismatch due to the K variant.”
Dr. Thomas Russo told Newsweek: “The vaccine is not an optimal match this season, but early data suggest it will still significantly decrease the likelihood of developing severe disease resulting in hospitalization and death. It is not too late to get vaccinated.”
What Happens Next
As the U.S. flu season progresses, the CDC will continue surveillance of circulating strains and update guidance as needed. Scientists are monitoring vaccine effectiveness and watching for potential shifts in severity, particularly as more data becomes available following the holiday travel period.
The CDC continues to advise Americans to receive the annual flu shot.
