Mysteriously, flu season seems to be hitting states along America’s Pacific coast over two months early this year—based on an unusually high spike in the percentage of positive tests for influenza collected by the U.S. Centers for Disease Control and Prevention (CDC). Both the timing and the location are unusual, according to medical researchers, although an explanation appears to be emerging.
The head of the University of Washington’s Division of Infectious Disease Diagnostics, Alex Greninger, told CNN that as much as 98% of the flu samples now arriving at this lab derive from the once infamous “swine flu” strain, H1N1, albeit with a tricky new mutation. Labelled G155E, the mutation spurring this emerging flu wave seems to prevent the virus from being recognized by some preexisting human antibodies, according to Greninger, including those built up by strains used to create this year’s round of flu shots.
Greninger, a virologist, advised the public to nevertheless get their flu shots early. All signs indicate that it’s going to be a long and weird one.
“We’re basically seeing January levels of flu in the last week,” Greninger told the cable news site. “I wouldn’t be surprised to see a second flu season, like a normal flu season. You’ll have H1N1 cases that will peak in 2026, and then who knows what comes in January or February or March.”
The typical flu season in the U.S. tends to emerge first in the South before spreading westward, according to epidemiologist Caitlin Rivers, a senior scholar at the Johns Hopkins Center for Health Security. As Rivers told NPR this October, it is “uncommon to see new waves of respiratory virus start in the West,” like these past two months’ worth of flu cases, which have been migrating east from California, Washington, Hawaii, and Alaska.
Greninger said he suspects these West Coast cases are likely related to a version of H1N1 that has already hit Japan, where infections of young people managed to force closures at day-care centers and schools.
Seasonal flu can be significantly more dangerous for children in general, particularly those under the age of five, according to data from the CDC. In recent years, as many as 6,000 to 25,000 children within this age range are hospitalized annually in the U.S. over flu-related conditions.
“What people are a bit worried about is that the H1N1 strain this year hasn’t been seen by a lot of younger folk, so it may be more severe in them,” epidemiologist Jennifer Duchon, who researches pediatric infectious disease at Mount Sinai Children’s Hospital, told Reuters.
It is very much not unheard of for H1N1, a subtype of influenza A, to play a role in flu season. Each year’s seasonal flu is usually some combination of H1N1, another subtype of influenza A known as H3N2, and influenza B. What’s unusual about this year’s flu, of course, is just how overpowered this new mutant strain of H1N1 appears to be.
Of the influenza A samples CDC labs strain-tested that week, roughly 4% were H3N2, according to CDC data. And influenza B hasn’t even shown up yet at all.
Despite the growing indications that the G155E mutation apparently resists this year’s flu vaccine, however, researchers who have studied its impact have noted that some patients have been much more resilient to this strain of H1N1 than their infected peers. A team led by Jesse Bloom, a colleague of Greninger’s at the University of Washington, noted in a preprint study late last month that the reality of this “complex heterogeneity” will need to be tracked and understood quickly to better inform “pending vaccine update decisions.”
Don’t use this as an excuse not to get your flu shot this year, in other words. A second wave of the flu, potentially one led by the H3N2 strain that this year’s shot was updated to defend against, could be coming later this winter, right on schedule.
Source: Gizmodo