Flu Cases Surging In MI: What To Know About Subclade K Mutation

The predicted surge of influenza cases, driven by the new “subclade K” mutation, is hitting Michigan emergency rooms as holiday get-togethers put people in close spaces where the flu virus can easily spread.

Flu activity is high or very high in 48 states and jurisdictions, according to the latest data from the Centers for Disease Control and Prevention. At least 11 million people have gotten sick, and 5,000 people have died from the flu this season as vaccination rates wane. At least nine of those who died were children.

The CDC said the current influenza wave is expected to last several weeks. The agency also noted that RSV activity is elevated in many areas of the country, with emergency room visits and hospitalizations increasing in children under 4. COVID-19 activity is low but increasing nationally.

Michigan is among 19 other states with "very high" flu levels, the highest category the CDC recognizes.

As of the week ending Dec. 27, there were 2,110 flu hospitalizations across Michigan. The bulk of those cases (1,426) were from southeastern Michigan. More than half of those hospitalizations were people 65 and older, according to state data.

Only 23.9 percent of Michiganders have received the flu vaccine and 8.3 percent had received the latest COVID-19 booster so far this season, according to state data.

It’s influenza that is causing the most concern among health care providers. This year’s flu season is more serious for a few reasons. One is that the subclade K mutation emerged after the vaccine was chosen for the Northern Hemisphere, last February. Once the mutation became established, there wasn’t time to develop a better-matched vaccine. That leaves more people susceptible because the virus has found a way to evade pre-existing immunity from either an infection or vaccination.

Influenza A strain H3NS has mutated seven times, making the flu a more serious threat than in years past. It caused a severe flu season around the world, including in the U.K., Canada, Japan and Australia. Recent CDC data shows that nearly all virus samples since late September were the subclade K mutation.

“Right now we’re seeing clade K everywhere we are seeing influenza” in the U.S., Andrew Pekosz, a professor and vice chair of the department of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, said in a pre-Christmas news conference.

Even with a mismatch, health experts advise people to get flu shots, saying they should provide some protection against severe disease and death. The CDC recommends influenza vaccination for everyone 6 months and older who has not yet been immunized this flu season. Currently, approximately 130 million doses of the flu vaccine have been distributed across the U.S.

In mid-December, the CDC estimated 42 percent of Americans had gotten their flu shots. Rates vary greatly by age, with around 60 to 70 percent of older adults over age 65 getting their shots. Coverage varies from year to year, but generally falls far short of the 70 percent goal for herd immunity. Some flu seasons have seen vaccine coverage around 47 percent.

Pekosz, speaking at a Dec. 23 news conference, said the mutations “may allow it to evade some but not all of the influenza-vaccine-induced protection.”

“We’re still in the middle of trying to figure out whether it’s producing worse illness or whether what we’re seeing is a large number of cases that are increasing, and then there’s a correspondingly similar increase in terms of the severe illness,” he said.

The advice to get vaccinated was still on the CDC website on Monday, when the agency announced a major overhaul of the childhood vaccine schedule. Flu shots will be recommended in shared clinical decision-making, which means patients and providers will discuss vaccination before proceeding. This approach was adopted last year for most COVID-19 and hepatitis B vaccine recommendations.