PEMBROKE PARK, Fla. — Flu activity has ticked back up slightly in the U.S. thanks to a very small increase in infections caused by Influenza B, viruses distinct from the new Subclade K strain that’s been the biggest player this flu season so far.

“We’re actually seeing activity come back,” said Dr. Caitlin Rivers, director of the center for outbreak response innovation at the Johns Hopkins Bloomberg School of Public Health.

Rivers said the country is seeing an increase in cases of Influenza B, primarily among children aged five through 17.

“What we often see is that kids are the first to be affected by new trends, and then older age groups really start to see the effects,” said Rivers. “Flu B often becomes more common in the spring, so there’s some of that going on, but I don’t think it really explains the full rebound.”

Rivers, who also writes about infectious disease trends in her force of infection substack, says this pattern is similar to what the U.S. saw last year, when flu climbed to a second peak in late February after initially falling.

The recent winter storm across the country might also play a role.

“I am hopeful, but not certain, that the severe winter weather that a lot of the country experienced over the last week will interrupt that expansion into other age groups, but we’ll have to wait and see what happens,” said Rivers.

Influenza B strains are a whole different family of viruses.

Even if you’ve had the flu once this season, it’s possible to get it again if you catch a different strain.

The good news is this year’s flu vaccine protects against two A strains and one B strain, so the shots should offer some protection against severe illness and hospitalization.

“A majority of the deaths that we see from influenza are in older adults,” said Rivers. So extra important if you are, say, over the age of 65, that you get your flu vaccine and that you’re careful during flu season."

The CDC’s national map continues to show a high burden of influenza.

There are 29 states reporting high or very high flu activity, while 10 states are reporting moderate activity.

Eight more flu deaths in kids were reported last week, bringing the season’s total to 52.

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