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With 19 states experiencing high levels of flu—and surely more to come—experts are seeing something they usually don’t: The flu type predominating nationally is a strain of influenza B.

That’s unusual, says Adam Lauring, M.D., Ph.D., an associate professor of infectious diseases and microbiology at the University of Michigan. Typically, a strain of flu type A is most common at this point in the year, with flu B becoming more usual during the later months of the season.

It’s no cause for alarm, Lauring says; the patterns of every flu season are always a little bit different from each other.

In fact, some people think flu B is not much to worry about. But is that true? Here, what you need to know influenza B and how to stay safe throughout flu season.

Flu Type B Can Also Make You Really Sick

The most severe flu outbreaks and pandemics (outbreaks caused by new strains) are usually the result of influenza A. But research shows that in general, the two types of flu are pretty similar.

More on flu season

A case of influenza B can cause the same level of misery—one to two weeks of fever, chills, cough, head and body aches, fatigue—as any other flu.

From the symptoms most people have, “you can’t tell them apart,” says Carlos del Rio, M.D., a professor of medicine and infectious diseases and a professor of global health at the Emory University School of Medicine in Atlanta.

And a 2014 study in the journal Clinical Infectious Diseases found that the length of a hospital stay, the intensive care unit admission rate, and the frequency of related deaths were comparable whether people were hospitalized for flu A or flu B.

Still, there are some contrasts. A particular subtype of flu A, H3N2, is linked with more severe disease than other types of flu A and B.

And some evidence suggests that influenza B might be more severe in children, Lauring says. A study published in 2016 in the journal Pediatrics found that between 2004 and 2013 in Canada, they were slightly more likely to die from a flu B infection than flu A.

Haven't Gotten the Flu Shot? Do It Now

Now that we’re well into flu season, you may think there’s little point in getting the vaccine. But the Centers for Disease Control and Prevention says that it’s not too late—and that flu vaccination is still the best way to protect yourself from this potentially serious illness, whether flu A or B are predominating. 

Getting vaccinated is especially important for people older than 65, pregnant women, and anyone who has an underlying health condition such as asthma or heart disease. These are the people who are most likely to get sick enough from the flu to need to be hospitalized.

It’s also vital for children to be vaccinated, particularly those younger than 5, who are more vulnerable to flu complications. So far, 19 children in the U.S. have died from flu this season. 

Right now, it looks like the vaccine is fairly well matched to the strains of flu circulating. But according to Lauring, it’s still too early in the season to predict whether that will remain true as the weeks progress.

You Can Catch Flu B Even If You Had Flu A

There's another reason to get the flu vaccine if you haven't done so yet: If you already had the flu once this season, you can get it again. It’s unlikely that you’ll fall prey to the same strain twice in one season, but you’re not immune to the other circulating strains.

So in addition to vaccinations, make sure that everyone in your family keeps up with good hygiene practices. That includes diligent hand-washing, and covering coughs and sneezes with an elbow or a tissue. And if you do get sick, stay home to keep from infecting others.