An uptick in influenza B at the end of an already turbulent flu season has some worried about a second wave of the disease.

According to the Centers for Disease Control and Prevention’s weekly snapshot of flu activity in the United States, influenza strain B is now resulting in a larger number of flu cases than the A strain, H3N2, that dominated over the rest of the season.

However, while it may be disconcerting to see a different strain causing more cases of flu, rates on the whole are on the wane. Strain B rearing its head at the end of a season is actually nothing out of the ordinary, explains Dr. William Schaffner, an infectious disease expert at Vanderbilt University.

“The dominant strains every year are one of the A strains. They create the big epidemics. They create all the hullabaloo,” he said. “Now, behind the scenes as it were there are influenza B strains that are circulating at the same time. They cause illness that is just as severe, but the B strains, for biological reasons that we don’t understand, don’t create big epidemics, but they smolder along.”

A representative for the CDC also confirmed to Healthline that an increased number of influenza B-related flu cases is “not surprising” at this time of year.

Influenza B and the end of flu season

In general, flu cases have dropped dramatically in recent weeks, but B does still represent a risk. Because strain B is never as widespread as A, it sometimes has a reputation as a weaker form of the disease — but that isn’t true.

Influenza strain B can be just as severe.

It’s also possible to get sick from influenza B even if you’ve already been hit with an A strain.

But neither Schaffner nor the CDC representative believe there’s anything to indicate that the influenza B activity is more than a regular part of the flu cycle.

“I do not think that we’re going to get another upsurge in cases, certainly not a substantial number,” said Schaffner.

“Look at the other seasons, once that downward curve starts, whether slowly or quickly, they all gradually go to the baseline and you don’t see another surge up,” he said.

Still, it’s easy to understand why there might be a worry about flu striking again late in the season. After all, this year’s flu season was the worst in U.S. history since the 2009–2010 H1N1 “swine flu” epidemic.

Fortunately, influenza B can be treated both through the flu vaccine as well as antivirals, including Oseltamivir, known commonly as Tamiflu.

How to protect yourself at the end of flu season

This year’s flu vaccine struggled. It had a dismal 25 percent effectiveness rate against H3N2, the predominant strain of the season. However, it actually showed significantly better results, 42 percent, against influenza B (Yamagata lineage), the strain currently seeing a resurgence.

Schaffner said there’s a rush toward quadrivalent recombinant flu vaccines by drug developers to help cover a wider variety of flu strains.

The standard influenza vaccine currently only protects against three different strains of flu: two A and one B.

A quadrivalent, as its name suggests, protects against four strains: two A and two B.

“The reason we put a number of different virus types into the vaccine is that we are trying to cover the bases. If one doesn’t work as well, the others have a chance of preventing flu as well,” said Schaffner.

He calls this taking a “shotgun” approach to influenza virus.

Healthline reported earlier this year that Tamiflu and other antivirals are also effective against influenza B. Unlike the flu vaccine, antiviral treatments are administered after an individual has already become sick.

Other antiviral options include peramivir (Rapivab) and zanamivir (Relenza).

Even if an antiviral doesn’t defeat the flu outright, it will likely make it less severe.

As the flu season winds down, the CDC continues to recommend these actions to prevent getting sick:

  • Get vaccinated.
  • Take everyday precautions including frequent hand washing.
  • Stay away from sick individuals.
  • Take antiviral medications if they are prescribed.

“We’re at the end of the season now, and getting vaccinated now is akin to locking up the barn after the horses have been stolen,” said Schaffner.” But, fall will come, September, October, and November will arrive. That’s the time to absolutely get vaccinated. Don’t put it off.”