From the WebMD Archives

Dec. 30, 2019 -- This year’s flu season started with a twist.

Normally, it starts around October and lasts through March or April, with the A strain of influenza dominating during the early months and the B strain showing up near the end.

But for the 2019-20 flu season, the B strain made a surprise early appearance.

The B strain is less complicated than the A strain and doesn’t change, or mutate, as much, the CDC says. It’s divided into two families, Yamagata and Victoria, with the large majority of American cases being Victoria. Type B flu only affects humans and doesn’t cause pandemics, although it is seen as more dangerous to young children.

Type A has many variations, mutates all the time, and is responsible for flu pandemics. Type A can also infect animals. It’s usually passed from human to human through airborne germs, but animals can pass the illness to humans, with wild birds commonly acting as the hosts for this virus.

If you’ve got the flu, you probably won’t be able to tell which strain caused it. The symptoms may be a little milder for the B strain, but overall, they don’t differ much: a cough, sore throat, runny or stuffy nose, body aches, headache, chills, fatigue, and sometimes fever. The recommendations are the same, and the CDC says that everybody over 6 months old should get the flu vaccine, which will protect you against type A and type B. Medications, such as Tamiflu, work against both strains as well, the CDC says.

Experts don’t know why the B strain leads the way this flu season, says William Schaffner, MD, a professor of infectious diseases and preventive medicine at Vanderbilt University Medical Center in Nashville.

“This season, that whole paradigm has been turned on its head,” he says. “This year is way odd.”

But every flu season is a little different, he says. Last flu season, the United States had back-to-back surges of A strain activity, with very little B activity.

Parents of small children should be concerned because the B strain is proving more dangerous for kids. A study published by the American Academy of Pediatrics shows the B virus killed proportionately more children than the A virus from 2010 to 2016.

Through the first 3 weeks of December, three children have died from flu-related illnesses, all of which were linked to type B, the CDC reported Friday. The CDC weekly flu tracker says that of Dec. 21, 22 children aged 16 and under have died this flu season, with 16 deaths associated with the B and six with the A strain.

Six children are known to have died in Texas from the flu, state health officials say. And the Oregonian newspaper in Portland reported that two children died in Oregon and one in Washington state.

Schaffner says he doesn’t know why the B strain is affecting kids so harshly, but he suspects that children have come in contact with the A strain before and built up some protection. “They’ve had less opportunity to experience the B strain,” he says.

Schaffner offered two pieces of advice for parents:

  • It’s never too late to have a child -- or the entire family -- vaccinated. If your child hasn’t been vaccinated this year, get it done soon. The vaccine takes about 2 weeks to fully kick in, he says, and it protects against the A and B strains.
  • If there’s flu in your community and your child gets a respiratory illness, don’t hesitate to call your health care provider. They may be able to treat the problem before it turns into influenza.

Other groups that are vulnerable to the B strain of the flu are people over 65; people with other illnesses, such as heart disease or diabetes; and pregnant women.

“Any woman pregnant right now should be vaccinated,” Schaffner says. “It’s safe. Women who get flu who are pregnant are more likely to have the complications of flu.”

Another benefit is that the flu vaccine protection passes through the placenta to newborns, one of the populations most vulnerable to influenza, he says.

Show Sources “Types of Influenza Viruses.” “Flu & You.”

William Schaffner, professor of infectious diseases and preventive medicine, Vanderbilt University Medical Center, Nashville.

Pediatrics: “Influenza-Associated Pediatric Deaths in the United States, 2010-2016.” Weekly U.S. Influenza Surveillance Report. “Influenza Antiviral Medications: Summary for Clinicians.”

The Oregonian: “3 children die of flu in Oregon, Washington.”

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