B Strain Dominating Early in the Flu Season – WebMD

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.

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