CDC Warns of Second Wave of Flu Virus: What to Know About Influenza B

In the last few weeks, this flu season seemed like it was beginning to taper off. But the U.S. Centers for Disease Control and Prevention warns that things may get worse. Friday’s Weekly U.S. Influenza Surveillance Report shows there’s a new dominant strain of the flu that’s picking up where the previous one left off.

As Inverse previously reported, the 2017-2018 flu season has been especially severe, thanks to the dominant strain, influenza A(H3N2). This strain is particularly resistant to the vaccine, which led to the flu spreading rapidly across the country. The A strains are now subsiding, but Friday’s report suggests influenza B — which includes Victoria and Yamagata — is on the rise. Parents should take note, as doctors have observed that influenza B is especially deadly for young children. And now that the B strain is taking over, people who already got sick with the A strain could get the flu again.

“We know that illness associated with influenza B can be just as severe as illness associated with influenza A,” CDC spokesperson Kristen Nordlund told CNN. “We also know that influenza B tends to be more severe for younger children.” And since the antibodies your body may have produced in response to influenza A won’t protect you from influenza B, it’s possible to get the flu twice in a season.

As you can see on the CDC chart above, the proportion of flu cases attributed to influenza B is on the rise, so we’re not out of the woods yet. Overall, though, flu cases are declining, which is good news since the CDC announced in early February that the flu season hadn’t peaked yet. The coming weeks will show us just how severe this season’s epidemic turns out to be.

Between the flu season’s official start in October 2017 and the end of the most recent report, March 17, 2018, the number of pediatric deaths has reached 133. Surprisingly, the CDC announced in February that healthy children are at a higher risk for bacterial co-infection than those with underlying conditions.

And while the flu season is nearly over, Nordlund says this final phase is unpredictable: “We often see a wave of influenza B during seasons when influenza A H3N2 was the predominant virus earlier in the season. Unfortunately, we don’t know what the influenza B wave will look like.”