Don’t Celebrate the ‘End’ of Flu Season Before the Second Act

The Centers for Disease Control and Prevention may have spoken too soon when it declared the 2017–2018 influenza season to be on the wane. Now the agency says cases are mounting—though right now it’s influenza B, not the H3N2, A strain that is both more severe and less receptive to vaccines. In fact, with the week ending March 17 influenza B has usurped influenza A as the most dominant strain of the moment. It’s not uncommon for influenza B infections to rise later in the season compared with influenza A, but this strain can be quite severe for children, the CDC says. Having already had a case of influenza A does not confer protection against influenza B, so some patients may actually present with a second flu case in the same season. In any case, it’s not too late for patients to receive a vaccine if they haven’t already. As long as the virus is circulating—which it is in 17 states—patients are at risk.