That’s because every season could have multiple peaks and various strains, she said. Typically, as spring approaches, there’s a shift to more cases of Influenza B, though that strain isn’t likely to be as severe as the H3N2 strain reported earlier in the season, Fricchione said. This year’s flu vaccine is also more effective against Influenza B — 42 percent versus the 25 percent against H3N2, she said, noting CDC data.