It’s understandable to assume the end of winter means the end of flu season, but that usually isn’t the case. According to CDC data, this flu season, while not as severe as last year’s overall, is not dropping from its peak as quickly. A pulmonologist and infectious disease specialist with whom we spoke also said this is also the time of year that flu season often starts to change in its composition, as different strains become more prominent.
“Last year’s flu season was fairly severe,” said Dr. Stephen Caminiti, the Chief of Pulmonary Critical Care at Bristol Hospital, “H3N2 was the predominant virus that was circulating.”
According to the CDC, H1N1 has been the predominant virus this season in the U.S. overall, but the proportions have been shifting over recent weeks, with a larger percentage of cases involving H3N2. Dr. Ulysses Wu, the Section Chief of Infectious Diseases at St. Francis Hospital, said such a shift isn’t uncommon.
“What will happen is that there’s a predominant flu strain that usually occurs early on, and then as that flu strain fades out, other flu strains start coming in,” he said.
“H3N2 is typically the cause of more severe influenza so the cold and flu season is not over and in Connecticut is can go into early May,” said Dr. Caminiti.
This is usually the point in the season where both H1N1 and H3N2 – both considered to be “A” strains of the influenza virus – start to fade and be replaced by the less-prevalent and less-dangerous-but-still-dangerous influenza B strains.
“Once we get into April it’s mostly Bs,” said Dr. Wu.
According to the U.S. government, the trivalent version of this year’s flu shot covers H1N1, H3N2 and a common influenza B strain. The more-common quadrivalent vaccine covers an additional “B” strain.