• By Deborah Balzer

Infectious Diseases A-Z: Number of flu cases dropping; season not over

April 9, 2018

a young man sitting on a couch blowing his nose, with a cold, sinus allergies or a flu bugThe number of flu cases is dropping, but flu season is not over. The Centers for Disease Control and Prevention (CDC) says many states still are reporting flu cases, with influenza B more frequently reported than influenza A.

“The influenza season at this time has tapered off substantially," says Dr. Pritish Tosh, an infectious diseases specialist at Mayo Clinic. "This was an especially bad influenza season and looks like from many metrics – influenza-like illness, hospitalization, death – this is probably the worst influenza season we’ve had in a decade.”

Watch: Dr. Pritish Tosh discusses flu season.

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There are many reasons why this flu season has been worse than others, including the virus itself. "Epidemics caused each year by H3N2 viruses are often more severe than those caused by H1N1 viruses," says Dr. Tosh. "And this year was caused by a H3N2 virus. In general, the vaccine is least effective against H3N2 viruses, so an overall vaccine efficacy of about 60 percent but about 30 percent against H3N2."

The CDC reports 142 flu-associated pediatric deaths so far in the 2017 – 2018 season. “One thing to note is that even if people get influenza who got vaccinated, they are likely to have fewer complications," says Dr. Tosh. "The vast majority of the children who died of influenza this season were unvaccinated. We know that when you give the vaccine to older people who have underlying medical comorbidities that they are less likely to die from exacerbations of those medical comorbidities caused by influenza.”

A seasonal flu vaccine remains the best protection against the flu. “I recommend that everybody over age 6 months get the influenza vaccine every year,” says Dr. Tosh.

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