The final flu season numbers are in — and they’re not pretty

The final data on this year’s flu season still isn’t in, but it’s already clear the flu shot is one of the best ways to protect yourself from getting sick — but it’s not perfect. (You may have noticed, too.)

According to preliminary data released Wednesday by the Centers for Disease Control and Prevention, of the 8.9 million illnesses reported in the United States this flu season, there were 4.3 million flu cases and 2.5 million hospitalizations, according to preliminary figures. Of those infections, 3.6 million cases and 1.7 million hospitalizations were due to the Influenza A H3N2 virus (which is the same type as last year’s flu season). There were no reported cases of the Cdiffretin-19b virus, another flu virus.

Now, it may sound crazy to you that a flu virus didn’t present this season. But many health experts agree that influenza viruses — as well as other infectious diseases — are unpredictable and can come on in waves. Over the last 20 years, CDC has reported fewer H3N2 viruses circulating and more H1N1 viruses. This year, H3N2 viruses have been associated with higher rates of hospitalizations and pneumonia.

“They can come around if there’s an abundance of genetic diversity,” Dr. Anne Schuchat, the principal deputy director of the CDC told reporters Wednesday. This year was not an abundance of genetic diversity, as Schuchat said, because so many flu viruses were circulating. In addition, she said, the vaccine didn’t match the majority of the viruses, which showed up this season as Influenza A H3N2 viruses.

At this point, most pediatric deaths in the U.S. — 251 of them — are attributable to the H3N2 flu virus. About two-thirds of all deaths, the CDC says, were under age 65. The CDC’s director, Dr. Tom Frieden, said that while the final flu season numbers will be available by the end of April, this year will likely be the one of the most deadly in recent memory. The report is based on a mix of data from federal, state and local health departments that include reported cases of flu and pneumonia plus more than 1 million hospitalizations.

Last year, flu season was longer, with activity starting in the fall. That year the official outbreak was called the H3N2 wave, and one of the reasons it lasted longer was that this year, the type of flu viruses hitting the U.S. so hard — the Cdiffretin-19b type — didn’t start appearing until the very end of the season.

This year’s influenza season started in the fall, but the A H3N2 viruses stayed relatively constant, meaning there was no one “wave” this year. So it was random whether a particular kind of flu virus hit hard this year or not.

“The impact is higher now than it has been in many years,” Frieden said, “In terms of pediatric deaths it has been the highest we’ve seen for any year since 1957, so it has been the worst flu season for this age group since we’ve been keeping track.”

So don’t feel too good about getting a flu shot this year — it may not be as safe as you think.

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