Warning on Flu: It's Not Going Away Just Yet, CDC Says

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Flu season may have started several months ago, but it isn't going away just yet — U.S. health officials expect flu activity to remain high for at least a few more weeks, according to a new report.

The report, from the Centers for Disease Control and Prevention, said that flu activity in the U.S. started to increase around mid-December, and remained elevated as of Feb. 4, the most recent date for which flu data is available.

Specifically, the report said that from Jan. 29 to Feb. 4, the percentage of patients visiting the doctor for flu-like symptoms was 4.8 percent. That's well above the "national baseline" for flu visits — the threshold for what's typically seen in the off-season — which is 2.2 percent. [Winter Sickness: How to Tell If It's a Cold or the Flu]

And so far, the percentage of doctor's visits for the flu has exceeded the national baseline for eight consecutive weeks, the report said. During the last five flu seasons, the percentage of doctor's visits for the flu remained above the national baseline for 13 consecutive weeks, on average.

Thus, "elevated influenza activity in parts of the United States is expected for several more weeks," according to the report, which was published today (Feb. 16) in the CDC journal Morbidity and Mortality Weekly Report.

Flu activity has been moderate so far this season, the report said, though it is worse than last year, when the percentage of doctor's visits for the flu did not go above 4 percent. But it's a less severe year than the 2014 to 2015 flu season, when the percentage of doctor's visits for the flu peaked at 6.1 percent.

The predominate flu strain circulating this season is H3N2, which tends to cause more severe flu seasons, with more hospitalizations and deaths from the flu, compared with seasons when other strains predominate, according to the CDC.

So far this flu season, the hospitalization rate for the flu is 24 per 100,000 people, the report said. That's much higher than the hospitalization rate for the flu that occurred around this time last year, which was about 2 per 100,000 people. But it's lower than the hospitalization rate during the 2014 to 2015 season, which was about 36 per 100,000 people around this time of year.

Despite the moderately severe flu season, there is good news — this year's flu shot appears to be working relatively well. People who got a flu shot this year were about 50 percent less likely to visit the doctor for the flu, compared with people who weren't vaccinated, according to a separate report from the CDC. Data from previous flu seasons show that, in general, flu vaccines reduce the risk of visiting the doctor for the flu by about 50 to 60 percent.

To prevent the flu, the CDC recommends a flu shot for everyone ages 6 months and older. After vaccination, it takes a person about two weeks to build up immunity against the flu.

Original article on Live Science.

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.