The Centers for Disease Control and Prevention issued a health advisory Wednesday that cases of influenza have been rising among young adults in recent weeks.
While flu cases are still low nationally, more than 90 percent are among children and young adults ages 5 to 24, according to the CDC.
Most cases are of the H3N2 lineage — a strain that health experts say is particularly troublesome, as it tends to mutate faster than other variants of influenza. The last time H3N2 was the dominant strain was during the 2017-18 flu season, when the U.S. had 710,000 flu-related hospitalizations and 52,000 flu-related deaths, the most since the 2009 H1N1 flu pandemic.
The CDC has been investigating a flu outbreak at the University of Michigan, where hundreds of students have tested positive. Flu outbreaks have been reported at other college campuses in the past month.
Experts are concerned that college students and other young people who may have been exposed to flu could spread it around the country as they travel home for the holidays.
“This is the time of the year when many people are going to be gathering together for the holidays for either Thanksgiving, Christmas or New Year’s, and there’s just the potential to amplify it,” said Dr. Isaac Bogoch, an infectious disease specialist at the University of Toronto.
He said people, especially those most at risk for severe disease, should get vaccinated, because the virus doesn’t stay within a particular age group for long.
“It’s coming. It’s not quite clear how large a flu season we’re going to have, but we are going to have a flu season,” he said.
Full coverage of the Covid-19 pandemic
The flu season typically runs from October to as late as May, with activity tending to peak from December to February, according to the CDC.
Influenza experts had previously said they were concerned that the country could be at risk for a severe flu season this year after seasonal flu cases reached an all-time low last year, when large parts of the country were shut down because of the coronavirus pandemic.
Experts urge people to get both Covid and flu vaccinations, saying an increase in flu infections this winter could put more burden on the country’s health care system, which is already dealing with a surge in coronavirus cases.
Download the NBC News app for full coverage of the Covid-19 pandemic
As part of the health advisory, the CDC recommended that people with flulike symptoms be tested for both influenza and Covid.
Kaitlin Sullivan contributed.
