Flu activity gaining steam in the U.S. as vaccination rates lag

Flu activity in many parts of the United States is starting to rise more rapidly, signaling that flu season is on the horizon, the Centers for Disease Control and Prevention reported Friday.

With Americans set to travel for Thanksgiving gatherings next week, people who’ve been waiting to get a flu shot should think about acting now, Alicia Budd, the CDC’s team lead for domestic flu surveillance, told STAT.

“Really what we’re seeing is a more sharp increase in activity, week over week, and we know from experience when that happens often times we are entering into that period of even more increased activity,” Budd said. “It’s a great time for people to get vaccinated, if they’ve been holding off.”

The intergenerational mixing of families at holidays like Thanksgiving and Christmas often helps flu spread more quickly through the population. “It’s a perfect environment for influenza activity to take off,” she said.

Flu vaccine uptake so far is trailing last year’s rates by a few percentage points, Budd said. The CDC estimates at this point about 35% of adults have had a flu shot. Among children ages 6 months to 17 years, about 32.6% have been vaccinated, also down a bit from this time last year.

The dominant virus so far this year is influenza A H1N1, though there is some influenza B circulating as well. Budd said so far the circulating viruses seem to be well matched to those the flu shot targets.

The CDC’s weekly influenza report, FluView, showed that in the week ending Nov. 11, 4% of people who were tested for flu were infected with the virus. That’s an increase from the previous week’s estimate of about 2.6%.

Both figures are far below what will be seen when flu activity is at its peak, when the percentage of positive tests can be as high as 25%. But the pace at which the percent of positive tests is increasing suggests the country is heading in that direction, Budd said.

Activity is picking up fastest in the southeast, south central, and southwest parts of the country, and Puerto Rico has reported significant flu transmission as well.

Flu hospitalizations have also been on the rise, with the CDC estimating that since the beginning of October there have been about 780,000 symptomatic flu cases, 360,000 medical visits for flu, 8,000 hospitalizations, and 490 flu deaths.

This year’s flu season appears to be on track to be a more traditional flu season, Budd said, though she cautioned that influenza is so mercurial that it’s hard to predict from year to year what will happen. At the very least, though, the ultra-early season seen in 2022 isn’t on the cards for 2023.

“We’re not seeing the extremely early increases in activity like we did last year,” she said. “But I think at this point we just don’t know where it’s going to go. It still has time to do something unusual. But for right now, things do feel, timing-wise and impact-wise, more like what we saw pre-Covid.”