(CNN) — Flu season may be getting under way, the US Centers for Disease Control and Prevention says.

While influenza activity is very low in the United States, it’s getting started and there’s enough to indicate that there will be at least some kind of flu season this year, unlike last year, when an emphasis on frequent handwashing, mask use, closures of schools and businesses, and social distancing pretty much shut down transmission of the virus.

It’s always impossible to predict what a flu season will look like, but Lynnette Brammer, lead of the CDC’s Domestic Influenza Surveillance team, said reports of more flu cases have caught her team’s attention and have her thinking flu season may have returned after its one-year break.

“Overall flu activity is still really low. It’s starting to creep up just a little bit,” Brammer told CNN.

“That gives us the idea that flu season may be starting.”

The CDC estimates that, depending on the season, flu kills anywhere from 12,000 to 61,000 people a year in the United States. During the first week of November, 14% of deaths were attributable to influenza, pneumonia or Covid-19. Only 0.3% of specimens tested came back positive for influenza this past week, the CDC found, and just 295 people have been hospitalized for flu.

On Monday, the CDC confirmed it was helping state and local health officials in Michigan investigate an outbreak of more than 500 cases among students at the University of Michigan. That’s the biggest single outbreak so far.

Brammer said what influenza cases there are seem to be among younger people ages 5 to 24.

“A lot of times, flu can happen first in younger age groups and then spread to the very young and the older age groups. It doesn’t always happen that way,” she said. “Every flu season is different.”

Influenza is complicated because several different types and strains circulate. Right now, Brammer said, a strain known as H3N2, which has been around for decades, is what’s infecting people. Flu vaccines also protect against a strain known as H1N1, which appeared and caused a mild pandemic in 2009, as well as two influenza B strains.

The CDC recommends that just about everybody six months and older should get a flu vaccine every year. That’s because the virus mutates and the formulation often gets tweaked, but also because people’s immunity wanes from year to year, even with vaccination.

Brammer said vaccine manufacturers are projecting they’ll make 200 million doses of flu vaccine this year — the biggest supply ever. That’s not enough to cover the whole US population, but historically, only about half the people who should get vaccinated against flu actually do so.

“It was best to get vaccine in October. but a lot of people just didn’t get around to it,” Brammer said. “If you haven’t been vaccinated yet, you better get around to it now.”

Many Americans are also being advised to get booster doses of Covid-19 vaccines and it’s safe and convenient to get them together, Brammer said. “This is the perfect time to go and get vaccinated if you haven’t already done it,” she said.

The CDC is worried because flu vaccination appears to have fallen behind schedule.

Flu vaccination rates for children are 6 percentage points lower this year than last year, with 34% of children having received their flu vaccine so far, compared to 40% this time a year ago. It’s 10 points lower for Black children — 24.9% compared to 35.3% last year.

Pregnant women, who are strongly advised to get flu shots both to protect themselves and their babies, are also falling behind. Only 41% of pregnant women are vaccinated so far, compared to 58% this time last year, the CDC says. And just 21.5% of Black pregnant women are vaccinated.

The CDC says, however, that overall more people say they plan to get vaccinated against influenza this year than last year. It says 58.5% of people surveyed say they plan to get a flu shot, compared to 54.8% who got one last year.

The CDC found that 70.6% of adults who are vaccinated against coronavirus or definitely plan to get a Covid-19 vaccine have received or intend to receive a flu vaccine for the 2021-22 season.

And just 11% of adults who say they probably or definitely will not get a coronavirus vaccine say they’ll get a flu vaccine.

So far, the CDC says, 162.5 million doses of flu vaccine have been distributed. Vaccine manufacturers are continuing to make and distribute flu vaccine.

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