Just 60% of people in the U.S. are fully vaccinated against COVID, and many fear that as anti-jab rhetoric spreads across the country (often divided along political lines, with those in red counties less likely to be vaccinated), it’s also stopping individuals from receiving their flu shots. 

On top of that, only 40.9% of American adults have received a flu vaccine this year, according to the Centers for Disease Control and Prevention, a significant drop in rates from this time last year. An estimated 20.8 million flu vaccinations were administered in doctor’s offices the week of Nov. 13 of this year—in 2020 that number was 26.5 million.

Flu jabs are down all across the board. Vaccination for all children is six percentage points lower this season than it was last year, and just 11.1% of Medicare users over the age of 65 have received this year’s shot, compared with 28.5% at the same time in 2020.

The correlation between those who have eschewed both their flu shots and COVID vaccinations is extremely high, the CDC found. About 71% of adults who are vaccinated or definitely plan to get a COVID-19 vaccine have received or intend to receive a flu shot this season. Meanwhile, just 10.9% of adults who probably or definitely will not get COVID-19 vaccine have received or intend to receive a flu vaccine.

The CDC warned recently of heightened influenza activity this year. 

“An increase of influenza A(H3N2) viruses has been detected in recent weeks, with most of these infections occurring in young adults. CDC also is aware of influenza outbreaks in colleges and universities in several states,” the agency said in a statement.

The A(H3N2) virus, the dominant flu strain this year, is particularly aggressive. In previous years when it was the main strain, hospital rates and deaths among those over 65 were elevated. 

Flu season peaks from December to February each year, around the same time COVID-19 peaks, because of colder weather and holiday get-togethers. 

“We assume if one’s bad and the other’s bad, then together they’ll be worse,” said Dr. Aaron Milstone, a pediatrician and associate hospital epidemiologist with an expertise in pediatric infectious disease at Hopkins Hospital, in the Johns Hopkins newsletter.  

Last year’s flu rate was atypically low due to mask wearing and social distancing, but as restrictions loosen, trouble abounds, added Milstone. “If people didn’t get the flu vaccine last year and they didn’t get flu last year, then their immune system may not be in prime condition this year to respond,” he said. 

A serious flu season puts hospital capacity under substantial strain, and adding a surge in COVID cases could create serious shortages of resources that lead to unnecessary deaths, experts warn. 

“We’re in uncharted territory,” infectious disease specialist Soniya Gandhi, MD, and associate chief medical officer at Cedars-Sinai, said in a statement in October. “It’s possible that due to the relaxing of COVID-19 safety measures and with not enough public immunity to the flu because few people were exposed to it last year, we may be in for a more severe flu season.” Simultaneous infection of both COVID and the flu are possible, she added: “It’s never good for your body to be fighting off two potentially deadly infections at the same time.”

Experts say it is absolutely safe to receive a flu shot and COVID-19 booster vaccine at the same time.