As health experts implore people to be vaccinated against covid-19, they’re also reminding everyone to get an annual flu shot.

Flu shots — which are safe to get in conjunction with covid-19 vaccines or boosters — could help keep flu cases low this year, health experts said, though some worry influenza will surge after a historically mild flu season last year.

Flu shots are recommended for everyone six months or older — and the prime time to get them is within the next several weeks, said Dr. Mark Itskowitz, an internal medicine physician with Allegheny Health Network.

“The optimal time to get the flu vaccine is September or October, and that’s because influenza normally arrives in our part of the world starting in November,” he said, explaining immunity from the vaccine is conferred two weeks after getting the shot.

Flu season doesn’t peak until the winter months, though, so getting a flu shot in November or December still is better than not getting one at all, Itskowitz said.

Adults — particularly older adults whose immune systems aren’t as robust as younger people’s — should aim to be vaccinated in October or early November because their protection will wane over time, said Dr. Richard Zimmerman, a professor of family medicine and public health at the University of Pittsburgh. Younger patients, he said, can get the shots sooner because they’ll maintain immunity longer.

For those looking to be inoculated against covid-19 and the flu, Itskowitz said it’s safe to do both in the same timeframe. Some vaccines that contain live virus — such as the shingles vaccine — shouldn’t be taken too close to the covid-19 vaccine. But, because the flu vaccine contains killed or inactive virus, it’s safe to receive it at the same time as a covid-19 vaccine or booster, he said.

“We don’t anticipate any interaction, so patients should be able to get their booster for covid-19 along with their flu shot,” he said. “For the flu vaccine, we do encourage people to get it around the time a lot of people will be getting their boosters.”

It’s also safe to get the flu vaccine immediately after recovering from covid-19, he said.

All flu shots available this year are called quadrivalent vaccines, according to the Centers for Disease Control and Prevention.

“When you get a quadrivalent vaccine, versus a trivalent or bivalent, you’re covering four influenza strains,” said Dr. Carol Fox, Excela Health’s chief medical officer. “This one covers two Influenza A strains and two Influenza B strains.”

She emphasized the vaccine is safe and effective.

The efficacy of the flu vaccine varies year by year, Itskowitz said, and it’s too soon to say exactly how effective this year’s flu shot will be. People who are vaccinated against the flu, however, tend to have milder illness if they do contract influenza than those who weren’t inoculated, he said.

Last year’s flu season — the mildest in Pennsylvania’s history — was well-controlled, in part, because of historically high vaccination rates.

Last year, the CDC reported 193.8 million doses of flu vaccine had been distributed nationwide — surpassing the 174.5 million flu shots in the 2019-20 season. Many health experts last year pushed for high flu vaccination rates as a way to avoid a surge of influenza cases as covid-19 threatened to overwhelm hospitals.

Itskowitz said he’s hopeful high vaccination rates will persist and possibly bring about another mild flu season.

“My sense is that the uptake on flu vaccines will be at historic highs like it was last year, just because of the general concern about respiratory viruses in the setting of this pandemic,” Itskowitz said. “I think people are more aware than ever of the spread of viruses.”

Last year’s flu season was virtually “nonexistent,” health officials said. Allegheny County last year reported zero flu-related deaths, three hospitalizations and 180 cases — a notable drop from the previous year’s 12 deaths, 115 hospitalizations and more than 10,000 cases. Pennsylvania had a 95% decrease in cumulative case counts at the end of last year’s flu season, per the Department of Health.

Making predictions about influenza is “often challenging,” Itskowitz said. But, based on how the southern hemisphere handled influenza during their flu season in recent months, Itskowitz said some health officials “would again anticipate a lower-than-average number of cases.”

That’s particularly probable if vaccine uptake remains high and people remain vigilant, he said.

“There’s no question that any respiratory virus — including the flu — will be lessened by the use of good hand hygiene and being careful about being around people who are sick,” he said.

But other health officials worry this year’s flu season could be worse than usual. Zimmerman, who is involved with modeling studies at Pitt’s School of Public Health, said some models indicate there could be more flu this year because people weren’t exposed and gaining immunity last year.

“Our prediction is that if less social distancing and lockdowns occur like last year, as people are acting freer and kids are going to school, then we will see a compensatory surge in flu cases this year,” Zimmerman said, adding a significant jump in vaccine uptake could slow potential flu outbreaks.

The Pennsylvania Department of Health is anticipating the flu virus to circulate along with covid-19 and other common respiratory viruses that weren’t as prevalent last season, spokeswoman Amber Liggett said.

“Reduced population immunity due to lack of flu virus activity since March 2020 could result in an early and possibly severe flu season,” she said, adding “initiatives are in the works” to encourage flu vaccinations.

A mild flu season last year kept concerns of a “twindemic” — the term used to describe potential surges in covid-19 and influenza simultaneously — from becoming a reality. It could still be a potential problem this year as the highly contagious delta variant has fueled new outbreaks of covid-19 and some health experts anticipate a more severe flu season, Zimmerman said.

“If social distancing measures, lockdowns and school closures are less than last year, then we may see more flu transmission,” Zimmerman said. “If we were to have a wave of delta or a similar aggressive variant at the same time flu occurred, that could strain resources.”

Hospitals should be better prepared this year, as supply chain issues that left personal protective equipment and other necessities in short supply at the start of the pandemic have since been resolved, Fox said. She said she anticipates a “slightly more significant influenza season” is approaching but said she’s “comfortable” with their supply of personal protective equipment, ventilators and other supplies if there’s an uptick in covid-19 and influenza patients in the coming months.