Doctors have a message for vaccine-weary Americans: Don’t skip your flu shot this fall -- and seniors, ask for a special extra-strength kind.

After flu hit historically low levels during the COVID-19 pandemic, it may be poised for a comeback. The main clue: A nasty flu season just ended in Australia.

While there’s no way to predict if the U.S. will be as hard-hit, “last year we were going into flu season not knowing if flu was around or not. This year we know flu is back,” said influenza specialist Richard Webby of St. Jude Children’s Research Hospital in Memphis.

Annual flu shots are recommended starting with 6-month-old babies. Flu is most dangerous for people 65 and older, young children, pregnant women and people with certain health problems including heart and lung diseases.

Here’s what to know:

As people get older, their immune system doesn’t respond as strongly to standard flu vaccination. This year, people 65 or older are urged to get a special kind for extra protection.

There are three choices. Fluzone High-Dose and Flublok each contain higher doses of the main anti-flu ingredient. The other option is Fluad Adjuvanted, which has a regular dosage but contains a special ingredient that helps boost people’s immune response.

Seniors can ask what kind their doctor carries. But most flu vaccinations are given in pharmacies and some drugstore websites, such as CVS, automatically direct people to locations offering senior doses if their birth date shows they qualify.

Webby advised making sure older relatives and friends know about the senior shots, in case they’re not told when they seek vaccination.

“They should at least ask, ‘Do you have the shots that are better for me?’” Webby said. “The bottom line is they do work better” for this age group.

If a location is out of senior-targeted doses, it’s better to get a standard flu shot than to skip vaccination, according to the Centers for Disease Control and Prevention.

All flu vaccines in the U.S. -- including types for people younger than 65 -- are “quadrivalent,” meaning they guard against four different flu strains. Younger people have choices, too, including shots for those with egg allergies and a nasal spray version called FluMist.

Australia just experienced its worst flu season in five years and what happens in Southern Hemisphere winters often foreshadows what Northern countries can expect, said Dr. Andrew Pekosz of the Johns Hopkins Bloomberg School of Public Health.

And people have largely abandoned masking and distancing precautions that earlier in the pandemic also helped prevent the spread of other respiratory bugs like the flu.

“This poses a risk especially to young children who may not have had much if any previous exposure to influenza viruses prior to this season,” Pekosz added.

“This year we will have a true influenza season like we saw before the pandemic,” said Dr. Jason Newland, a pediatric infectious disease specialist at Washington University in St. Louis.

He said children’s hospitals already are seeing an unusual early spike in other respiratory infections including RSV, or respiratory syncytial virus, and worries flu likewise will strike earlier than usual - like it did in Australia.

The CDC advises a flu vaccine by the end of October but says they can be given any time during flu season. It takes about two weeks for protection to set in.

The U.S. expects 173 million to 183 million doses this year. And yes, you can get a flu shot and an updated COVID-19 booster at the same time - one in each arm to lessen soreness.

The companies that make the two most widely used COVID-19 vaccines now are testing flu shots made with the same technology. One reason: When influenza mutates, the recipes of so-called mRNA vaccines could be updated more quickly than today’s flu shots, most of which are made by growing influenza virus in chicken eggs.

Pfizer and its partner BioNTech are recruiting 25,000 healthy U.S. adults to receive either its experimental influenza shot or a regular kind, to see how effective the new approach proves this flu season.

Rival Moderna tested its version in about 6,000 people in Australia, Argentina and other countries during the Southern Hemisphere’s flu season and is awaiting results.