Flu shot season is upon us.

Pharmacies began giving out the vaccines — which are recommended for everyone ages 6 months and older — last month. The Centers for Disease Control and Prevention recommends getting a flu shot either this month or next, since flu activity typically picks up in the fall, with cases reaching their peak sometime from December to February. 

It takes around two weeks for the vaccine to become fully effective. 

“You really want to think about getting your appointment or making your plan to get vaccinated sometime around the last half of September through the end of October,” said Dr. Judith O’Donnell, chief of infectious diseases at Penn Presbyterian Medical Center in Philadelphia.

This year’s flu shots are trivalent, meaning they protect against three flu viruses: two versions of influenza A and one type of influenza B. For more than a decade, flu shots in the U.S. also protected against a fourth strain of influenza B, but that strain hasn’t circulated since March 2020, so the Food and Drug Administration’s vaccine advisory committee elected this year to exclude it.

What to know about flu shots

Although most people need one dose of the vaccine, children up to 8 who haven’t been vaccinated for flu before should get two shots at least four weeks apart. The CDC recommends that unvaccinated children get their first shot right away.

Because adults ages 65 and up have the highest risk of severe illness from flu, they should ask for certain shots that produce a stronger immune response than a standard flu vaccine. The CDC recommends three options for this age group: Fluzone High-Dose, Flublok or Fluad. The first two are high-dose vaccines, meaning they contain a greater amount of antigen, an ingredient that triggers an immune response. Fluad, meanwhile, contains an ingredient that helps boost the immune response, called an adjuvant. 

“You have to really shop around and figure out where that’s available, because it won’t be available everywhere,” said Amanda Joy, a physician assistant at MedStar Health, a health care provider in the Washington, D.C., area. She suggested calling ahead to doctor’s offices or pharmacies.

Last year, around 25,000 people died of the flu in the U.S. and 400,000 were hospitalized.

The effectiveness of flu vaccines at preventing doctor’s visits tends to vary from year to year. Scientists choose which strains to target based on what’s circulating in other parts of the world, but it’s not a guarantee that those strains will dominate in the U.S.

“In an optimal year, you get up to about 80% [effectiveness]. In a bad year, maybe 30%,” said Dr. Michelle Barron, senior medical director of infection prevention and control at UCHealth.

Australia offers a window into what the U.S. can expect, since its flu season lasts from around June to September. This year, there weren’t an outsized number of hospitalizations or deaths.

“It looks like it was a fairly typical flu season. It didn’t necessarily start early, which was our concern last year,” Barron said.

Although some people with egg allergies may be hesitant to get flu vaccines, given that most are egg-based, the shots are still safe for that group. Joy said people with lingering concerns can seek out Flucelvax, a vaccine that’s developed using mammalian cells instead. 

Covid and flu shots can be administered at the same time

Health experts expect flu and Covid to deliver a one-two punch during the fall and winter, as they have in past years. Although the summer wave of Covid cases hasn’t died down yet, experts anticipate another wave this winter, perhaps at the same time that flu cases peak.

The new Covid vaccines target the KP.2 variant, which became dominant in the U.S. at the end of April. A genetically similar strain, KP.3.1.1, has since taken over, but the latest vaccine should still offer better protection against it than previous Covid shots.

The shots are recommended for everyone 6 months and older. Children up to 4 years old should get at least one dose of the new formula, and potentially two or three if they’ve never been vaccinated before, according to the CDC.

Everyone else should get one dose. People who recently had Covid can wait to get their shot until three months after their infection, since they’re likely to have some immunity already. 

The Covid and flu shots can be safely administered at the same time, in the same arm or different ones. The CDC recommends getting both at once for convenience, though it’s unclear if this brings additional advantages. A small study published in April found that co-administering Covid and flu shots boosted the antibody response to Covid in blood samples, but experts aren’t sure if that translates to more protection.

Getting the shots at once might also slightly increase side effects, according to a CDC study, though the reactions are still generally mild.

“You may feel some aches and some chills and maybe a low-grade temperature if you get them both together, but you could also get that from each individually,” Joy said.

She added that when finding a time to get any vaccine, it’s best to hold off if you’re feeling unwell.

“You may not get the full response you want if you’re getting vaccines while you’re sick, so it’s much better to wait ‘til you’re healthy,” she said.

How much do the shots cost?

Flu shots are available at doctor’s offices, pharmacies, health clinics and through some workplaces.

CVS and Walgreens have both Covid and flu vaccines in stock, but Walmart pharmacies only offer flu shots right now. Walmart said it’s prepared to administer Covid shots as supply becomes available. 

People with insurance shouldn’t have to pay out-of-pocket for the vaccines as long as they get them from an in-network provider. Covid and flu shots are also covered for children without insurance through the government-run Vaccines for Children Program. 

Adults without insurance may be able to find free or low-cost vaccines at some federally qualified health centers or state or local health departments, but supply can be limited. Otherwise, the Covid vaccine costs around $150 to $200 — a difference from past years, when they were free regardless of insurance status. The CDC’s Bridge Access Program, which paid for Covid shots for uninsured adults, ended in August.

Flu vaccines can range from $25 to more than $100, depending on the shot.