The agency’s Advisory Committee on Immunization Practices voted 13-1 Tuesday to approve updated jabs from Moderna, Pfizer, and Novavax for the vast majority of U.S. residents. Shortly thereafter, the federal health agency announced that it had accepted the committee’s recommendation, and that vaccines would be available later in the week.

The U.S. Food and Drug Administration has yet to approve Novavax’s updated formula. But the agency authorized such boosters from Moderna and Pfizer on Monday.

The CDC anticipates having adequate booster supply and shouldn’t need to prioritize certain groups—like the elderly or immunocompromised—for first doses, federal health officials said at the Tuesday committee meeting.

“Vaccination remains the best protection against COVID-19 related hospitalization and death,” the CDC said in a late Tuesday news release announcing its decision. “Vaccination also reduces your chance of suffering the effects of Long COVID. If you have not received a COVID-19 vaccination in the past two months, get an updated COVID-19 vaccine to protect yourself this fall and winter.”

With the end of the federal health emergency, the U.S. government is no longer providing free COVID vaccines to everyone. Still, most Americans should be able to get a new booster for free, the agency said. Most insurance plans will cover the booster at no cost, including Medicare and Medicaid. Those who are uninsured or underinsured can get a free vaccine at local health centers or state, local, tribal, or territorial health departments. Pharmacies participating in the CDC’s Bridge Access Program will also provide free vaccines. And children eligible for the Vaccines for Children program—about 50% of kids in the U.S.—can receive a free vaccine from a participating provider.

Without insurance or other financial assistance, Moderna’s new jab will cost $129, Pfizer’s $120, and Novavax’s $130 per dose, company representatives said at Tuesday’s committee hearing.

All eligible should get the new booster when possible, Dr. Georges Benjamin, executive director of the American Public Health Association, told Fortune on Tuesday.

“It is clear that the vaccine remains safe and effective at all ages,” he said. “People at high risk will especially benefit from the vaccine.”

In a statement provided to Fortune, the American Medical Association on Tuesday said it welcomed the committee’s recommendations, contending that the updated jabs would prevent about 400,000 hospitalizations and 40,000 deaths over the next couple of years.

“We continue to strongly urge everyone to stay up to date on their COVID-19, influenza, and RSV vaccines to protect themselves and their loved ones from severe complications, hospitalization, and death,” the organization said, adding that it expected an increase in infections this fall and winter.

New boosters are dated but should still help

Last year’s updated Omicron boosters, released around Labor Day, were bivalent, tailored to both Omicron and the initial strain of COVID. This year’s boosters are monovalent, meaning they’re tailored to just one strain of the virus: XBB.1.5 “Kraken,” which dominated in the U.S. and elsewhere late last year into early this year.

The strain is now nearly extinct. XBB.1.5 was estimated to be responsible for just 3.1% of U.S. infections 10 days ago, according to the latest variant data the CDC has made available.

While the newest jabs are tailored to a dying strain of Omicron, they’re still expected to protect against severe disease and death from currently circulating strains, the vast majority of which are members of the XBB viral family.

While the official names of COVID strains can be quite confusing, high-flying variant EG.5, nicknamed “Eris,” is also an XBB-family variant, meaning updated boosters should provide good defense against it. As of 10 days ago, the variant was projected to be the most common COVID strain in the U.S., responsible for more than a fifth of cases.

The formula for the new vaccines “is highly similar to the EG.5-related variants circulating now,” Dr. Stuart Ray, vice chair of medicine for data integrity and analytics at Johns Hopkins’ Department of Medicine, told Fortune on Tuesday.

Recently released preliminary data shows that refreshed boosters should also offer decent protection against new, highly mutated Omicron spawn “Pirola” BA.2.86. It’s not a member of the XBB family, and is instead thought to have evolved from so-called “stealth Omicron” BA.2.

The updated vaccine’s protection against Pirola won’t be as good as the protection it offers against EG.5 and other XBB variants, Ray said. Still, there is more to immunity than antibodies, produced by B cells in response to infection and vaccination. The other, oft-forgotten half of the immune system, T cells, provides protection against severe disease. While T cells can’t prevent infection like B cells can, they still help soften the blow—of a BA.2.86 infection, EG.5 infection, or otherwise.

An unofficial vaccine priority list

While there will be no triaging of patients for new COVID boosters, the most vulnerable—including the elderly, those with weak immune systems, and young children who haven’t yet received a COVID vaccine—should be sure to schedule their shot ASAP, Dr. Ali Alhassani tells Fortune. He’s head of clinical services at Summer Health, a subscription-based pediatrics service accessible via text message in all 50 states, as well as an attending physician at Boston Children’s Hospital and an instructor at Harvard Medical School.

Dr. Roy Gulick, chief of the division of infectious disease at New York-Presbyterian/Weill Cornell Medicine, agreed with Alhassani, telling Fortune that those who are pregnant, as well as those with underlying disease, should also “prioritize this vaccine” along with the flu vaccine, which can be given at the same time.

While COVID-19 hospitalizations and deaths are lower than they have been in prior years, they’ve increased by 10% to 20% in recent weeks—good reason to schedule your fall shots, he added.

Dr. John Schumann—a Tulsa, Okla.-based primary care doctor and internal medicine specialist with Oak Street Health, a chain of primary care clinics that serve older adults—hopes everyone gets the new jab.

But “at the very least, seniors over the age of 65 and immunocompromised individuals should,” he told Fortune.

“As COVID variants continue to evolve, seniors are still at high risk for hospitalization or even death from COVID or complicating factors,” he said.

Dr. Carlos del Rio, president of the Infectious Disease Society of America, agreed with Schumann, saying in a statement that “the most important people to receive this new vaccine” are those at high risk, including the elderly and those with pre-existing conditions.

Those who didn’t receive last year’s Omicron booster should also make getting this year’s Omicron booster a priority, Schumann added.

“With cold weather coming, we expect more indoor gatherings to lead to a further uptick in cases this winter,” he said. “Getting boosted in October or November is a good way to either prevent yourself from catching the virus, or to reduce the severity of it if you do catch it.”

A (temporary) anecdote for waning immunity

Population immunity to COVID—from infection, vaccination, or both—wanes in roughly three to six months. If the CDC’s goal is to maintain “robust hybrid immunity” among U.S. residents, the agency should approve boosters for everyone and “strongly encourage uptake,” Ryan Gregory told Fortune on Tuesday, ahead of the agency’s decision. Gregory is a biology professor at the University of Guelph in Ontario, Canada, who is leading the charge in assigning nicknames like “Kraken” and “Eris” to high-flying variants, for ease of communication.

The agency’s decision to offer the vaccine to virtually all Americans was the initial step Gregory was hoping for. But the vaccine alone isn’t enough, he said. That’s because it “may not stop reinfections” and is only expected to prevent severe outcomes like hospitalization and death, Raj Rajnarayanan—assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., and a top COVID-variant tracker—told Fortune.

Because COVID vaccines aren’t entirely preventative, mitigation tools like masks, respirators, proper ventilation, air filtration, and social distancing are still necessary, Gregory said. A bonus: They work against all variants.

Rajnarayanan hopes that federal health officials will instruct vaccine manufacturers to continually submit data on how their latest formulations are holding up against the latest COVID variants—and “leave room for updating the vaccine, even as a bivalent formulation.”

Boosters should no longer target one particular variant, but problematic mutations appearing in many COVID variants in tandem, like the so-called “flip mutations” expected to rear their ugly heads this fall, Rajnarayanan and Gregory maintain.

If troublesome mutations arise after a new booster is released, drug-makers should focus on the fast development of tailored monoclonal antibodies—lab-made treatments given to high-risk patients via infusion that can block the virus from entering cells, thus curbing infection—according to Rajnarayanan.

Currently, monoclonals are needed for BA.2.86 and variants with “flip” mutations. If these are developed, society will have the tools it needs to combat the virus—the new booster, the antiviral Paxlovid, and adequate IV treatments—and should be set, he said.

For now, anyway.