U.S. regulators approved updated COVID-19 shots Wednesday but limited their use for many Americans – and removed one of the two vaccines available for young children.

The new shots from Pfizer, Moderna and Novavax are approved for all seniors. But the Food and Drug Administration narrowed their use for younger adults and children to those with at least one high-risk health condition, such as asthma or obesity. That presents new barriers to access for millions of Americans who’d have to prove their risk — and millions more who may want to get vaccinated and suddenly no longer qualify.

Additionally, Pfizer’s vaccine will no longer be available for any child underage 5, after the FDA said it was revoking the shot’s emergency authorization for that age group.

Parents will still be able to seek out shots from rival drugmaker Moderna, the other maker of mRNA vaccines, which has full FDA approval for children as young as 6 months. But the company’s Spikevax vaccine is only approved for children with at least one serious health problem.

The revamped vaccines target a newer version of the continuously evolving virus and are set to begin shipping immediately. But it could be days or weeks before many Americans know if they’ll be able to get one, with access dependent on various decisions by federal health advisers, private health insurers, pharmacies and state authorities.

The new restrictions – previewed by FDA officials in May – are a break from the previous U.S. policy, which recommended an annual COVID-19 shot for all Americans 6 months and up.

The approach reflects heightened skepticism about the ongoing risks of COVID-19 and the need for yearly booster shots from Health Secretary Robert F. Kennedy Jr. and FDA Commissioner Marty Makary, who were both outspoken critics of wide-scale vaccinations.

“The American people demanded science, safety, and common sense. This framework delivers all three,” Kennedy wrote on social media.

Kenned said Novavax’s shot is only open to people 12 or older, not younger children – and under the same risk-based restrictions as are now in place for the Moderna and Pfizer options. It’s the nation’s only protein-based COVID-19 vaccine.

Some medical groups, including the American Academy of Pediatrics, have objected to the new limits, saying they may block vaccine access for families who want to protect their children. Last week, the group offered its own recommendations for kids, saying annual COVID shots are strongly recommended for children ages 6 months to 2 years and advised for older children.

That differs from the latest guidance under Kennedy, which doesn’t recommend the shots for healthy children of any age, but says kids may get the shots in consultation with physicians.

Many countries have scaled back COVID-19 vaccinations in recent years, and some U.S. experts say the change makes sense here, given that nearly all Americans have some protection from previous vaccination or infection.

But implementing the shift presents a number of logistical problems.

Insurers typically base their vaccine coverage decisions on the recommendations of a panel of advisers to Centers for Disease Control and Prevention, but some say they will also look to medical professional groups, including the American Medical Association.

Earlier this year, Kennedy dissolved the CDC panel and replaced its members with a number of doctors and researchers who have repeatedly questioned the safety of commonly used vaccines and ingredients. The panel is expected to meet in September, but no specific date has been set and no agenda released.

Depending on the panel’s advice, Americans underage 65 could be expected to provide documentation of a serious medical condition before they can get a shot. Complicating the rollout is the fact that pharmacists – who administer most COVID vaccines in the U.S. – typically aren’t expected to collect that kind of information. And laws governing their ability to administer routine vaccinations vary by state, where pharmacists are licensed.

Nearly half states limit vaccinations by pharmacists to those recommended by the CDC panel.

Access could also be complicated for healthy adults and children who are interested in getting a shot for extra protection.

If the latest vaccines aren’t covered by their insurance, those patients could be required to pay $150 or more out of pocket if they want one. They might also have to find a doctor or other health professional willing to give the shot “off label,” or outside the use listed on the FDA label. Pharmacists may be reluctant to give vaccines off-label.

The updated shots from Pfizer, Moderna and Novavax target a coronavirus subtype named LP. 8.1, a recently dominant version of the virus that is closely related to some newly emerging cousins.

All three shots were initially made available under the FDA’s emergency use authorization, an expedited process to quickly review vaccines and other countermeasures during the pandemic.

Moderna received full FDA approval in July for children down to 6 months and says it should have enough supply to meet U.S. demand.

In addition to revoking emergency use of Pfizer’s vaccine, the FDA also pulled authorization for several other therapies from the pandemic years, including convalescent plasma, which was used to treat hospitalized COVID-19 patients before the first antiviral drugs became available.

COVID-19 vaccines do a good job preventing severe disease, hospitalization and death, which remain a bigger risk for seniors and people with underlying health factors, including heart disease, lung disease and cancer.

Preliminary data from the CDC estimates 47,500 Americans died from COVID-related causes last year. In at least two-thirds of those cases, COVID-19 was listed as the underlying cause of death. For the rest, COVID-19 was a contributing factor.

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AP Medical Writer Lauran Neergaard contributed to this story.