Most Americans should be given the Pfizer or Moderna vaccines instead of the Johnson & Johnson shot that can cause rare but serious blood clots, U.S. health advisers recommended Thursday.

The strange clotting problem has caused nine confirmed deaths after J&J vaccinations—while the Pfizer and Moderna vaccines don't come with that risk and also appear to be more effective, advisers to the Centers for Disease Control and Prevention said.

It's an unusual move and the CDC's director, Dr. Rochelle Walensky, must decide whether to accept the panel's advice.

Until now the U.S. has treated all three COVID-19 vaccines available to Americans as an equal choice, since large studies found they all offered strong protection and early supplies were limited. J&J's vaccine initially was welcomed as a single-dose option that could be especially important for hard-to-reach groups like homeless people who might not get the needed second dose of the Pfizer or Moderna options.

But the CDC's advisers said Thursday that it was time to recognize a lot has changed since vaccines began rolling out a year ago. More than 200 million Americans are considered fully vaccinated, including about 16 million who got the J&J shot.

A strange clotting problem prompted the US to temporarily halt the single-dose J&J shots last April while scientists investigated. Eventually regulators decided the benefits of a one-and-done vaccine outweighed what was considered a very rare risk—as long as recipients were warned.

While it's still rare, the Food and Drug Administration told health care providers this week that more cases have occurred since the spring. They occur most in women between 30 and 49—about once for every 100,000 doses administered, the FDA said.

Overall, the government has confirmed 54 clot cases in both women and men, and nine deaths that included two men, Dr. Isaac See of the Centers for Disease Control and Prevention said Thursday. He said two additional deaths are suspected.

The CDC decides how vaccines should be used in the U.S., and its influential advisory committee is deliberating whether the newest safety data warrants any new limits on J&J's vaccine.

More than 200 million Americans are fully vaccinated, about 16 million of them with the J&J vaccine. The other two vaccines used in the U.S.—from Pfizer and Moderna—are made differently and regulators say they don't come with this clot risk. And unlike in the spring when vaccine supplies were tight, Pfizer and Moderna shots now are plentiful in the U.S.

COVID-19 itself can cause potentially deadly blood clots. But the suspect culprit for the vaccine-related kind is a rogue immune response linked to both the J&J shot and a COVID-19 vaccine made by AstraZeneca. Both of those vaccines are made similarly, using a cold virus known as an adenovirus, although AstraZeneca's shot is not used in the U.S.

The FDA this week warned that another dose of the J&J vaccine shouldn't be given to anyone who developed a clot following either a J&J or AstraZeneca shot.

At issue is a weird kind of blood clot that forms in unusual places, such as veins that drain blood from the brain, and in patients who also develop abnormally low levels of the platelets that form clots. Symptoms of the unusual clots, dubbed "thrombosis with thrombocytopenia syndrome," include severe headaches a week or two after the J&J vaccination—not right away—as well as abdominal pain and nausea.

Several other countries already have recommended age restrictions for both the AstraZeneca and J&J vaccines, or that preference be given to the Pfizer and Moderna vaccines.

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—Lauran Neergaard and Mike Stobbe