In this April 13, 2021, file photo, a box of Johnson & Johnson vaccines are shown. (Szilard Koszticsak/MTI via AP, File)

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 officials said 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 more effective, said advisers to the Centers for Disease Control and Prevention.

The panel recommended the unusual move of giving preference to the Pfizer and Moderna vaccines, and late Thursday the CDC's director, Dr. Rochelle Walensky, accepted 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 during a meeting 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.

New data from unprecedented safety tracking of all those vaccinations persuaded the panel that while the blood clots linked to J&J's vaccine remain very rare, they're still occurring and not just in younger women as originally thought.

In a unanimous vote, the advisers decided the safer Pfizer and Moderna vaccines are preferred. But they said the shot made by J&J's Janssen division still should be available if someone really wants it — or has a severe allergy to the other options.

"I would not recommend the Janssen vaccine to my family members" but some patients may -- and should be able to -- choose that shot, said CDC adviser Dr. Beth Bell of the University of Washington.

The clotting problems first came up last spring, with the J&J shot in the U.S. and with a similar vaccine made by AstraZeneca that is used in other countries. Eventually U.S. regulators decided the benefits of J&J's one-and-done vaccine outweighed what was considered a very rare risk — as long as recipients were warned.

European regulators likewise continued to recommend AstraZeneca's two-dose vaccine although, because early reports were mostly in younger women, some countries issued age restrictions.

COVID-19 causes deadly blood clots, too. But the vaccine-linked kind is different, believed to form because of a rogue immune reaction to the J&J and AstraZeneca vaccines because of how they're made. It 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.

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

Overall, the government has confirmed 54 clot cases— 37 in women and 17 in men, and nine deaths that included two men, the CDC's Dr. Isaac See said Thursday. He said two additional deaths are suspected.

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