Vaccine advisers to the Centers for Disease Control and Prevention are meeting Thursday to weigh possible limits on the use of the Johnson & Johnson vaccine because of continued blood clot issues, mostly in young and middle-aged women, according to clinicians familiar with the agenda.

The single-dose vaccine has been linked to a rare and severe type of blood clot, which halted its use for 10 days in April as federal health officials looked more closely at six women who experienced the problem — the only known cases among more than 7 million people who received the vaccine in the United States at that time. One of the women died. The pause was lifted after an extensive safety review that determined the vaccine’s benefits outweighed the risks.

On Thursday, the Advisory Committee on Immunization Practices will be presented with new data that appears to show the rate of the clots in people who received the Johnson & Johnson shot has increased since April, although the problem is still rare. There have been about nine deaths related to the issue, according to a federal official familiar with the situation.

The FDA, in an update to its fact sheet on the vaccine this week, said the highest reporting rate of clot issues — about one case per 100,000 doses administered — has been in women 30 to 49 years old.

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A comprehensive review of the blood clot condition following vaccinations between last December and Aug. 31 found six deaths among 50 confirmed cases of the blood clot condition among recipients of the one-shot regimen. During that period, 14 million doses of the vaccine were given, according to the study published last month, which has not yet been peer-reviewed.

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The panel is “certainly going to get some updates between the [April] pause and now — how many more cases are there [now] compared to before, and are there certain populations that may be at increased risk, based on age, gender and comorbidities,” said one clinician familiar with the agenda, who, like others, spoke on the condition of anonymity because they were not authorized to discuss it publicly.

After reviewing the data, it is expected to vote on whether to update its recommendation for the vaccine’s use, according to the meeting agenda. The options include leaving the current recommendation to administer it to anyone 18 or older, “get rid of it, or only use it in certain populations,” the clinician said.

Another option, according to a federal official familiar with the situation, would be to recommend the Pfizer and Moderna vaccines over the Johnson & Johnson product, making what is known as a preferential recommendation.

Any changes in the vaccine’s use would likely apply to both the initial single shots and boosters, said a second clinician knowledgeable about Thursday’s meeting.

Such a recommendation would have to be endorsed by CDC Director Rochelle Walensky to become an official recommendation of the agency.

On Monday, the CDC sent emails to state health departments asking them to “describe the predicted impacted [sic] to your jurisdiction’s COVID-19 vaccination program if Janssen [Johnson & Johnson] were no longer recommended, or were recommended only for a subset of the population,” according to a copy of the email shared with The Washington Post.

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Regulators believe the benefits of the vaccine outweigh its risks, according to the FDA’s updated fact sheet. At its discussion in April just before lifting the pause, the CDC’s vaccine advisory panel took the same position, but there was debate about whether to add additional warnings targeted to women under 50. That was not done, although the FDA and the CDC added language to fact sheets and guidance for physicians to make women younger than 50 aware of the rare risk and the availability of other coronavirus vaccines.

Jake Sargent, a spokesman for Johnson & Johnson, said the company has updated its fact sheet to include the latest information from the FDA about the rare condition. “We are committed to understanding and communicating all known risks, including rare events of [the blood clot condition], and strongly support raising awareness of the signs and symptoms of this rare event,” he said in an email.

Since April, more studies have also shown that the two-shot Pfizer and Moderna vaccines, which use the mRNA technology, have higher effectiveness in preventing hospitalizations than the Johnson & Johnson product. However they are more difficult to use for certain groups that are less likely to return for a second shot.

By far the greatest number of vaccine doses administered in the United States have been the Pfizer and Moderna products, totaling about 468 million doses, according to the CDC. About 17 million doses of Johnson & Johnson have been given.

State health officials have said the one-shot vaccine, which doesn’t require ultracold storage like the Pfizer product, is useful for vaccinating hard-to-reach communities, including migrant workers, homeless shelters, the homebound and others with limited access to health care. In some areas, where there are incentives to be fully vaccinated, getting one dose of the Johnson & Johnson vaccine meets that definition.

Still, a recommendation to limit its use or make it less preferred is not likely to have a huge practical impact because “we have ample mRNA vaccines available to us,” the second clinician said.

In conversations with patients who have received the Johnson & Johnson product, the clinician already urges those eligible for boosters to get either the Pfizer or Moderna shots because data shows greater protection if the booster uses a different technology than the original regimen.

The federal official said that if the advisers determine the Johnson & Johnson vaccine is a “less preferential vaccine,” it would also send a signal about its use outside the United States. The vaccine is authorized for use in 90 countries, according to the World Health Organization. “That could be a problem because saying that means we are making a comment for the U.S. population, which means we should not be exporting” the vaccine, the official said.

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The Washington Post’s Dan Keating contributed to this report.