A pause on the use of the Johnson & Johnson COVID-19 vaccine should continue until more is known about a rare vaccine side effect, a federal advisory committee decided Wednesday.
The committee will meet again in a week to 10 days to evaluate more data that is expected to become available.
Six women in recent weeks, as well as one man in an earlier clinical trial, developed a rare combination of blood clots and low platelet counts within two weeks of receiving the J&J vaccine. An eighth case with similar symptoms is under investigation.
The Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention met Wednesday to discuss the cases. It can only make recommendations and does not regulate drugs, but its advice is generally considered a gold standard by the agencies, and by other nations.
On Tuesday, the Food and Drug Administration and the CDC recommended a pause in administering the vaccine after reports of blood clots in a small number of people who received it.
The extremely rare blood clots have been reported in seven of the 7.2 million Americans who have gotten the J&J vaccine. The recent six cases were reported in women ages 18 to 48, and symptoms occurred six to 13 days after vaccination. One woman died and three remained hospitalized.
The side effect is not seen with the Moderna or Pfizer-BioNTech vaccines, which are much more widely available in the United States.
The J&J cases were reported to the CDC’s Vaccine Adverse Event Reporting System known as VAERS, which the CDC and FDA co-manage. It serves as an early warning system to monitor the safety of vaccines.
Committee members said the system worked well, quickly identifying evidence of the very rare complications within a month of the vaccine being authorized.
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One of the reasons for the pause was to alert health care professionals to the possibility of the rare blood clotting problems so they can be properly treated and reported to CDC.
There was some concern the pause might harm those most in need of the vaccine as J&J only requires one shot and is easier to store and transport than the other two authorized vaccines.
“Any extension of the pause will invariably result in the fact that the most vulnerable individuals in the United States who are prime candidates for the Janssen-Johnson & Johnson vaccine will remain vulnerable,” said Dr. Nirav Shah, director of the Maine Center for Disease Control and Prevention and director of the Association of State and Territorial Health Officials. “The most at risk will remain at risk, and those who would benefit immediately from vaccination who will remain unvaccinated for an unknown period of time.”
Committee members noted, however, that continuing the pause would not significantly affect the ability to vaccinate most Americans. The one-dose J&J vaccine so far makes up less than 5% of shots administered in the United States. The two other vaccines, by Moderna and Pfizer-BioNTech, are more widely available and have not seen such adverse events.
Roughly half of J&J vaccine recipients have not yet passed the two-week mark after their shot. That means if the side effect is more widespread, more cases may become apparent in the next two weeks.
The experts emphasized the side effect seen was specific and exceedingly rare. It involved a combination of blood clots, often in the brain, with a low platelet count. All who were tested also had an unusual antibody to platelets in their blood.
The rare condition is believed to be similar to one seen in recipients of a vaccine developed by AstraZeneca and Oxford University, which is not available in the U.S., but has been widely used in the U.K. and European Union.
That vaccine was associated with 86 cases of blood clots plus low platelet counts in the European Union, leading to 18 deaths, and 79 cases in the United Kingdom leading to 19 deaths. Most of those who developed the condition were female under age 60.
The demographics in the U.S. have been similar with the J&J vaccine. Of the recent cases, all were in adult women under age 50 who received the vaccine one to two weeks before their symptoms began.
Five of the six women first reported headaches, with the sixth reporting back pain and bruising. All six developed blood clots called cerebral venous sinus thrombosis, which prevent blood from leaving the brain. Three also developed blood clots elsewhere and four suffered brain bleeds.
A 25-year-old man who participated in the J&J clinical trial had similar symptoms of clots and low blood platelet levels, and later tested positive for the same antibody. At the time, it was not clear whether his condition was connected to vaccination.
The same antibody has been seen in at least 11 of the people who developed adverse reactions after receiving the AstraZeneca-Oxford vaccine, according to a recent scientific study.
The presence of the antibody suggests the person will react badly to the blood-thinner heparin, which at least four of the six women received before their condition was recognized. It is not clear whether the woman who died was treated with heparin, according to J&J. Tests for the antibody exist but are not widely available.
Four of the women remain hospitalized while one woman and the man recovered. Little is known so far about the eighth suspected case, a 28-year-old woman with similar symptoms.
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Members of the CDC committee said Wednesday they weren’t comfortable voting on the J&J vaccine until more can be learned about the condition and who is most likely to be affected.
It’s possible the committee could recommend limiting use of the vaccine to people over 50 or 60, who seem to be unlikely to develop the condition. Several European countries have done this with the AstraZeneca-Oxford vaccine.
But it’s not yet clear whether older people also are susceptible and just haven’t been identified because they are more likely to get blood clots.
Dr. Beth Bell, a committee member and public health expert at the University of Washington, said she couldn’t vote based on so little information, and so soon after the cases came to light.
“We’ve been looking at this issue for two days or less,” she said. “I just don’t feel we have enough information to make an evidence-based decision.”
Dr. Sandra Freyhofer, representing the American Medical Association at the meeting, said the quick but thorough government response increased her confidence in vaccine safety.
She told the group she supported the idea of continuing a pause in J&J vaccinations, “so we can figure out if this is a needle in a haystack or the tip of the iceberg.”