As a result, the current pause is likely to continue until the panel can gather more evidence about the risk of rare blood clots and the possibility that the shot is responsible.
During an emergency meeting, members of the CDC’s Advisory Committee on Immunization Practices said they did not feel comfortable making a decision about whether to continue vaccinations because there was not enough evidence about the patients who experienced the serious but rare side effects.
Panel members said they wanted more information about the people who may be most at risk for blood clots such as age and gender.
The panel did not set a date for when they will meet again, but it could be in the next week to 10 days. There is also a regularly scheduled meeting on May 5.
Federal health officials recommended the pause on Tuesday to allow the CDC and the Food and Drug Administration to review six cases of a rare and severe blood clot in the brain reported among the 7 million people who received the shot.
What makes the cases so rare is that the blood clots, known as cerebral venous sinus thrombosis (CVST), were accompanied by a condition known as thrombocytopenia, where the body has a low level of platelets, which help promote clotting.
During the meeting, CDC officials and Johnson & Johnson representatives described the cases as all occurring in women between the ages of 18 and 48. Three women also had large, dangerous clots in other parts of their body as well as in the brain.
They developed symptoms, most often headaches, six to 13 days after vaccination. But the symptoms were not necessarily indicative of a serious problem, and the CDC wants clinicians to be aware of the issue, especially because the traditional treatment for clotting — the blood thinner heparin — could actually make this specific condition worse.
Panel members stressed that they did not think the shot was necessarily dangerous or that the risks outweighed the benefits. But they wanted to be cautious and continue the pause until they felt comfortable with the level of evidence.
The committee’s recommendations are non-binding, but health officials have indicated they will use the panel to help inform their final decision about the shot.
Top Biden administration officials said this week they expect the pause will last days or weeks, not months. But it’s not clear what affect the lack of a vote from the committee will have on that timeline, nor is it clear what level of evidence the committee members want before making any recommendations.
While most of the committee members who spoke seemed to favor the pause and were convinced it would only reinforce confidence in the vaccine, some expressed frustration at the lack of action, as well as about the impact a continued pause will have on vulnerable communities.
“We are in a situation where not making a decision is tantamount to making a decision,” said Nirav Shah, president of the Association of State and Territorial Health Officials and director of Maine’s public health agency.
“The most at risk will remain at risk, and those who would benefit immediately from vaccination will remain unvaccinated for an unknown period of time,” Shah added.
He urged the committee to understand the equity concerns that could arise from delaying use of the vaccine any further.
Still, other members of the committee noted that the U.S. has two alternative vaccines in the Moderna and Pfizer-BioNTech products that can be used as a backstop. Those shots use mRNA technology, while Johnson & Johnson’s and the separate AstraZeneca vaccine are based on adenoviruses.
While J&J is only a small part of the U.S. vaccination campaign, making up less than 5 percent of the doses administered so far, the administration has been counting on an influx of supply in the coming months, and Johnson & Johnson is meant to play a major role in the U.S. vaccination strategy.
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Aran Maree, chief medical officer for Janssen, the J&J division that developed the vaccine, said two people who received the shot during its clinical trials developed blood clots, including one 25-year old male who exhibited symptoms similar to the women.
Maree said the company believes the overall benefit of the vaccine outweighs the risk, but doctors should be aware of the clotting concern and be prepared to treat it appropriately.
Updated at 6:46 p.m.