An advisory panel to the Centers for Disease Control and Prevention declined to make any new recommendations on the use of the Johnson & Johnson Covid-19 vaccine, which will remain paused as the investigation into rare reports of severe blood clots continues.
Many of the experts on the committee said they did not have enough information at this time to make a decision, particularly while the other two Covid-19 vaccines authorized in the U.S. are widely available and have no such safety concerns.
It will be at least a week until the panel is scheduled to reconvene.
"We do need to better understand the risk, which we know is going to be very rare, very low, but we really don't know exactly how low," or how best to treat the cases, Dr. Beth Bell, a member of the advisory panel and a clinical professor in the department of global health at the University of Washington in Seattle, said during the meeting Wednesday.
Most experts agreed that the continued pause on Johnson & Johnson's use should not be indefinite, and would like to reconvene within the coming weeks to make a decision.
The Centers for Disease Control and Prevention convened the meeting Wednesday of the Advisory Committee on Immunization Practices, or ACIP. The committee is an independent panel of health experts, outside of the CDC.
Some ACIP members expressed concern over a continued pause, particularly as the number of new cases reported each day continues to hold steady at more than 60,000 per day.
"I continue to feel we're in a race against time and the variants," Dr. Grace Lee, a professor of pediatrics at Stanford University School of Medicine, said during the meeting. "But we need to do so in the safest possible way."
Given the wide availability of other Covid-19 vaccines at this time and the severity of the risk — though rare — the committee is "in a little bit of a different position, and we can be much more cautious and thoughtful," Dr. Helen Talbot, an associate professor of medicine at Vanderbilt University in Nashville, Tennessee.
Talbot said much remains unknown about other potential clotting issues, such as stroke and blood clots in the lungs. "We don't have enough data," she said. "My suspicion is that events like stroke may be underreported or not flagged," especially among people over the age of 50.
The Food and Drug Administration is paying close attention to the committee's analysis. The FDA could alter Johnson & Johnson's emergency use authorization if new findings as the investigation continues. Currently, the vaccine is authorized for emergency use in people ages 18 and older.
Rare blood clots
The CDC, along with the FDA, first recommended the pause Tuesday after six people developed rare but serious blood clots after getting the Johnson & Johnson vaccine shots. All 50 states temporarily stopped administering the shots.
The six cases involved rare blood clots in vessels leading out of the brain, called cerebral venous sinus thrombosis, or CVST, as well as low levels of platelets. All of the cases were in white women between ages 18 and 48 and occurred six to 13 days after they received the shot.
Three patients also developed clots in other parts of the body. No one was pregnant or had recently given birth. Three were obese. One person reported hormone therapy.
No other pre-existing conditions linking the cases were identified.
One person, a woman in Virginia, died. Four patients have not yet recovered. The sixth has been released from the hospital.
A seventh patient, a 59-year-old woman, developed deep vein thrombosis. That condition usually involves clots in the legs.
There was also discussion of a case of a 25-year-old man who developed CVST during the clinical trials after receiving the vaccine. Another person experienced the same blood clot, but had received the placebo during the trial, not the actual shot.
Though extremely rare, Dr. Tom Shimabukuro, a member of the CDC's Covid-19 Vaccine Task Force, said he estimated the clotting events to be at least three times higher than what would normally occur in women between the ages of 20 and 50.
During a media briefing earlier Wednesday, Walensky urged health care providers to be on alert for such problems, which require alternative treatments from usual blood clots.
"It is imperative for health care workers to know that the treatment of these clots is different than our current standard of care," which is a common blood thinner called heparin, she said.
Rarely, and independent of Covid-19, heparin can actually trigger blood clots. The formation of those clots seems to mirror what's happening in these rare cases after administration of the Johnson & Johnson vaccine.
Other intravenous blood thinners may be more appropriate while the investigation is ongoing, Walensky said.
"There may be additional cases to report," she said. "We want people who have received a vaccine, and their health care providers, to be aware of these events, and report them to the CDC and FDA."
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Symptoms include severe headaches, neurological problems, visual disturbances, abdominal pain, nausea and shortness of breath within 13 days of getting the shot. These are problems, Walensky said, that are severe enough to require a trip to an emergency department.
As of Wednesday afternoon, 7.4 million doses of the Johnson & Johnson vaccine had been administered.
Half of those were given within the past two weeks, meaning 3.7 million recipients may still be in the window where they should be watching for symptoms.
The vast majority of the 195 million Covid-19 vaccine shots given in the U.S. thus far are made by either Moderna or Pfizer-BioNTech. There have been no reports of similar blood clots with low platelets associated with those vaccines, which use a different type of technology, called messenger RNA, or mRNA.