By Britain Eakin and Jeff Overley

Law360 (April 14, 2021, 10:11 PM EDT) -- A Centers for Disease Control and Prevention panel declined Wednesday to either endorse or disturb a newly issued pause on use of Johnson & Johnson's single-dose coronavirus vaccine, saying more information is needed on rare and serious possible side effects.

At the end of a four-hour emergency meeting, members of the Advisory Committee on Immunization Practices, or ACIP, elected not to issue a recommendation on the pause, instead agreeing to meet again in seven to 10 days after the CDC has gathered additional data.

The panel's punt followed debate over whether a half-dozen reports of dangerous blood clots and low platelets — among roughly 7 million recipients of J&J's vaccine in the U.S. — warranted the continuation of the pause announced Tuesday by the CDC and the U.S. Food and Drug Administration.

"Nothing in life is risk-free, but I want to be able to understand and defend the decision that I've made based on a reasonable amount of data," Dr. Beth P. Bell, a panelist and clinical professor at the University of Washington School of Public Health, said toward the end of Wednesday's meeting.

But nonvoting liaison representative Nirav Shah, director of the Maine Center for Disease Control and Prevention, said extending the pause could have dire consequences.

"Any extension of the pause will invariably result in the fact that the most vulnerable individuals in the United States, who were prime candidates for the Johnson & Johnson vaccine, will remain vulnerable," Shah said. "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."

Once the ACIP makes a recommendation, the FDA will analyze it to determine whether it should issue new guidance for administering the vaccine. The FDA had issued an emergency use authorization for the J&J vaccine in February, after an FDA advisory panel unanimously backed the vaccine for emergency use. 

The blood clot condition at issue is called cerebral venous sinus thrombosis, or CVST, and appeared in six U.S. cases along with low platelets, which ordinarily help with clotting. All six cases occurred in women ages 18 to 48 within six to 13 days of getting the vaccine, with one death reported so far.

Tom Shimabukuro, a member of the CDC's COVID-19 task force, said during the meeting that the observed condition is much rarer than typical blood clots because low platelets don't usually occur with CVST. He said that the observed cases appear to exceed the number of cases that would ordinarily be expected to show up in the general population.

Shimabukuro also said that no obvious patterns of underlying risk factors have been detected among the six U.S. cases so far.

All six instances occurred in white women, none of whom had known clotting disorders. None of the women were pregnant and only one was taking oral contraceptives, Shimabukuro said. One woman had asthma, one had high blood pressure, one had hypothyroidism and three are considered obese, he added.

The cases were initially detected through the Vaccine Adverse Event Reporting System, or VAERS, run by the FDA and CDC, which was set up to detect serious and rare vaccine side effects and flag safety issues requiring further investigation. Anyone can submit information to VAERS, including health care providers, patients or patient representatives.

Shimabukuro said the system "performed exactly as intended in this case," and said ongoing reporting to VAERS is critical to suss out the extent of the possible side effects.

Aran Maree, the chief medical officer of J&J's pharmaceutical arm Janssen Pharmaceutical Cos., said during the meeting that the benefits of the vaccine still appear to outweigh the risks.

"Based on the current data, Janssen believes the overall benefit-risk profile for our vaccine is positive across the population for which it's authorized," Maree said. "We strongly support ensuring vaccine awareness of the signs and symptoms of this very rare event, as well as the recommendations to ensure the correct diagnosis, treatment and reporting by health care professionals."

The ACIP meeting came the day after the FDA and the CDC recommended a pause in use of the J&J vaccine in the U.S. to further investigate the reported cases. The agencies said in a joint statement Tuesday that the blood clots "appear to be extremely rare."

Part of the reason for the pause is to make health care providers aware of the treatment protocol for the condition, which can't be treated with the anticoagulant drug heparin, the usual treatment for blood clots.

The CDC and FDA said anyone who develops headaches, abdominal or leg pain, or shortness of breath within three weeks of getting the J&J vaccine should contact their health care provider.

The symptoms prompting a pause in administration of the J&J vaccine in the U.S. appear similar to symptoms that European health authorities say are possibly linked to AstraZeneca's COVID-19 vaccine, which has not yet been authorized in the U.S. Some European countries suspended use of AstraZeneca's vaccine, and Denmark on Tuesday became the first to announce it would stop using the AstraZeneca vaccine altogether.

Both the J&J vaccine and the AstraZeneca vaccine use modified versions of adenoviruses, an inactive form of viruses that cause the common cold and flu-like symptoms. 

The White House said Tuesday that there are enough of the vaccines developed by Pfizer and its German partner BioNTech and the Moderna vaccine to vaccinate 300 million Americans and maintain the current pace of vaccination.

--Additional reporting by Adam Lidgett. Editing by Alanna Weissman.

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