The U.S. is recommending a “pause” in administration of the single-dose Johnson & Johnson for the coronavirus disease 2019 (Covid-19) to investigate reports of potentially dangerous blood clots.
In a joint statement Tuesday, the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) said they were investigating unusual clots in six women that occurred 6 to 13 days after vaccination. The clots occurred in veins that drain blood from the brain and occurred together with low platelets. All six cases were in women between the ages of 18 and 48.
The reports appear similar to a rare, unusual type of clotting disorder that European authorities say is possibly linked to another Covid-19 vaccine not yet cleared in the U.S., from AstraZeneca.
More than 6.8 million doses of the J&J vaccine have been administered in the U.S., the vast majority with no or mild side effects.
U.S. federal distribution channels, including mass vaccination sites, will pause the use of the J&J shot, and states and other providers are expected to follow. The other two authorized vaccines, from Moderna and Pfizer, make up the vast share of Covid-19 shots administered in the U.S. and are not affected by the pause.
CDC’s Advisory Committee on Immunization Practices will meet Wednesday to discuss the cases and the FDA has also launched an investigation into the cause of the clots and low platelet counts.
“Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution,” Dr. Anne Schuchat, principal deputy director of the CDC, and Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a joint statement.
They are recommending that people who were given the J&J vaccine who are experiencing severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after receiving the shot contact their health care provider.
U.S. health authorities cautioned doctors against using a typical clot treatment, the blood-thinner heparin. “In this setting, administration of heparin may be dangerous and alternative treatments need to be given,” the FDA and CDC said.
European authorities investigating the AstraZeneca cases have concluded clots appear to be similar to a very rare abnormal immune response that sometimes strikes people treated with heparin, leading to a temporary clotting disorder.
Officials say they also want to educate vaccine providers and health professionals about the “unique treatment” required for this type of clot.
Johnson & Johnson said it was aware of the reports of “thromboembolic events,” or blood clots, but that no link to its vaccine had been established.
“We are aware that thromboembolic events including those with thrombocytopenia have been reported with Covid-19 vaccines,” said Johnson & Johnson in a statement. “At present, no clear causal relationship has been established between these rare events and the Janssen Covid-19 vaccine.”
The J&J vaccine received emergency use authorization from the FDA in late February with great fanfare, with hopes that its single-dose and relatively simple storage requirements would speed vaccinations across the country. Yet the shot only makes up a small fraction of the doses administered in the U.S. as J&J has been plagued by production delays and manufacturing errors at the Baltimore plant of a contractor.