By Peter Loftus 

U.S. health authorities recommended a pause in the use of Johnson & Johnson's Covid-19 vaccine in order to investigate rare but severe cases of blood clots.

The U.S. Food and Drug Administration and the U.S. Centers for Disease Control and Prevention announced the move Tuesday, after finding that six women between the ages of 18 and 48 years who got the vaccine had developed blood clots. More than 6.8 million doses have been administered in the U.S., the agencies said.

A panel of outside experts will meet Wednesday to review the matter for the CDC, while the FDA will also conduct an investigation.

The FDA said it was recommending a pause in the use of the J&J vaccine "out of an abundance of caution."

The halt comes at a dangerous time during the pandemic, as health authorities race to vaccinate as many people as possible before variants develop that can evade the shots. Among the biggest hurdles is overcoming hesitancy to get vaccinated.

The specter of blood clots could add to concerns about the safety of the shots, though vaccines from Pfizer Inc. and its partner BioNTech SE and from Moderna Inc. have proven relatively safe so far.

Pause of the J&J's vaccine use could hurt some vaccination efforts in the U.S., especially in areas that lacked the special freezers required to store the Pfizer-BioNTech and Moderna shots.

Yet the impact could be limited because Pfizer and Moderna have been ramping up production as they gained more experience making the shots and expanded their manufacturing capabilities.

The U.S. has an abundant supply of the Pfizer-BioNTech and Moderna vaccines, a Health and Human Services Department official said. The J&J vaccine won't be given at federally-run vaccination sites, the official said.

Separately, Australian health officials said Tuesday the country has decided against using J&J's shot, after a panel of scientific experts advising the government said it shouldn't buy any more vaccines of its type.

Later this month, J&J was going to begin delivering the shot to European health authorities, who had been looking forward to the new doses. Those authorities are now probing the clotting issue. J&J said last week it was aware of a small number of cases of clots after vaccination, and that there was no clear causal relationship between them and the vaccine.

J&J's vaccine was the third authorized for use in the U.S. It uses similar technology as a vaccine from AstraZeneca PLC and the University of Oxford, not yet authorized in the U.S. that has also been linked to rare cases of blood clots.

The J&J and AstraZeneca viral-vector vaccines contain a virus that causes the common cold, but which has been rendered harmless. That virus is engineered to include genetic instructions that set off an immune response to protect people against the coronavirus.

The Pfizer and Moderna vaccines use a different technology, called messenger RNA, to achieve the same goal.

J&J's vaccine is given in one dose, whereas the Pfizer and Moderna shots are given as two doses, three or four weeks apart.

In the case of J&J's shot, six women ages 18 to 48 developed blood clots after taking the J&J vaccine, the FDA and CDC said. The clots developed 6 to 13 days after vaccination. The women also had in their blood low counts of platelets, which help with clotting.

Given the nature of the side effect, doctors shouldn't use the normal course of clotting treatment, involving a drug called heparin, the FDA and CDC said. "In this setting, administration of heparin may be dangerous, and alternative treatments need to be given," they said.

The agencies said people vaccinated with J&J's vaccine should notify their doctor if they develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination.

Clots can be life-threatening, even fatal, if they choke off blood and therefore oxygen flow to the brain or heart. The type of blood clot seen in some people receiving the J&J vaccine was called a cerebral venous sinus thrombosis, which can prevent blood from draining out of the brain and can lead to a hemorrhage.

Like other Covid-19 vaccine makers, J&J, of New Brunswick, N.J., developed its shot much more quickly than it usually takes to develop a vaccine, given the urgency of the pandemic. The company began work in early 2020 and started testing the vaccine in people in July.

Certain types of blood clots were seen in a small number of subjects in the large clinical trial of J&J's vaccine that supported its authorization in late February. The FDA said there wasn't enough evidence at the time to determine whether the vaccine was causing the clots, but said it would monitor the situation.

J&J paused the large study of its vaccine in October because one vaccine recipient had a type of blood clot called a transverse sinus thrombosis resulting in a brain hemorrhage, according to an FDA document. J&J investigated and found that it wasn't related to the vaccine, and resumed the study.

J&J also has had problems manufacturing its vaccine. A batch of the vaccine's main ingredient that was being made at a contractor's plant in Baltimore was recently ruined by contamination, and no doses were distributed from the batch. Health regulators still haven't authorized the plant where the mishap occurred, hurting J&J's ability to churn out more doses.

Mass vaccination clinics administering the J&J vaccine in North Carolina, Colorado and Georgia have closed temporarily in recent weeks after some people receiving the shot experienced adverse effects. It wasn't immediately clear whether the vaccine caused them.

Earlier this month, U.K. health authorities recommended against giving AstraZeneca's shot to people under 30 years after receiving reports of rare but deadly blood clots. Countries including Canada and Germany have also restricted use.

The link between the vaccine and the clotting incidents is still unclear. Scientists in Germany and Norway said the vaccine may cause an autoimmune reaction that leads to clots in the brain.

Write to Peter Loftus at peter.loftus@wsj.com

 

(END) Dow Jones Newswires

April 13, 2021 09:37 ET (13:37 GMT)

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