WASHINGTON: The US is recommending a pause in using the single-dose Johnson & Johnson Covid-19 vaccine to investigate reports of potentially dangerous blood clots.

The Centers for Disease Control and Prevention and the Food and Drug Administration said on Tuesday they were investigating unusual clots 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; there was one death and all remained under investigation.

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 US, from AstraZeneca. More than 6.8 million doses of the J&J vaccine have been given in the US, the vast majority with no or mild side effects.

Federally run mass vaccination sites will pause the use of the J&J shot, and states and other providers are expected to follow. The other two authorised vaccines, from Moderna and Pfizer, make up the vast share of Covid-19 shots administered in the US and are not affected by the pause.

I’d like to stress these events appear to be extremely rare. However Covid-19 vaccine safety is a top priority, FDA Acting Commissioner Janet Woodcock said at a news conference. We expect it to be a matter of days for this pause.

A CDC committee 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.

CDC’s Dr. Anne Schuchat said authorities have not seen similar clots after use of the Pfizer or Moderna vaccines, and that people should continue to get vaccinated with those shots.

FDA officials emphasised that Tuesday’s action was not a mandate. Doctors and patients could still use J&Js vaccine if they decide its benefits outweigh its risks for individual cases, said Dr Peter Marks. The agencies 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.

J&J said in a statement it was aware of the reports of blood clots, but that no link to its vaccine had been established. The company also said it is delaying the rollout of its vaccine in Europe as a precaution. US 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.

While it’s not clear yet if the reports among J&J recipients are related, doctors would treat these kinds of unusual clots like they treat people who have the heparin reaction with different kinds of blood thinners and sometimes an antibody infusion, said Dr Geoffrey Barnes, a clot expert at the University of Michigan.

As authorities investigate whether the clots really are related to the J&J vaccine, Barnes stressed that it’s important Americans get vaccinated as soon as possible using the other two available vaccines, from Pfizer and Moderna.

Published in Dawn, April 14th, 2021