US halts J&J COVID-19 vaccine after six women under 50 develop rare blood clots

US federal health agencies recommended pausing the use of Johnson & Johnson’s COVID-19 vaccine after six women under 50 given the shot developed rare blood clots, dealing a fresh setback to efforts to tackle the pandemic.

All six cases involved women between the ages of 18 and 48, and the symptoms occurred six to 13 days after vaccination.

Following the news, Johnson & Johnson (J&J) said it was delaying the rollout of the vaccine to Europe, a week after regulators there said they were reviewing rare blood clots in four recipients of the shot in the US.

The moves come after European regulators said earlier this month they had found a possible link between AstraZeneca’s COVID-19 vaccine and a similar rare blood clotting problem that led to a small number of deaths.

The US Food and Drug Administration (FDA) said one person had died from the rare blood clotting condition after taking the J&J vaccine and another was in critical condition.

FDA acting commissioner Janet Woodcock said it expected the pause to be a matter of days, and it was aimed at providing information to healthcare providers so that they can diagnose, treat and report such blood clots.

FDA official Peter Marks said that part of the reason for the pause was to warn doctors that administering the standard treatments for clots can cause tremendous harm, or be fatal.

Most of the available J&J vaccine has been used in the United States due to production issues that have limited the company’s supply. As of April 12, more than 6.8 million doses of the J&J vaccine had been administered in the United States, compared with more than 180 million shots combined of the Moderna and Pfizer/BioNTech shots.

US health officials said during a press briefing there had been no similar blood clot cases reported among recipients of the Pfizer/BioNTech of Moderna vaccines.

An advisory committee to the US Centers for Disease Control and Prevention (CDC) will meet on Wednesday to review the cases, and the FDA will review the analysis, the agencies said in a joint statement.

J&J said it was working closely with regulators and noted no clear causal relationship had been established between the cases and the COVID-19 vaccine made by its Janssen unit.

The J&J and AstraZeneca vaccines both use an adenovirus vector – a harmless cold virus that instructs human cells to produce a protein found on the surface of the coronavirus, thereby spurring the immune system to prepare an arsenal against the COVID-19-causing virus.