US health agencies have called for a pause of the rollout of the Johnson & Johnson vaccine as they investigate several incidents of blood clots.

In a joint statement on Tuesday, the Centers for Disease Control and Prevention and the Food and Drug Administration said they were reviewing six reported US cases of “rare and severe” blood clots in individuals who had received the J&J vaccine. The individuals were all women aged between 18 and 48, who developed symptoms 6 to 13 days after vaccination. 

Nearly 7m doses of the J&J jab have been administered in the US. 

The CDC said it would review the cases at a meeting of its advisory committee on immunisation practices on Wednesday, while the FDA also investigates the significance of the blood clots. 

“Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution,” they said, adding that it was important for health bodies to properly understand and plan treatment for the particular type of blood clot.

J&J said it was continuing to work closely with experts and regulators to assess the data.

“We are aware that thromboembolic events including those with thrombocytopenia have been reported with Covid-19 vaccines. At present, no clear causal relationship has been established between these rare events and the Janssen Covid-19 vaccine,” it said. 

The call to suspend rollout of the J&J vaccine over blood clot fears follows similar issues with the Oxford/AstraZeneca jab.

The J&J shot is also approved in the EU, where rollout is slated to begin on Wednesday. The European Medicines Agency, which is reviewing a number of cases of blood clots in individuals who received the J&J vaccination, did not immediately respond to a request for comment. It has so far said there is no evidence of a causal link.

Additional reporting by Hannah Kuchler and Donato Paolo Mancini