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

In a joint statement, the Centres for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) said they were investigating clots in six women in the days after vaccination, in combination with reduced platelet counts.

More than 6.8 million doses of the J&J vaccine have been administered in the US.

US federal distribution channels, including mass vaccination sites, will pause the use of the J&J vaccine, and states and other providers are expected to follow.

The CDC’s Advisory Committee on Immunisation Practices will meet on Wednesday to discuss the cases and the FDA has also launched an investigation of the cases.

“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 Centre for Biologics Evaluation and Research, said in a joint statement.