US federal health agencies on Tuesday recommended pausing the use of Johnson & Johnson's COVID-19 vaccine after six recipients developed a rare disorder involving blood clots, in a fresh setback to global efforts to tackle the pandemic.The move comes a week after European regulators said they had found a possible link between AstraZeneca's COVID-19 vaccine and a rare blood clotting problem that had led to a small number of deaths.Johnson & Johnson's (J&J) single dose vaccine - most COVID-19 shots are delivered over two doses - and AstraZeneca's low-cost vaccine are seen as vital tools in the fight against a pandemic that has claimed more than three million lives. An advisory committee to the US Centers for Disease Control and Prevention (CDC) will hold a meeting on Wednesday to review the cases linked to the J&J vaccine, and the US Food and Drug Administration (FDA) will review the analysis, the agencies said in a joint statement.All six recipients were women between the ages of 18 and 48, and the symptoms occurred six to 13 days after vaccination.In the cases, a type of blood clot called cerebral venous sinus thrombosis (CVST) was seen in combination with low levels of blood platelets (thrombocytopenia).The CDC and FDA said the adverse events appeared to be extremely rare. J&J said it was working closely with regulators and noted no clear causal relationship had been established between the events and the COVID-19 vaccine made by its Janssen unit.One woman died and a second in Nebraska has been hospitalized in critical condition, the New York Times reported, citing officials. (https://nyti.ms/3g70oLK)As of April 12, more than 6.8 million doses of the J&J vaccine had been administered in the United States.J&J's shares were down 3% before the opening bell.The US move comes less than a week after Europe's drugs regulator said it was reviewing rare blood clots in four people in the United States who had received the shot.European officials have said J&J began delivering its COVID-19 vaccine to EU countries on Monday and had committed to delivering 55 million doses to the bloc by the end of June and another 120 million in the third quarter.Europe's drugs regulator continues to recommend the use of AstraZeneca's COVID-19 vaccine, saying the benefits outweigh the risks. Several EU countries, however, have limited its use to certain age groups.Australia has no current plans to add J&J's coronavirus vaccine to its immunization drive, authorities said on Tuesday, as it moves away from procuring vaccines under review for potential links to blood clots.