US authorities on Tuesday recommended an immediate pause on Johnson & Johnson (J&J) single-dose coronavirus vaccine after six recipients developed a rare disorder comprising blood clots within around two weeks of vaccination.
All six recipients of J&J's vaccine were women between the ages of 18 and 48. While one woman passed away and a second woman in Nebraska has been hospitalised in critical condition, the New York Times reported.
The company's shares also dipped 3% before the opening bell.
Meanwhile, the Centers for Disease Control and Prevention and the Food and Drug Administration, in a joint statement on Tuesday, said it was probing 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.
The country's federal distribution channels, comprising mass vaccination sites, will pause the use of the J&J shot, and states and other providers are likely to follow suit.
CDC's Advisory Committee on Immunization Practices will meet Wednesday to discuss the cases, and the FDA has also launched an investigation into them.
"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 Center for Biologics Evaluation and Research, said in a joint statement.
The move by US regulators comes less than a week after Europe's drug regulator announced that it was assessing rare blood clots in four people in the US who were administered the shot.