US regulators have recommended a pause on the use of Johnson & Johnson's Covid vaccine over reports of a "rare and severe type of blood clot" in six out of millions vaccinated.
"Today FDA and @CDCgov issued a statement regarding the Johnson & Johnson #COVID19 vaccine. We are recommending a pause in the use of this vaccine out of an abundance of caution," US drug regulator Food and Drug Administration tweeted.
The FDA said over 6.8 million people had been administered the single dose vaccine in the US and the FDA and CDC (Centre for Disease Control) were reviewing data on six reported cases of a "rare and severe type of blood clot in individuals after receiving the vaccine. Right now, these adverse events appear to be extremely rare," it added.
The cases were being analysed and reviewed, said the FDA.
"Until that process is complete, we are recommending this pause. This is important to ensure that the health care provider community is aware of the potential for these adverse events and can plan due to the unique treatment required with this type of blood clot," said the agency.
Johnson & Johnson's vaccine is the first to be listed by the WHO as one-shot.
Studies have shown that the Johnson & Johnson vaccine is 66 per cent effective in preventing cases of moderate to severe illness and 85 per cent effective against severe cases of COVID-19. It completely prevented hospitalizations and death four weeks after inoculation, according to studies.