U.S. federal health agencies on Tuesday called for a pause in the use of Johnson & Johnson's COVID-19 vaccine after six recipients reported blood clotting.

In a joint statement on Tuesday, the U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA) said they were reviewing data involving the six reported cases of a rare and severe type of blood clot in individuals after receiving the vaccine.

In these cases, a type of blood clot called cerebral venous sinus thrombosis was seen in combination with low levels of blood platelets.

All six cases occurred among women between the ages of 18 and 48, and symptoms occurred six to 13 days after vaccination. These adverse events "appear to be extremely rare," the statement said.

Global reactions

Canada said on Tuesday it was talking to Johnson & Johnson about reports that its COVID-19 vaccine might cause rare blood clots, with Prime Minister Justin Trudeau saying a surge in dangerous virus variants could threaten progress made so far.

The Dutch health minister on Tuesday said he did not yet know whether the Netherlands will commence its roll-out of Johnson & Johnson's COVID-19 vaccine this week as planned after the U.S. authorities paused using the vaccine.

The European Medicines Agency (EMA) said in a statement that it is not clear there is a link between the vaccine and the incidents, and its safety committee is continuing a review announced last week.

Meanwhile, South Africa has suspended the roll-out of Johnson & Johnson's COVID-19 vaccine, its health minister said on Tuesday.

"We have determined to voluntarily suspend our roll-out until the causal relationship between the development of clots and the Johnson & Johnson vaccine is sufficiently interrogated," the African country's Health Minister Zweli Mkhize told reporters, saying there had been no reports of such clots in South Africa after roughly 290,000 vaccinations.

Other countries may suffer from U.S. suspension of Johnson & Johnson

It is learned that Johnson & Johnson's COVID-19 vaccine will remain paused for a longer while after U.S. health advisers told the government on Wednesday that they need more evidence to decide if a handful of unusual blood clots were linked to the shot – and if so, how big the potential risk really is.

At an emergency meeting, advisers to the U.S. CDC expressed that the U.S. has enough vaccine choices to do without the Johnson & Johnson vaccine while other countries which are still waiting for the one-and-done shot may not.

So far, the Johnson & Johnson vaccine has been a minor player in U.S. vaccinations. More than 122 million Americans have received at least one vaccine dose, the vast majority have been inoculated with shots made by Moderna or Pfizer, and nearly 23 percent are fully vaccinated.

(With input from Reuters)