"EMA has found a possible link to very rare cases of unusual blood clots with low blood platelets, [...] but it confirms that the overall risk-benefit remains positive," says the European regulator in a statement.

The EMA points out that its safety committee on human medicines has therefore decided, at today's meeting, that "a warning about unusual blood clots with low blood platelets should be added to the product information for the Janssen vaccine", and should be “listed as very rare side effects of the vaccine”.

At issue is an EMA investigation into eight rare cases of blood clots associated with low levels of blood platelets after taking the vaccine in the United States, one of which was deadly, out of a total of seven million people vaccinated.

As covid-19 "is associated with a risk of hospitalisation and death", the EMA insists that "the overall benefits of the Janssen vaccine in preventing the disease outweigh the risks of side effects".

The European regulator on the AstraZeneca vaccine against covid-19 has already had a similar understanding.

In this investigation, the EMA also found that "all cases occurred in people under 60 years of age within three weeks after vaccination, most of them women", without having been able to confirm specific risk factors, identical to what had already occurred said about the AstraZeneca vaccine.

"Health professionals and people who will receive the vaccine must be aware of the possibility of very rare cases of blood clots", the entity said, reiterating, however, the "safe and effective use of vaccines against Covid-19".

On 9 April, the EMA began an investigation into blood clotting cases in the states after taking Johnson & Johnson's covid-19 vaccine, days before the drug arrived in the European Union (EU).

As early as 13 April, US health officials recommended a pause in the administration of Janssen's anti-covid-19 vaccine, to allow investigating reports of blood clots potentially associated with taking the drug.

This situation led the company to delay sending the single-dose drug to Europe.

Last Wednesday, Portugal received the first 31,200 doses of Janssen's vaccine against covid-19, which have been stored, awaiting a decision by the European regulator.