A study has been launched to assess possible links between the Johnson & Johnson company's Covid-19 vaccine and blood clots, the European Medicines Agency announced on Friday.
This announcement follows four serious cases identified, including one fatal.
The vaccine has already been authorized by the European Union.
The European Medicines Agency said on Friday it had launched a study into possible links between Johnson & Johnson's anti-Covid vaccine and blood clots after four cases were reported, including one fatal.
The EMA said its safety committee had "launched a study" intended "to assess information on thromboembolic incidents" involving people who have received the vaccine.
The European Union has authorized this vaccine but has not started using it.
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"Four severe cases of unusual clots"
"It was reported, after vaccination with the Covid-19 Janssen vaccine, four severe cases of unusual clots associated with low platelet levels," said the EMA, citing the name of the European subsidiary of the American giant.
"One case arose during a clinical trial and three arose during vaccination in the United States. One of them was fatal," added the EMA.
The European regulator has approved the Johnson & Johnson vaccine and its implementation in European Union countries is due to begin in April.
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The announcement comes as the Amsterdam-based organization has studied cases of blood clots in people who received the AstraZeneca vaccine and admitted that they were indeed side effects.
Both vaccines use an adenovirus as a vector.