The European Medicines Agency (EMA) said on Friday it has started a review to assess blood clots in people who received Johnson & Johnson’s (J&J) Covid-19 vaccine.
The EU medicine’s regulator said its safety committee "has started a review of a safety signal to assess reports of thromboembolic events" after reports of four cases, one of them fatal.
"Four serious cases of unusual blood clots with low blood platelets have been reported post-vaccination with Covid-19 Vaccine Janssen," the EMA said.
One of cases following the J&J jab happened during a clinical trial which the company responded to at the time saying there was no evidence the vaccine was at fault.
The three other cases occurred in the US, where the shot has been given to almost 5m people.
Janssen is the US pharma giant J&J's European subsidiary, which is headquartered in Belgium.
Although the European medicine’s watchdog has approved the single-shot J&J vaccine, it has not been rolled out in the bloc yet.
Ireland is due to receive the first batch of J&J vaccines around April 19, and approximately 600,000 doses are due to be delivered to the country before the end of June.