Europe's medicines watchdog said it was reviewing reports of rare blood clots in four people who received the COVID-19 vaccine developed by Janssen, the pharmaceutical arm of Johnson & Johnson.

In a statement, the European Medicines Agency (EMA) said its safety committee had started a review to assess reports of thromboembolic events, which occurred through the formation of blood clots and resulted in the obstruction of a vessel in people who received the Janssen jab, Xinhua news agency reported on 9th April. Of the four serious cases of "unusual blood clots with low blood platelets", three occurred in the United States, which had started the vaccine's rollout, while the fourth occurred during a clinical trial. One person died as a result.

The EMA said that it was not yet clear if there was a link between the vaccine and the reported conditions and that its safety committee would decide if regulatory action, such as label changes, as needed. The single-dose Janssen vaccine is currently only administered in the US under an emergency use authorization. The jab was authorized in the European Union (EU) in March, but the rollout has not started yet in any EU member state. It also said it had expanded its investigation into AstraZeneca's jab following reports of a bleeding condition.

The EMA also said on 9th April that it was probing possible links between the AstraZeneca COVID-19 vaccine and five reported cases of capillary leak syndrome in people who received the vaccine. The condition, in which blood leaks from the smallest blood vessels into muscles and body cavities, is characterized by swelling and a drop in blood pressure. Earlier this week, the EMA confirmed a possible link between AstraZeneca's vaccine and the occurrence of blood clots.