Johnson & Johnson’s (NYSE:JNJ) COVID-19 vaccine was found to have a possible link to very rare cases of unusual blood clots with low blood platelets, the EU regulator said.

The European Medicines Agency concluded that the jab should have a warning added to the product information.

READ: Johnson & Johnson delays COVID-19 vaccine rollout in Europe as US authorities investigate blood clots

It also stated that these events should be listed as very rare side effects of the vaccine.

The Committee took into consideration all currently available evidence including eight reports from the US of serious cases of unusual blood clots associated with low levels of blood platelets, one of which had a fatal outcome.

As of 13 April, over 7mln had received the inoculation in the US.

The cases reviewed were very similar to the cases that occurred with the COVID-19 vaccine developed by AstraZeneca PLC (LON:AZN), the EMA said.

COVID-19 is associated with a risk of hospitalisation and death. The reported combination of blood clots and low blood platelets is very rare, and the overall benefits of COVID-19 Vaccine Janssen in preventing COVID-19 outweigh the risks of side effects, it added.

One plausible explanation for the combination of blood clots and low blood platelets is an immune response, leading to a condition similar to one seen sometimes in patients treated with heparin called heparin induced thrombocytopenia, HIT.

J&J’s jab was authorised in the EU last month but the company has delayed deliveries after it was suspended in the US over concerns of blood clots.