There is a “possible link” between Johnson & Johnson’s Covid-19 vaccine and very rare blood clots, the European medicines regulator has said.
But the European Medicines Agency (EMA) concluded the overall benefits of the vaccine “outweigh the risks of side effects”.
The Janssen vaccine is yet to be approved for use in the UK.
The safety committee of the EMA concluded that unusual blood clots with low blood platelets should be listed as a “very rare” side effect of the vaccine.
Officials reviewed eight cases reported in the United States, where more than seven million people have received the jab.
All cases occurred in people under 60 years of age within three weeks after vaccination, with the majority seen in women.
The committee noted that the blood clots occurred mostly at “unusual sites” such as in veins in the brain, in the abdomen and in arteries, together with low levels of blood platelets and sometimes bleeding.
They said these cases were “very similar to the cases that occurred with the Covid-19 vaccine developed by AstraZeneca”.
The safety committee said that one possible explanation is an “immune response”, seen sometimes in patients treated with blood thinner medication heparin.
It said that people taking the jab and health workers should be made aware of the potential very rare side effect, adding that prompt specialist medical treatment can help aid recovery and avoid complications.
Johnson & Johnson previously confirmed it will delay rollout of its single-dose vaccine across Europe after the US paused the administration of the jab to investigate reports of potentially dangerous blood clots.
The UK has 30 million doses of the vaccine on order, but it has not yet been signed off for use by the Medicines and Healthcare products Regulatory Agency (MHRA).
The doses are expected to arrive in the second half of 2021 if approved by the regulator.
The Department of Health and Social Care (DHSC) has previously insisted Johnson & Johnson’s decision to delay the rollout of its vaccine in Europe would not derail the UK’s programme to offer a jab to all adults by the end of July.
Regulators in the UK said that they will examine “any safety reports” during their considerations on whether or not to approve the jab.