The EU's medicines regulator has warned there is a "possible link" between the Johnson and Johnson coronavirus vaccine and rare blood clots.
The European Medicines Agency said these rare blood disorders should be considered as “very rare side effects of the vaccine", and that warning should be added to labels.
The one-shot vaccine has not yet been approved for use in the UK.
Last week, Johnson and Johnson paused its European rollout after US officials detected six very rare blood clot cases among nearly 7 million people who had been vaccinated.
European officials reviewed eight cases reported in the United States, where more than seven million people have received the jab. All of the cases occurred in people aged under 60-years-old, but the EMA said that it hadn’t been able to identify any specific risk factors.
The safety committee of the European Medicines Agency concluded that unusual blood clots with low blood platelets should be listed as a “very rare” side effect of the vaccine.
But the EMA concluded the overall benefits of the vaccine “outweigh the risks of side effects”.
They said these cases were “were very similar to the cases that occurred with the Covid-19 vaccine developed by AstraZeneca".
Johnson & Johnson advised European governments to store their doses until the EU drug regulator issued guidance on their use.
Last week, South Africa suspended use of the J&J jab in the wake of other countries pausing their rollout, including Italy, Romania, the Netherlands, Denmark and Croatia put their J&J doses into storage.
The blood clots linked to the J&J vaccine are occurring in unusual parts of the body, such as veins that drain blood from the brain.
Those patients also have abnormally low levels of blood platelets, a condition normally linked to bleeding, not clotting.
In its statement, the EMA said the cases it reviewed of unusual blood clots in people who received the J&J shot “were very similar to the cases that occurred with the COVID-19 vaccine developed by AstraZeneca.”
With the AstraZeneca vaccine, scientists in Norway and Germany have suggested that some people are experiencing an abnormal immune system response, forming antibodies that attack their own platelets.
Eleanor Riley, a professor of immunology and infectious diseases at the University of Edinburgh, said: “Suspicion is rising that these rare cases may be triggered by the adenovirus component of the AstraZeneca and J&J vaccines."
She said that while more data was needed, “it remains the case that for the vast majority of adults in Europe and the USA, the risks associated with contracting COVID-19 far, far outweigh any risk of being vaccinated.”
The EU ordered 200 million doses of the Johnson & Johnson for 2021 and EU officials had hoped the one-shot vaccine could be used both to boost the continent’s lagging vaccination rates and to protect hard-to-reach populations, like migrant workers and the homeless.
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