Johnson & Johnson will delay the rollout of its coronavirus vaccine in Europe following reports that six women in the US developed blood clots after vaccination.
It comes after US health officials recommended pausing the use of the Johnson & Johnson coronavirus vaccine out of an "abundance of caution" over the reports.
The US has administered more than 6.8 million doses of the vaccine but officials are investigating six reports of a "rare and severe type of blood clot in individuals after receiving the vaccine," the country's Food and Drug Administration (FDA), which regulates medicines, and Centres for Disease Control and Prevention (CDC) said in a joint statement.
"Right now, these adverse events appear to be extremely rare," they added in a tweet.
Six women between the ages of 18 and 48 developed blood clots, including three women who developed clots in the sinuses that drain blood from the brain.
In each of the cases, "symptoms occurred 6 to 13 days after vaccination," the FDA and CDC said.
The recommended pause in vaccination is in part to "ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot," they added.
Officials said that people who receive the vaccine who "experience severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider".
"The safety and well-being of the people who use our products is our number one priority. We are aware of an extremely rare disorder involving people with blood clots in combination with low platelets in a small number of individuals who have received our COVID-19 vaccine," Johnson & Johnson said in a statement.
"We have been reviewing these cases with European health authorities," the company added.
It comes after the European Medicines Agency (EMA) said they were reviewing reports of blood clots following vaccination with the Johnson & Johnson vaccine. At the time, they said there were four reported cases of clots, including one that was deadly.
The Johnson & Johnson jab is approved for use in the European Union but has not yet been rolled out in the bloc.
The European Commission said that it is in contact with Johnson & Johnson to follow the situation.
"The safety of our citizens is our absolute priority. We follow a science-based approach, and hence EMA's opinions," it added.
"It should be noted that as regards this vaccine, there is no data yet from the EU, as deliveries only began yesterday, and the vaccine has not yet been administered in the EU."
"The EMA, therefore, will have to rely on other regulators, from countries where the vaccine has been administered, such as the FDA, before deciding on next steps.
"The Steering Board closely follows the matter as well with a view to ensuring a coherent EU approach, which is essential in this context," it added.
The Janssen jab uses a technology similar to the AstraZeneca vaccine which had also been suspended in several European countries following reported rare but serious blood clots.
Multiple European countries have recommended that younger adults receive a different vaccine after EMA said earlier in the month that there was a "possible link" between the blood clots and the AstraZeneca jab.
The EMA emphasised that the benefits of the vaccine, which is proven to reduce hospitalisation and death, outweigh any rare risks.
The single-dose Johnson & Johnson vaccine is an essential part of the US vaccination campaign, with many states having already opened up vaccine appointments to young adults over the age of 16.