A number of European nations, including Germany, France, Italy and Sweden, have suspended use of the Oxford/AstraZeneca covid‑19 vaccine over blood clot concerns.

The World Health Organization and the European Medicines Agency (EMA) have both emphasised that there is currently no evidence linking the vaccine to blood clots and recommend that countries continue using it. Emer Cooke, director of the EMA, reiterated in an online press conference today that the agency remains firmly convinced that the benefits of the vaccine outweigh any risks.

Both organisations are performing a thorough analysis of all the available data and the EMA will be making a statement with its conclusions on Thursday 18 March.

Among 17 million people who have received the vaccine in the EU and the UK, 15 cases of deep-vein thrombosis (DVT) and 22 cases of pulmonary embolism have been reported as of 8 March, AstraZeneca said in a statement on 14 March. DVT is a blood clot in a vein, which has the potential to travel to the lungs, causing a blockage, or what is known as a pulmonary embolism.

“Many thousands of people develop blood clots annually in the EU for different reasons,” the EMA said in a statement. The number of blood clotting incidents in vaccinated people “seems not to be higher than that seen in the general population”.

In Germany, the Paul Ehrlich Institute, which advises the government on covid-19, said it had recommended the temporary suspension of the vaccine following a “noticeable increase” in cases of cerebral venous sinus thrombosis (CVST), a blood clot in a major brain vessel, soon after vaccinations.

Germany’s health minister, Jens Spahn, said at a press conference on 15 March that there had been seven reported cases that may be related to CVST out of 1.6 million vaccinations in Germany. Estimates of how many incidences of CVST you might expect in the general population over a year vary from two to five cases per million people to more than 15 cases per million, depending on the study.

“There is absolutely no data that supports [the German government’s] decision,” says César Muñoz-Fontela at the Bernhard Nocht Institute for Tropical Medicine in Germany. He says that older people and people with pre-existing health conditions, who are more at risk of blood clots generally, have been prioritised for the vaccine, which may have skewed the apparent side effects. He would like to see a comparison with a control group that has the same characteristics as the people so far vaccinated.

The International Society on Thrombosis and Haemostasis recommends that all eligible adults continue to receive their covid-19 vaccinations. “At this time, the small number of reported thrombotic events relative to the millions of administered COVID-19 vaccinations does not suggest a direct link,” it said in a statement.

“In weighing up the merits of a medical intervention, it’s really important to consider both sides of the argument: how risky is it for someone to have it versus how risky is it for them not to,” says Lucy Walker at University College London. “An increased risk of thrombosis is one of the known complications of [coronavirus] infection. The vaccines we have are incredibly good at preventing the illness caused by this virus. They will therefore prevent people from having thrombosis associated with the infection itself.”

The decision to halt use of the vaccine could have wider consequences, Walker adds. One is that it could lower vaccine uptake in general by increasing vaccine anxiety. To get the upper hand with the coronavirus, we also need to vaccinate people as quickly as possible to suppress the evolution of dangerous variants. “To have stocks of a safe, effective vaccine not being used, through an abundance of caution, potentially hinders this mission,” she says.