The European Union’s drug regulatory agency said Tuesday that it found a “possible link” between Johnson & Johnson’s COVID-19 vaccine and extremely rare blood clots and recommended a warning be added to the label. But experts at the agency reiterated that the vaccine’s benefits outweigh the risks.

The European Medicines Agency made its determination after examining a small number of clot cases in people vaccinated in the U.S. It said these problems should be considered “very rare side effects of the vaccine.”

J&J immediately announced it will revise its label as requested and resume vaccine shipments to the EU, Norway and Iceland. In a statement, it said: “The safety and well-being of the people who use our products is our number one priority.”

Following the EMA’s decision, EU Health and Food Safety Commissioner Stella Kyriakides tweeted that vaccinations save lives and added: “I urge Member States to follow the opinion of our experts.”

Dutch health minister Hugo de Jonge said the Netherlands would start immunizing with the J&J vaccine on Wednesday.

In March, the EMA, which oversees the use of pharmaceutical products in 27 countries across the continent with a combined population of about 448 million, likewise recommended a label change for AstraZeneca’s vaccine after finding a link between it and rare blood clots.

In both cases, the agency said the benefits of being immunized against COVID-19 outweigh the very small risks of developing the unusual clots.

“There is untold human suffering behind all of these (coronavirus) cases,” said Emer Cooke, the EMA’s executive director, noting that 3 million people worldwide have died in the outbreak. “These vaccines play an immensely important role in combating this pandemic.”

Last week, J&J halted its European rollout of the vaccine after U.S. officials recommended a pause in its use because of six cases of a very rare type of blood clot among nearly 7 million Americans vaccinated with the formula.

European officials said they considered all available evidence from the U.S., which ultimately consisted of eight cases, including one death. All occurred in people under 60, but the EMA said that it hadn’t been able to identify any specific risk factors.

The EMA’s Cooke said that no unusual blood clot cases connected to the J&J vaccine had been reported in Europe and that the agency will require further studies from the company as its vaccine is rolled out.

Last week, Johnson & Johnson advised European governments to store their doses until the EU drug regulator issued guidance on their use. Widespread use of the shot in Europe has not yet started.

The delay was a further blow to vaccination efforts in the EU, which have been plagued by supply shortages, logistical problems and the persistent concerns over clots.

Last week, South Africa suspended use of the J&J vaccine in the wake of the U.S. pause, and countries including Italy, Romania, the Netherlands, Denmark and Croatia put their doses into storage. But other countries, including Poland, France and Hungary, said they would move forward with their J&J immunization plans.

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. These 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 in recipients of the J&J shot were very similar to those seen in people who had gotten the AstraZeneca vaccine.

With the AstraZeneca vaccine, scientists in Norway and Germany have suggested that some people are experiencing an abnormal immune system response in which they form antibodies that attack their own platelets.

It’s not yet clear if there might be a similar mechanism with the Johnson & Johnson vaccine. But both the J&J and AstraZeneca vaccines, as well as a Russian one and from China, are made with the same technology.

They all train the immune system to recognize the spike protein that coats the coronavirus. To do that, they use a cold virus, called an adenovirus, to carry the spike gene into the body.

“Suspicion is rising that these rare cases may be triggered by the adenovirus component of the AstraZeneca and J&J vaccines,” said Eleanor Riley, a professor of immunology and infectious diseases at the University of Edinburgh.

The EMA said last month that the risk of rare clots associated with the AstraZeneca vaccine is lower than the blood clot risk that healthy women face from birth control pills.

The EU ordered 200 million doses of the J& vaccine for 2021. EU officials had hoped the one-shot vaccine could be used to boost the continent’s lagging vaccination rates and also protect hard-to-reach groups such as migrant workers and the homeless.

Johnson & Johnson also has a deal to supply up to 500 million doses to the U.N.-backed COVAX program, which is trying to get vaccines to billions of the world’s poor.

Any concerns about the J&J vaccine would be another unwelcome complication for COVAX. COVAX’s biggest supplier, the Serum Institute of India, announced recently it would delay shipments of the AstraZeneca vaccine for several months because of a surge of cases in India.

(AP)