The European Medicines Agency, on Wednesday, said that blood clots should be listed as a "very rare" side effect of the AstraZeneca coronavirus vaccine as AstraZeneca's COVID-19 vaccine continue to outweigh the risks.

"No specific risk factors, including age, have been identified for thrombosis with the AstraZeneca shot, which could stem from an immune response," the European Medicines Agency (EMA) said in a statement.

However, the agency was asked questions about its findings as several European countries have discouraged the use of the vaccine in younger people due to the clots.

"EMA's safety committee has concluded today that unusual blood clots with low blood platelets should be listed as very rare side effects" of the AstraZeneca jab, the Amsterdam-based regulator said in a statement.

EMA chief Emer Cooke stressed that people should continue to take the vaccine as part of the battle against the disease.

"The safety committee has confirmed that the benefits of the AstraZeneca vaccine in preventing COVID-19 overall outweigh the risk of side effects," Cooke told a virtual news conference.

"It is saving lives."

European countries have reported dozens of cases of people with clots in blood vessels draining from the brain after receiving jabs, some of them fatal.

"The evidence we had did not allow us to draw any causal link between the different gender or age groups," Cooke said.

"A plausible explanation for these rare side effects is an immune response to the vaccine."

The EMA studied 86 blood clotting cases, 18 of which were fatal, out of around 25 million people in Europe and Britain who received the AstraZeneca vaccine. Most of the cases were in women aged under 60.

A British government panel said on Wednesday that most people under 30 should be offered an alternative to the AstraZeneca jab, but the EMA said it did not have the evidence to make a similar recommendation.