The AstraZeneca Covid-19 vaccine is “safe and effective” – and its benefits outweigh any risks, the European Medicines Agency (EMA) has concluded.

However, the European regulator said it “cannot rule out definitively” a link between “a small number of cases of rare and unusual but very serious blood clotting disorders” and the vaccine, though investigations were ongoing.

Emer Cooke, EMA executive director, said this situation was not unexpected, adding that “when you vaccinate millions of people” such reports of rare events will occur.

The EMA has concluded there is no overall increase in the risk of blood clots with the vaccine, and in fact it is likely to reduce the overall risk of clots.

Ms Cooke told a press briefing: “The committee has come to a clear scientific conclusion.

“This is a safe and effective vaccine. Its benefits in protecting people from Covid-19, with the associated risks of death and hospitalisation, outweigh the possible risks.

“The committee also concluded that the vaccine is not associated with an increase in the overall risk of thromboembolic events, or blood clots.”

It comes after it emerged five men in the UK have suffered an “extremely rare” blood clot problem after having the AstraZeneca coronavirus vaccine, though no causal link with the jab has been established.

The men, aged 19 to 59, have experienced a specific type of blood clot in the brain together with low blood platelet count. One of the five has since died.

There are no details yet on whether any of them had underlying health conditions.

The UK’s Medicines and Healthcare products Regulatory Agency (MHRA) said it was looking at the reports but stressed the events were “extremely rare” and there was a possibility they could have been caused by Covid itself.

It said the cases represented a less than one-in-a-million chance of suffering this type of clot among those who have been vaccinated, while the risk of dying from Covid aged 40 to 49 is one in 1,000.

The MHRA concluded that any link between the jab and clots is unproven and the benefits of the AstraZeneca vaccine outweigh any risks.

The type of clot – cerebral venous sinus thrombosis (CVST) – prevents blood from draining out of the brain.

It is this type of clot that led Germany to halt its rollout of the AstraZeneca vaccine, prompting other countries across Europe to follow.

Officials in Germany received six reports of CVST associated with low blood platelets – all in younger to middle-age women.

The EMA said the committee had recommended “raising awareness” of possible risks associated with the AstraZeneca vaccine and ensuring they are included in the product information for the vaccine.

Ms Cooke said: “During the investigation and review, we began to see a small number of cases of rare and unusual, but very serious, clotting disorders, and this then triggered a more focused review.

“Based on the evidence available, and after days of in-depth analysis of lab results, clinical reports, autopsy reports and further information from the clinical trials, we still cannot rule out definitively a link between these cases and the vaccine.

“What the committee has therefore recommended is to raise awareness of these possible risks, making sure that they are included in the product information.

“Drawing attention to these possible rare conditions and providing information to health care professionals and vaccinated people will help to spot and mitigate any possible side effects.”

Ms Cooke said the AstraZeneca vaccine “demonstrated at least 60% efficacy in clinical trials in preventing coronavirus disease and, in fact, the real world evidence suggests that the effectiveness could be even higher than that”.

She told a press conference: “We are very much aware that some (EU) member states have paused vaccinations, waiting for EMA’s outcome of a review.

“Given that thousands of people in the EU die every day (from Covid) – in fact over 2,500 were reported one day last week – it really was crucial for EMA to review rapidly and thoroughly all the available evidence, so we made this review our highest priority.”

She added: “The scientific conclusions adopted today provide member states with the information they need to take an informed decision regarding the use of the AstraZeneca vaccine in their vaccination campaigns.”

The EMA said the CVST cases it had seen appeared to occur in more women than men.