A review of AstraZeneca's COVID-19 vaccine by the European Medicines Agency (EMA) has concluded that it is "safe and effective".

Use of the vaccine has been suspended here since March 14 following a recommendation by the National Immunisation Advisory Committee (NIAC). This followed reports of a small number of serious blood clotting events in adults after vaccination in some other countries.

A number of countries had halted use of the vaccine pending a review by the safety committee of the EMA. That committee has now confirmed that "the benefits of the vaccine in combating the still widespread threat of COVID-19, which itself results in clotting problems and may be fatal, continue to outweigh the risk of side-effects".

It said that the vaccine is "not associated" with an increase in the overall risk of thromboembolic events (blood clots) in those who receive it.

However, according to the EMA's executive director, Emer Cooke, during the 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 healthcare professionals and vaccinated people will help to spot and mitigate any possible side-effects," Ms Cooke commented.

The EMA said that these rare cases of blood clots are associated with thrombocytopenia, i.e. low levels of blood platelets (elements in the blood that help it to clot) with or without bleeding, including rare cases of clots in the vessels draining blood from the brain (CVST).

It emphasised the rarity of such events. Around 20 million people in the UK and European Economic Area (EEA) had received the AstraZeneca vaccine as of March 16 and the EMA had reviewed only seven cases of blood clots in multiple blood vessels (known as disseminated intravascular coagulation or DIC) and 18 cases of CVST.

The EMA pointed out that "a causal link with the vaccine is not proven", although it acknowledged that this "is possible and deserves further analysis".

However, it said that the committee's opinion is that that "the vaccine's proven efficacy in preventing hospitalisation and death from COVID-19 outweighs the extremely small likelihood of developing DIC or CVST".

Steps are already being taken to update the product information for the vaccine to include more information on these risks, the EMA added.