Explainer: Everything you need to know about the EMA's decision on AstraZeneca vaccine safety after blood clot reports

The AstraZeneca Covid-19 Coronavirus vaccine is safe to use, the EMA has reported. Photo: Reuters/Dado Ruvi

Eilish O'Regan Twitter Email

March 19 2021 02:30 AM

A decision on a safety review of the Oxford AstraZeneca vaccine has been given by the European Medicines Agency (EMA). What did they say?

The EMA’s safety committee, PRAC, concluded its preliminary review of a signal of blood clots in people vaccinated with AstraZeneca, and said the benefits in combating the still widespread threat of Covid-19, which itself results in clotting problems which may be fatal, continue to outweigh the risk of side effects. The vaccine has proven efficacy in preventing hospitalisation and death from Covid-19.

What did it say about reports of unusual blood clotting events in people who inoculated in other countries?

The vaccine is not associated with an increase in the overall risk of blood clots – thromboembolic events – in those who receive it. There is no evidence of a problem related to specific batches, or to particular manufacturing sites.

But it could not rule out a link entirely?

It said the vaccine may be associated with very rare cases of blood clots associated with thrombocytopenia, low levels of blood platelets. These are elements in the blood that help it to clot.

They may happen with or without bleeding, including rare cases of clots in the vessels draining blood from the brain (CVST).

How rare are they?

These are rare cases – around 20m people in the UK and the EU had received the vaccine as of March 16 and EMA had reviewed only seven cases of blood clots in multiple blood vessels and 18 cases of CVST. A causal link with the vaccine is not proven, but is possible and deserves further analysis.

How thorough was the investigation?

The PRAC involved experts in blood disorders and worked closely with other health authorities, including the UK’s MHRA which has experience in administering the vaccine to around 11m people. Overall the number of thromboembolic events reported – 469, with 191 from the EEA – in studies before licensing and after vaccine campaigns were rolled out was lower than expected in the general population. This allows the PRAC to confirm there is no increase in overall risk of blood clots.

Did they affect anyone in particular?

They were in younger patients and women in particular. Most occurred in people under 55 and the majority were women. Because these events are rare and Covid-19 itself often causes blood clotting disorders, the EMA said it is difficult to estimate a background rate in people who have not had the vaccine.

However, based on pre-Covid-19 figures it was calculated less than one reported case of disseminated intravascular coagulation (DIC) might have been expected by March 16 among people under 50 within 14 days of receiving the vaccine. Five had been reported. Similarly, on average 1.35 cases of CVST might have been expected among this age group whereas by the same cut-off date there had been 12. A similar imbalance was not visible in the older population given the vaccine.

Has it made any new recommendations?

A warning to be added to the vaccine information leaflet would draw attention to “possible rare conditions” to help recipients and healthcare professionals “prevent and mitigate any possible side effects”. Emer Cooke, Irish-born head of the EMA , said she would take the vaccine but she would want to be informed about what to look out for.

What will the patient safety leaflet state?

It will likely say to watch out for breathlessness; pain in the chest or stomach; swelling or coldness in an arm or leg; severe or worsening headache or blurred vision; persistent bleeding; multiple small bruises, reddish or purplish spots; or blood blisters under the skin.