The European Medicines Agency (EMA) has concluded its safety review of the AstraZeneca vaccine, saying it ‘likely reduces’ the risk of blood clots overall.

However, the medicines regulator said it will continue to monitor events of thrombosis.

Thirteen European countries had suspended use of the Oxford/AstraZeneca vaccine whilst the review was ongoing, amid reports that some patients had suffered blood clots after vaccination.

The EMA announced in a press briefing this afternoon that there is ‘clear’ scientific evidence that the AstraZeneca vaccine is ‘safe and effective’, upon completing its review.

EMA executive director Emer Cooke said that while they could not ‘definitively’ rule out a link between vaccination and the very rare events, its recommendation is for vaccination to continue while ‘raising awareness’ of potential side effects.

She said: ‘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 thrombo-embolic events or blood clots.’

Dr Sabine Straus, chair of the EMA’s Pharmacovigilance and Risk Assessment Committee (PRAC), added that the vaccine could reduce the risk of such events thanks to its efficacy in preventing coronavirus.

She said: ‘PRAC noted that the number of thrombo-embolic events reported after vaccination is lower than expected in the general population and PRAC has concluded that there is no increase in the overall risk of blood clots with this vaccine. 

‘Moreover, because the vaccine is effective in preventing Covid-19 disease, which in itself is a cause of blood clots, it likely reduces the risks of thrombotic events overall.’

However, the EMA said that there ‘remain some concerns’ in younger patients.

Dr Straus told journalists at the briefing: ‘The PRAC review of the cases of thrombosis combined with thrombocytopenia has shown a predominance in some groups and notably in women of younger age. 

‘However, at the moment, it’s still rather premature to conclude on a very specific group because the background risk of thrombosis may be different but it may also be the case that more people have been vaccinated in this specific group.’

An EMA statement added that the vaccine ‘may be associated with very rare cases of blood clots associated with thrombocytopenia’ – low levels of blood platelets ‘with or without bleeding’, including ‘rare cases of clots in the vessels draining blood from the brain (CVST)’.

It said: ‘Cases of thrombosis and thrombocytopenia, some presenting as mesenteric vein or cerebral vein/cerebral venous sinus thrombosis, have been reported in persons who had recently received Covid-19 Vaccine AstraZeneca, mostly occurring within 14 days after vaccination. 

‘The majority of reports involved women under 55, although some of this may reflect greater exposure of such individuals due to targeting of particular populations for vaccine campaigns in different member states.’

The PRAC will undertake an ‘additional review’ of the risks, including with other types of Covid vaccines, with further studies launched and ‘close’ monitoring of reports of blood clotting disorders to continue, it added. 

It comes as UK Prime Minister Boris Johnson has said he will receive the Oxford/AstraZeneca vaccine tomorrow.

Speaking at today’s Number 10 press briefing, he said: ‘The Oxford jab is safe and the Pfizer jab is safe. The thing that isn’t safe is catching Covid, which is why it is so important that we all get out jabs as soon as our turn comes. 

‘As it happens, I’m getting mine tomorrow, and the centre where I’m getting jabbed is currently using the Oxford/AstraZeneca vaccine for those receiving their first dose, and that is the one I will be having.’

Meanwhile, the EMA has said that the vaccine’s summary of product characteristics and package leaflet will be updated with information on cases of disseminated intravascular coagulation (DIC) and CVST.

It recommended that healthcare professionals should ‘be alert for possible cases of thromboembolism, DIC or CVST’ in those vaccinated.

And patients should be warned to seek ‘immediate medical attention’ for symptoms, including ‘persistent or severe headache particularly beyond three days after vaccination’, it added.

It comes as the UK medicines regulator has said that patients with a headache lasting more than four days after their Covid vaccination should ‘seek medical attention’ in a bid to rule out thrombosis.

This is a ‘precautionary measure’ following a review of vaccine safety data which it has been undertaking in cooperation with the EMA this week.

Last week, the MHRA urged patients to continue to turn up for their AstraZeneca Covid vaccination amid ‘unconfirmed’ blood clot reports.

However, pharmacists leading vaccination sites told the Pharmacist that some patients had already been put off by the news of the European suspensions of its usage and were turning down the jab or not turning up at all.

A version of this story first appeared in our sister title, Pulse.