The UK has received 30 reports of the rare blood clotting events that some scientists have linked to the Oxford/AstraZeneca Covid-19 vaccine and have caused precautionary restrictions to be placed on its use in many European countries.
On Thursday, the Medicines and Healthcare products Regulatory Agency released information on 25 cases of severe and very rare blood clotting events, on top of five it had already reported this month.
The MHRA also clarified that it had not seen any of the same reactions in individuals that had received the BioNTech/Pfizer vaccine.
Concern has been growing about possible links between the AstraZeneca jab and a very specific and rare type of blood clotting event. The news that a growing number of such cases have been identified in the UK is likely to call into question the view that the phenomenon has purely been observed in mainland Europe.
Reports of similar incidents have caused France, Sweden, Finland, Canada and most recently Germany to recommend that younger people, who are much more likely to be affected by the condition, avoid the shot. In Norway and Denmark, the vaccine is still suspended.
The main condition causing alarm is called cerebral venous sinus thrombosis, when blood forms clots in the veins that run from the brain, a potentially fatal complication.
In the cases of concern, this has been combined with an issue called thrombocytopenia where a patient also presents abnormally low levels of platelets, resulting in heavy bleeding.
In Norway, health officials have reported at least six such cases among 120,000 recipients of the jab, four of whom died. In Germany, 31 cases have been reported after 2.7m vaccinations, including 29 women aged between 20 and 63, and two men aged 36 and 57. Nine of them have died.
Up to and including March 24, the MHRA has received 22 reports of CVST and eight reports of other thrombosis events coupled with low platelets, out of a total of 18.1m people who had received the AstraZeneca vaccine. This equates to roughly one case in every 600,000 recipients.
In the UK, 17 more reports of CVST have been made this week compared with the previous week.
Officials in the UK said there was insufficient evidence at the moment to make any changes to the vaccination policy. Even if a causal link were established, some UK-based experts said it would still make sense to continue with vaccinations as the blood clot incidents appeared to be extremely rare.
Johannes Oldenburg, professor of transfusion medicine at Bonn university, said he agreed with the UK’s decision, even though he believed the AstraZeneca shot was causing the symptoms.
“If I had a choice between immediate vaccination with AstraZeneca or waiting four weeks for Moderna, then I would choose the AstraZeneca vaccine because the four weeks of protection far outweighs this risk,” he said.
Oxford university and AstraZeneca said their trials showed the vaccine was safe and effective, and that they were continuing to monitor for side effects as the shot was rolled out.
Dr June Raine, chief executive of the MHRA, reiterated that “the benefits of Covid-19 vaccine AstraZeneca in preventing Covid-19 infection and its complications continue to outweigh any risks and the public should continue to get their vaccine when invited to do so”.