Head of vaccines at the European Medicines Agency (EMA) says he believes there is a link between AstraZeneca's COVID-19 vaccine Vaxzevria, also known as AZD1222, and rare cases of thrombosis that have been reported in people who recently received it. In an interview published Tuesday in Il Messaggero newspaper, Marco Cavaleri stated "in my opinion we can now say…it is clear there is a link with the vaccine, but we still do not know what causes this reaction."
Several countries suspended use of the vaccine last month amid reports of these rare blood clots, and while an initial review by the EMA found no higher risk of thromboembolic events overall, it could not definitively rule out a causal link to very rare cases of blood clots associated with thrombocytopenia. Specifically, the EMA highlighted cases of cerebral vein thrombosis (CVT) as well as disseminated intravascular coagulation that had occurred – mostly in women under the age of 55 – at a higher rate than the general population. The agency ultimately concluded on March 18 that the benefits of Vaxzevria outweigh any risks, but said it would continue to probe the matter.
"These platelet-deficient cerebral thromboses appear to be the main event to investigate," remarked Cavaleri, adding that the EMA would be saying in an update that a "connection exists, but we still have to understand how this happens." He said that while he still believes the vaccine's benefits outweigh its risks, the effects on different age groups must be examined "in more detail…Very meticulous work will be needed to understand if the risk-benefit ratio is in favour of the vaccine for all ages."
Germany last week temporarily halted use of Vaxzevria in people under 60 amid further reports of CVT in the country among recipients, including some fatalities. Its vaccine commission STIKO has also advised against people under 60 getting their second dose of AstraZeneca's product, saying they should be receiving an mRNA-based vaccine instead "until…appropriate data [are] available." France and Canada have also limited Vaxzevria to older populations.
Meanwhile, other reports have suggested that the UK – which so far has not paused rollout of the AstraZeneca vaccine – may advise people under the age of 30 not to take it. The MHRA has said that as of March 24, there were 30 cases of CVT and eight other thrombosis events with low platelets among 18.1 million people in the UK so far given Vaxzevria. Seven of the cases were fatal.
Cavaleri stated that the EMA's evaluation of Vaxzevria is "far from over," and that it was for individual countries in the EU to set up specific guidelines around which age groups were given which vaccines. Meanwhile, a spokesperson for the EMA said the agency's Pharmacovigilance Risk Assessment Committee (PRAC) had "not yet reached a conclusion and its review is currently ongoing," with an update assessment expected on Wednesday or Thursday. "We are trying to get a precise picture of what is happening, to define in detail this syndrome due to the vaccine," Cavaleri added.
AstraZeneca said recently its vaccine was 76% effective at preventing symptomatic COVID-19 in a Phase III trial of 32,449 participants conducted in the US, including 85% efficacy in adults 65 years and older. It also noted there were no safety flags identified by an independent data safety monitoring board, including no higher risk of thrombosis or events characterised by thrombosis, as well as no instances of CVT.
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