ZURICH (Reuters) – The European drug regulator on Wednesday said it had found a possible link between AstraZeneca’s COVID-19 vaccine and very rare blood clots in adults who received the injection. Britain recommended that people under 30 get an alternative COVID-19 vaccine if possible.
Here’s what we know so far:
WHAT HAPPENED?
The EMA said its vaccine adverse reaction monitoring system had received 169 reports of cerebral venous sinus thrombosis (CVST), or clots in blood vessels leaving the brain, and 53 cases of splanchnic venous thrombosis (SVT), or clotting in April 4. veins in the abdomen.
That is of the approximately 34 million AstraZeneca vaccine doses administered in Britain and the European Economic Area since the vaccinations began nearly three months ago.
The safety committee investigated 62 cases of CVST and 24 cases of SVT, 18 of which were fatal.
Most of the reported cases have occurred in women under the age of 60, although this can be misleading. Germany and Great Britain say that many more women have received the injection of AstraZeneca than men.
Most cases occurred within 2 weeks of the person receiving the first dose.
German vaccination officials who recorded 29 cases of CVST in women aged 20 to 59 who received the AstraZeneca vaccine said the rate of events in that group within 16 days of vaccination was 20 times higher than would normally have been expected.
The German Ministry of Health has said that there were 1 to 1.4 cases of CVST to be expected at the time.
WHAT HAS THE BRITAIN REGULATOR SAID?
The Medicines and Healthcare products Regulatory Agency assessed 79 cases of rare clotting in combination with low platelets, with 19 deaths – 13 women and 6 men. Eleven of the deaths in people under 50 and three under 30.
All 79 cases occurred after a first dose of the vaccine.
HOW DO REGULATORS MAKE THEIR DECISION?
British officials used statistics from the University of Cambridge’s Winton Center for Risk and Evidence Communication to explain their recommendations that young people get an alternative injection while older people still get AstraZenecas.
According to the Center, vaccination with the AstraZeneca injection would reduce admissions to intensive care units by nearly seven in 100,000 people in the 20-29 year old group at high risk of exposure to the virus, while 1.1 people per 100,000 people in the same group was estimated to be likely to suffer serious vaccine-related harm.
The risk of serious harm from vaccination decreases as the elderly get more, and ICU admissions prevented by vaccination increase sharply, increasing the benefit-risk balance of the AstraZeneca injection. The center concluded that only 0.4 people in every 100,000 in the 50-59 age group would suffer vaccine-related harm, while 95.6 IC admissions per 100,000 people would be prevented.
EMA researchers checked whether the frequency of events was higher in the vaccinated population than normal background figures based on public health statistics or insurance data. This would be combined with a medical analysis of each case and insight from scientific literature.
In its findings, the EMA said on March 18 that only 1.35 cases of CVST could normally be expected in people under 50 within 14 days of receiving the AstraZeneca vaccine, while 12 cases had been recorded on the same cut-off date. .
In comparison, four in 10,000 women would develop a blood clot from oral contraception.
Key to the EMA’s assessment that the benefits still outweigh the risks are its conclusions about the likelihood of an increased risk from clotting, compared to the benefits of preventing COVID-19 and reducing hospitalizations and deaths.
WHAT IS THE EU DOING NOW?
The EMA said unusual low platelet blood clots should be listed as very rare side effects and countries should decide how to proceed with their national COVID-19 immunization campaigns.
These can vary from country to country, the EMA said, depending on factors such as how quickly infections spread and whether vaccines are available. The safety committee asked for new studies and changes to ongoing studies to provide more information about the mechanism behind the rare clots.
AstraZeneca and European regulators have said concerns about blood disorders have not emerged in clinical studies.
ARE THERE THEORIES FOR WHAT CAN LEAD TO THE BELLS?
One of the possible causes for these rare cerebral sinus vein clots under investigation is that in rare cases the vaccine triggers an unusual antibody.
The EMA said the vaccine could trigger an immune response leading to the unusual clotting, although it acknowledged that scientists have not yet identified risk factors that could predispose someone to clotting in combination with low platelets.
German scientists at Greifswald University concluded that the vaccine is linked to the side effects, although their work still requires peer review. Andreas Greinacher, an expert on drug-induced immune responses, said specimens he examined showed unusual antibodies that activate platelets and cause the clots.
Greinacher is still looking for clues as to why some people had blood clots and others didn’t.
Reporting by Ludwig Burger in Frankfurt, Matthias Blamont in Paris and John Miller in Zurich; Additional reporting by Kate Kelland and Alistair Smout in London and Julie Steenhuysen in Chicago; Edited by Josephine Mason and Angus MacSwan