The Medicines and Health Products Regulatory Agency (MHRA) said in a statement on Thursday that it received 22 reports of cerebral venous sinus thrombosis (CVST), where clotting forms in the sinuses that drain blood from the brain, and eight other reports of thrombosis. of a total of 15.8 million people who received at least one dose of the vaccine by March 21. An analysis of the MHRA’s CVST data showed that four people died, but the agency did not immediately respond to CNN’s questions to confirm whether there were fatalities.
But more and more reports of blood clots from different countries are emerging, especially in Europe, where the AstraZeneca vaccine is widely used. Some countries are choosing to suspend the vaccine completely, while others have limited its use to certain age groups.
Here’s what you should know.
Where else is this happening?
The Netherlands announced on Friday that it would stop administering the vaccine to people under 60 as a “precautionary measure” after the country’s pharmaceutical authority reported blood clots among women aged 25 to 65. .
“The Norwegian Medicines Agency believes there is a likely link to the vaccine, but we need more research to clarify exactly what is causing it,” he wrote.
Here’s what else you should know.
How can scientists determine if there is a link?
One indicator to be observed is the incidence rate. Blood clots in general are so common that a number of people are expected to contract them for various reasons on any day of the week. If someone has had a vaccine and then developed a blood clot, it does not necessarily mean that the injection caused the clot.
After initial reports of clots last month, AstraZeneca was quick to point out that the incidence of clots in general is lower in people who received the injection than in the general population in countries that are using the injection.
An AstraZeneca spokesman said in a statement to CNN on Friday: “Patient safety remains the company’s highest priority”, and pointed to authorities in the UK, the EU and WHO recommendations to continue its use. .
“The risk-benefit profile of the vaccine was reaffirmed in the monthly EMA safety update,” said the spokesman.
To get a clearer picture, scientists are looking more specifically at the types of clots reported. CVST is rare to begin with and it is usually not difficult to find out if the incidence of a blood clot event has increased. In this case, however, it is somewhat obscure, in part because the rate of CVST in the population is unclear in the first place.
The MHRA said 15.8 million people received at least one injection of the AstraZeneca vaccine in the UK. With 30 cases of CVST or other thrombosis in the UK, the incidence of developing one of these rare clots is 1.89 in a million.
“Therefore, the absolute risk of CVST after this vaccine remains extremely low … and it is not clear whether this is greater than the usual expected incidence of CVST,” David Werring of the UCL Institute of Neurology told the Science Media Center.
He said that the normal incidence of CVST in the UK was probably around 5 to 15 in a million each year, but added that these figures vary due to the difficulty in diagnosing some cases.
What has become a more useful focus for scientists is the nature of these blood clots. New evidence suggests that some cases of blood clots after vaccination have unusual characteristics. Although these patients have blood clots, they also uncommonly show symptoms of thrombocytopenia – a low blood platelet count that usually prevents clotting, EMA and several other health experts in the region noted.
“This raises the possibility that the vaccine could be a causative factor in these rare and uncommon cases of CVST, although we don’t know that yet, so more research is urgently needed,” said Werring.
Experts keep saying that the benefits outweigh the risks, but by how much?
If you look at this on a global, or even national, level, the answer is: a lot.
Consider this. Since the UK started vaccinating people on 7 December until 21 March, there have been 30 cases of rare blood clots, four of which are fatal. In the same period, more than 2.5 million people caught Covid-19 and 63,082 people died in the country with the virus, government data show.
“It is vital that vaccination implementation is not delayed,” said David Spiegelhalter, president of the University of Cambridge’s Winton Center for Risk and Evidence Communication.
He pointed to a model that showed that even with current levels of the virus, postponing the vaccination of 500,000 people between 44 and 54 years old would likely lead to around 85 hospitalizations and probably five deaths.
But these dynamics may appear different when data by sex and age are taken into account.
Spiegelhalter said that “it is important to know whether this risk is substantially greater in younger age groups, as has been found elsewhere. Vaccination of younger people is both for the community at large and for its direct benefit, and so it is reasonable to try to avoid causing damage, even if extremely rarely. ”
Covid-19, in general, had more serious consequences for the health of older age groups. But the numbers of hospitalizations in various parts of Brazil and the United States suggest that young people are becoming more susceptible to serious illnesses than before. It is not known whether the new variants are the reason, vaccination levels, behavior or a combination of many factors.
Can these blood clots be fatal?
The numbers that arrive are so small that it is difficult to draw conclusions about mortality rates. In Germany, nine of the 31 cases of CVST were fatal. In the UK, four were.
Andreas Greinacher of the University of Greifswald presented some of the group’s findings to journalists this week, calling what he thinks is a reaction to the injection “vaccine-induced prothrombotic immune thrombocytopenia”, or VIPIT. The group is calling on medical professionals to avoid the use of heparin in patients with blood clots if they have received the AstraZeneca injection, as the drug can worsen their condition.