Blood Clots and AstraZeneca Vaccine: What You Need to Know

AstraZeneca: 30 cases of blood clots among vaccinated 0:46

(CNN) – The UK drug regulator reported that at least 30 people there have suffered rare types of blood clots after receiving the Oxford-AstraZeneca coronavirus vaccine, but cautioned that it is too early to tell if the vaccine itself it is the one that triggers clots.

The Medicines and Healthcare Products Regulatory Agency (MHRA) said in a statement Thursday night 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 out of a total of 15.8 million people who had received at least one dose of the vaccine by March 21. A breakdown of CVST data compiled by the MHRA showed that four people had died, but the agency did not immediately respond to questions from CNN to confirm whether there were any fatalities.

The agency advised the UK to continue to administer the vaccine to all groups, arguing that such clotting incidents are very rare and that the benefits still largely outweigh the risks, joining similar assessments by the European Medicines Agency (EMA). and the World Health Organization (WHO).

But there are more and more reports of blood clots from different countries, particularly in Europe, where the AstraZeneca vaccine is widely used. Some countries have chosen to stop the vaccine altogether, while others have limited its use to certain age groups.

This is what you should know.

AstraZeneca: UK backs vaccine 0:38

Where else does this happen?

The Netherlands said on Friday it would stop giving the vaccine to people under 60 as a “precautionary measure” after the country’s drug authority reported blood clots among women between the ages of 25 and 65. The country has distributed 400,000 doses of the vaccine so far.

Germany had previously done so, which on Tuesday followed suit after 31 CVST reports. 29 of the 31 were women between the ages of 20 and 63, and nine of the patients died, according to a Reuters report citing the country’s drug regulator.

At least 2.7 million Germans have been vaccinated with a first dose of AstraZeneca, which means that CVST cases are still relatively low. Complications have been reported in one in 100,000 AstraZeneca vaccines, according to the country’s Ministry of Health. He did not detail what those complications were and how serious they were.

As of March 30, Norway had reported three deaths in people who experienced a combination of blood clotting, low platelet counts and bleeding three to 14 days after receiving the vaccine, the country’s medicine agency said in a report. . Norway has administered at least one dose of AstraZeneca to more than 134,000 people.

“The Norwegian Medicines Agency believes there is a probable link to the vaccine, but we need more research to clarify exactly what is causing this,” he wrote.

Denmark reported two cases of blood clots and low platelet counts after vaccination; one of the cases was fatal.

How can scientists determine if there is a link?

An indicator to take into account is incidence. Blood clots in general are so common that a certain number of people are expected to contract them for various reasons on any given day of a given week. If someone has received a vaccine and then develops a blood clot, it does not necessarily mean that the vaccine injection caused the clot.

After initial reports of clotting last month, AstraZeneca was quick to point out that the incidence of clots in general is lower in people who have received the injection than in the general population, in the countries that use it.

An AstraZeneca spokesperson told CNN in a statement on Friday: “Patient safety remains the company’s top priority,” and referred to UK, European Union authorities and WHO recommendations to continue its use.

“The risk-benefit profile of the vaccine was reaffirmed in the EMA’s monthly safety update,” the spokesperson said.

To get a clearer picture, scientists look more specifically at the types of clots that are reported. CVST is rare to begin with, and it is usually not difficult to determine whether the incidence of a blood clot has increased. In this case, however, it is a bit confusing, in part because the CVST rate in the population is not specified in the first place.

The MHRA said that 15.8 million people had 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.

“So the absolute risk of CVST after this vaccine is still extremely low … and it is not clear if it is higher than the usual expected incidence of CVST,” David Werring of the UCL Institute of Neurology told the Science Media Center.

He noted that the usual incidence of CVST in the UK was probably around 5 to 15 per million each year, but added that those figures vary due to the difficulty of diagnosing some cases.

What has become a more useful approach for scientists is the nature of these blood clots. Emerging evidence suggests that some cases of blood clots after vaccination have unusual characteristics. While these patients experience blood clots, they unusually also exhibit symptoms of thrombocytopenia, a low count in the same blood platelets that generally prevent clotting, noted the EMA and several other health experts in the region.

“This raises the possibility that the vaccine may be a causative factor in these rare and unusual cases of CVST, although we do not know this yet, so more research is urgently needed,” Werring said.

AstraZeneca, hero or villain? 1:19

Experts keep saying the benefits outweigh the risk, but by how much?

If you look at this globally, or even nationally, the answer is: a lot.

Consider this. Since the UK began vaccinating people on December 7 to March 21, there have been 30 cases of rare blood clots, four of which were fatal. In that same time period, more than 2.5 million people contracted COVID-19 and 63,082 people in the country died from the virus, government data shows.

“It is vital that the vaccination process is not delayed,” said David Spiegelhalter, president of the Winton Center for Evidence and Risk Communication at the University of Cambridge.

He pointed to a model that showed that even with the current low levels of the virus, delaying the vaccination of 500,000 people between the ages of 44 to 54 would likely lead to around 85 hospitalizations and probably five deaths.

But these dynamics can look different when data by gender and age is taken into account.

Spiegelhalter said that “it is important to know if this risk is substantially higher in younger age groups, as has been found elsewhere. Vaccinating younger people is both for the wider community and for their direct benefit, so it is reasonable to try to avoid causing harm, even if it is extremely rare. ‘

Covid-19, in general, has had more serious health consequences for older age groups. But hospitalization figures in various parts of Brazil and the United States suggest that younger people are becoming more susceptible to serious illnesses than before. It is not known whether the new variants are motive, vaccination levels, behavior, or a combination of many factors.

Are these blood clots likely to be fatal?

The reported figures are so miniscule that it is difficult to draw conclusions about death rates. In Germany, 9 of the 31 CVST cases were fatal. In the UK, 4 were.

A group of blood clotting experts investigating possible links between the vaccine and nine cases in Germany has said that the presence of clotting with low blood platelet counts in these people resembles a known blood disorder called heparin-induced thrombocytopenia (HIT). ), which is “treatable if identified promptly,” the experts said in a draft of the study, which has not yet been peer-reviewed. It is a condition that occurs as an adverse reaction to heparin, a blood-thinning drug that is often used to treat CVST.

Andreas Greinacher of the University of Greifswald presented some of the group’s findings to journalists this week, calling what he believes to be a “vaccine-induced prothrombotic immune thrombocytopenia” or VIPIT reaction. The group will ask medical professionals to refrain from using heparin in patients with blood clots if they have received the AstraZeneca injection, as the drug could make their condition worse.