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The largest study published to date on some post-vaccine side effects found that people had a slightly higher than normal risk of blood clots after receiving an AstraZeneca or Pfizer-BioNTech vaccine. But the study found that the same coagulation conditions were significantly more likely to occur among people infected with the coronavirus — and over longer periods of time.
With Another study from Israel this weekData published Thursday night in The British Medical Journal added to growing evidence that although coronavirus vaccines are associated with some rare side effects, these risks are overshadowed by risks from Covid-19.
The study was based on the electronic health records of more than 29 million people in the UK. It went beyond previous analyzes in finding a link not only between very rare coagulation conditions and the AstraZeneca vaccine, but also between these conditions and the Pfizer vaccine. Previous studies have identified increased risks of clotting after the AstraZeneca vaccine, but not after the Pfizer vaccine.
In interviews, the new paper’s co-authors said the number of these cases they’ve identified — involving clots blocking a vessel that drains blood from the brain — is small enough that further study is needed. The study said that even the increased risk of these clots far outweighs the chances that people will develop them after being infected with the virus itself.
“The risks of these events are very rare, although there are some risks,” said Aziz Sheikh, co-author of the study and professor of primary care research at the University of Edinburgh in Scotland. “And the biggest point is that the risks associated with Covid-19 are indeed orders of magnitude higher.”
The study examined electronic health records of people given their first dose of coronavirus vaccine in the first five months of the UK’s vaccination campaign. Of those 29 million people, about 1.8 million also tested positive for coronavirus before or after they were vaccinated. The study compared the risk of blood clots shortly after vaccination with the risk at other periods, as well as weeks after someone developed Covid-19.
After the first shot of the AstraZeneca vaccine, people were at a slightly higher risk for certain blood clots, as well as a condition characterized by a low platelet level that may predispose them to abnormal bleeding. The first shot of the Pfizer vaccine put people at a slightly higher risk of stroke caused by blockages within a blood vessel.
And both vaccines have been linked, though in low numbers, to very rare clots that prevent blood from flowing out of the brain.
Even so, these risks were much smaller than those linked to the development of Covid-19. For example, for every 10 million people given the first dose of the AstraZeneca vaccine, about 66 more people than normal will develop a clot that starts in a vein, the authors said. But in the same number of people infected with the virus itself, 12,614 more people than normal will develop these clots.
In the United States, between 300,000 and 600,000 people a year develop blood clots in their lungs or leg veins or other parts of the body, according to the CDC. those who were vaccinated by chance, unrelated to the vaccine.
Understand the Vaccine and Mask Instructions in the US
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- vaccination rules. On August 23, the Food and Drug Administration Pfizer-BioNTech’s coronavirus vaccine granted full approval It paves the way for people aged 16 and over to increase their tenure in both the public and private sectors. became private companies increasingly mandatory vaccines for employees. Such powers legally allowed and upheld in court appeals.
- Mask rules. Centers for Disease Control and Prevention in July suggested The fact that all Americans, regardless of vaccination status, wear masks in public in areas with outbreaks was a reversal of the guidance it presented in May. See where the CDC guidance applies, and where states created their own mask policies. The battle over masks has become contentious in some states. local leaders defying state bans.
- Colleges and universities. More than 400 colleges and universities require their students to be vaccinated against Covid-19. Nearly all in states that voted for President Biden.
- Schools. Both of them California and New York City imposes vaccination requirements for education personnel. A survey published in August found that many American parents with school-age children are against compulsory vaccinations for students, but More support for mask missions for unvaccinated students, teachers and staff.
- Hospitals and medical centers. Many hospitals and major healthcare systems require their employees to be vaccinated against Covid-19. By citing increased caseloads fueled by the delta variant and stubbornly low vaccination rates in their communities, even within the workforce.
- New York City. Proof of vaccination is required for workers and customers. indoor dining, gyms, performances and other indoor situations, but the app doesn’t start until September 13. Teachers and other education workers The city’s large school system will need at least one dose of the vaccine by September 27, with no weekly testing option. City hospital staff they should also be vaccinated or undergo weekly tests. Similar rules apply to New York State employees.
- at the federal level. The Pentagon has announced that it will try to make coronavirus vaccines mandatory for the country. 1.3 million active-duty soldiers No later than mid-September. President Biden announced all civilian federal employees would have to get vaccinated against coronavirus or subject to regular testing, social distancing, mask requirements and restrictions on most trips.
Some countries have restricted the use of the AstraZeneca vaccine after a small number of people vaccinated in Europe became seriously ill or died from a very rare condition characterized by both clotting and abnormal bleeding.
Carol Coupland, co-author of the latest study and professor of medical statistics affiliated with both the University of Oxford and the University of Nottingham, said the study was unable to assess this precise situation because the researchers did not have enough detailed readings. platelet counts of patients.
The finding of a slightly higher risk of clotting after the Pfizer vaccine contradicts other analyzes, including: Article published in the New England Journal of Medicine from Israel This week. The study from England included many more people, allowing it to fall into the rarer clot categories. It was also designed differently: It studied the same people over time, whereas the Israeli study compared risks in vaccinated and unvaccinated people over the same period.
Ben Reis, co-author of the Israeli study and director of the predictive medicine group at Boston Children’s Hospital Computational Health Informatics Program, said both studies are a testament to the way electronic health records allow researchers to retrieve them quickly. Compare very rare safety signals and risks with those following a coronavirus infection.
“The vaccine decision should not be made in a vacuum,” he said. “The alternative outcome is the real risk of being exposed to the virus without a vaccine. These are the two scenarios that need to be compared.”
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