The largest published study to date of certain post-vaccination side effects found that people were at slightly higher than normal risk of blood clots after an AstraZeneca or Pfizer BioNTech syringe. However, the same coagulation conditions occurred much more frequently – and over longer periods of time – in people who were infected with the coronavirus, the study found.
Coupled with another study from Israel this week, the data published Thursday evening in the British Medical Journal added to the growing evidence that while the coronavirus vaccines are associated with certain rare side effects, those risks are eclipsed by the risks of Covid be asked. 19th
The study was based on the electronic health records of more than 29 million people in England. It went beyond previous analysis in finding a link not only between very rare coagulation disorders and the AstraZeneca vaccine, but also between those disorders and the Pfizer vaccine. Previous studies had found an increased risk of clotting after the AstraZeneca vaccination, but not after the Pfizer injection.
In interviews, the new paper’s co-authors said the number of cases they discovered – in which clots block a vein that drains blood from the brain – were small enough that further study was needed. Even the increased risk of these clots was far outweighed by people’s chances of developing them after contracting the virus themselves, according to the study.
“While there are some risks, the risks from these events are clearly very rare,” 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 really orders of magnitude higher.”
The study looked at the electronic health records of people who received their first dose of a coronavirus vaccine during the first five months of the UK vaccination campaign. Of these 29 million people, just under 1.8 million people tested positive for the coronavirus before or after the vaccination. The study compared the risk of blood clots shortly after vaccination with the risk during other periods as well as the weeks after someone developed Covid-19.
After receiving the AstraZeneca vaccine for the first time, patients were at slightly increased risk of certain blood clots and a condition characterized by low blood platelet levels, which can make them prone to abnormal bleeding. An initial shot of the Pfizer vaccine appeared to put people at a slightly increased risk of stroke, which is caused by blockages in a blood vessel.
And both vaccines, albeit in small numbers, have been linked to the very rare clots that prevent blood from draining from the brain.
Even so, these risks were far lower than those related to the development of Covid-19. For example, the authors said that for every 10 million people who received a first dose of the AstraZeneca vaccine, about 66 more people than normal would develop a blood clot that begins in a vein. But of the same number infected with the virus itself, 12,614 more people than normal would develop these clots.
In the United States, 300,000 to 600,000 people each year develop blood clots in the lungs, leg veins, or other parts of the body in those who received the injections by accident, unrelated to the vaccine, according to the CDC.
Understand US vaccination and mask requirements
- Vaccination rules. On August 23, the Food and Drug Administration fully approved Pfizer-BioNTech’s coronavirus vaccine for people aged 16 and over, paving the way for increased mandates in both the public and private sectors. Private companies are increasingly demanding vaccines for employees. Such mandates are legally permissible and have been confirmed in legal challenges.
- Mask rules. The Centers for Disease Control and Prevention in July recommended that all Americans, regardless of vaccination status, wear masks in public places indoors in areas with outbreaks, reversing the guidelines offered in May. See where the CDC guidelines would apply and where states have implemented their own mask guidelines. The battle over masks is controversial in some states, with some local leaders defying state bans.
- College and Universities. More than 400 colleges and universities require a vaccination against Covid-19. Almost all of them are in states that voted for President Biden.
- schools. Both California and New York City have introduced vaccine mandates for educational staff. A survey published in August found that many American parents of school-age children are against mandatory vaccines for students but are more likely to support masking requirements for students, teachers and staff who are not vaccinated.
- Hospitals and medical centers. Many hospitals and large health systems require their employees to have a Covid-19 vaccine, due to rising case numbers due to the Delta variant and persistently low vaccination rates in their communities, even within their workforce.
- New York City. Proof of vaccination is required by workers and customers for indoor dining, gyms, performances, and other indoor situations, though enforcement doesn’t begin until September 13. Teachers and other educational workers in the city’s vast school system are required to have at least one vaccine dose by September 27, with no weekly testing option. City hospital staff must also be vaccinated or have weekly tests. Similar rules apply to employees in New York State.
- At the federal level. The Pentagon announced that it would make coronavirus vaccinations compulsory for the country’s 1.3 million active soldiers “by mid-September at the latest. President Biden announced that all civil federal employees would need to be vaccinated against the coronavirus or undergo regular tests, social distancing, mask requirements and travel restrictions.
Some countries restricted the use of the AstraZeneca vaccine after a small number of people in Europe who received an injection became seriously ill or died of a very rare disease characterized by both clotting and abnormal bleeding.
Carol Coupland, a co-author of the latest study and professor of medical statistics at the University of Oxford and the University of Nottingham, said the study could not assess this exact condition because the researchers did not provide detailed enough readings of the patients’ platelet counts.
The finding of a slightly increased risk of clotting after the Pfizer vaccine contradicted other analyzes, including the article from Israel published this week in the New England Journal of Medicine. The study from England included far more people, which enabled her to look at rarer categories of clot. It was also designed differently: it examined the same people over a longer period of time, while the Israeli study compared the risks in vaccinated and unvaccinated people over the same period of time.
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 were evidence of how electronic health records enabled researchers to quickly self-capture very rare safety signals and compare the risks with those after a coronavirus infection.
“The vaccination decision shouldn’t be made in a vacuum,” he said. “The alternative outcome is the very real risk of exposure to the virus without vaccination. These are the two scenarios that should be compared. “