Millions of people in dozens of countries have received the AstraZeneca Covid vaccine with few adverse effects reports, and tens of thousands of people have previously tested it to be safe.
But recently, blood clots and abnormal bleeding in a small number of vaccines in European countries have called into question their safety, although no causal link has been found between the patient’s conditions and the vaccine. The reports have asked more than a dozen countries to suspend the use of the vaccine in part or in full while the cases are being investigated. Most countries said they were doing this as a precaution until leading health care institutions could review the cases.
The AstraZeneca vaccine has not yet been approved for use in the United States, although a review of the US trial is expected soon.
What kind of problems caused the countries to take precautionary measures?
The cascade of decisions to suspend the use of AstraZeneca’s vaccine, mainly by European countries, followed reports of four serious cases in Norway, which were described among health workers under 50 who received the vaccine. The health authorities there said that most had blood clots or bleeding disorders and that they had a low platelet count. Two of them died of cerebral hemorrhage, and the other two were admitted to hospital. The deaths of a 60-year-old woman in Denmark and a 57-year-old man in Italy also prompted quick decisions, although none of the deaths were fully investigated to determine whether the shots they received were related. .
What is a blood clot and what causes it in general?
A blood clot is a thickened, gelatinous blood stain that can block circulation. Clots form in response to injuries and can also be caused by many diseases, including cancer and genetic disorders, certain drugs and prolonged sitting or bed rest. Clots that form in the bones sometimes break down and move to the lungs or brain, where it can be fatal.
Can the vaccine cause blood clots?
Vaccines have not been shown to cause blood clots, said Daniel Salmon, director of the Institute for Vaccination at Johns Hopkins University.
Blood clots are common in the general population, and health authorities suspect that the cases reported to vaccine recipients are most likely accidental and unrelated to the vaccination.
“There are many causes of blood clotting, many predisposing factors and many people who are at increased risk – and it is often the people who are currently being vaccinated,” Mark Slifka, a vaccine researcher, told Oregon Health and Science University.
Of 300,000 to 600,000 people each year in the United States develop blood clots in their lungs or in veins in the legs or other body parts, according to the Centers for Disease Control and Prevention.
According to Stephan Moll, a hematologist and professor of medicine at the University of North Carolina, there are approximately 1,000 to 2,000 blood clots in the American population daily.
“The United States has 253 million adults,” said Dr. Moll said. “So, if 2.3 million people in the United States are vaccinated Covid every day, that means about 1 percent of the adult population is vaccinated every day.”
To calculate further, he said, about 1 percent of the daily 1,000 to 2,000 blood clots – 10 to 20 a day – in the vaccinated patients would occur only as part of the normal background figures, which are not related to the vaccine.
“Only if epidemiological data show that the rate is higher would one begin to wonder about a causal link,” said Dr. Moll said.
What can existing data on the AstraZeneca vaccine tell us?
Dr. David Wohl, director of the vaccine clinic at the University of North Carolina, said he saw no evidence that any of Covid’s vaccines caused blood clots, also called thrombosis, in the major clinical trials that led to their authorization. .
But dr. Wohl also remarked: “There are differences between trials and real life.”
The most extensive safety results from the introduction of the AstraZeneca vaccine come from the UK, where 9.7 million doses of the vaccine was handed out last month. The data from the UK found that, although extremely rare, at least some coagulation conditions were equally common for people vaccinated with AstraZeneca’s vaccine compared to those who received Pfizer’s product. But abnormally low platelet levels were more common among people who received AstraZeneca vaccine.
Outside of trials, the vaccines are given to a wider variety of people. So if there are questions about safety when a vaccine is used more commonly, the questions should be investigated, said dr. Wohl said.
“We do not want to ignore a signal that could indicate a bigger problem,” he said. “But at this point it is premature to think that AstraZeneca is causing thrombosis.”
Do vaccines cause other bleeding disorders?
Other vaccines, especially those given to children with measles, mumps and rubella, have been linked to temporarily reduced platelets, a blood component that is essential for clotting.
Decreased platelet levels have been reported in small numbers of patients receiving the Moderna, Pfizer-BioNTech and AstraZeneca vaccines. One recipient, a doctor in Florida, died of a brain hemorrhage when his platelet level could not recover, and another was admitted to the hospital. U.S. health officials said the cases are being investigated, but they have not reported the findings of the reviews and have not yet indicated that there is any connection to the vaccines.
How will investigators determine if there is a link?
The European Medicines Agency Said Monday that it has worked with AstraZeneca and health authorities to investigate ‘all available data and clinical circumstances surrounding specific cases’.
The authorities did not specify what the assessment would look like. However, when assessing a possible link between a vaccine and a serious side effect, researchers generally focus on estimating how often such medical problems will occur by chance in the group of people involved.
This may mean looking at people in the same group before they are vaccinated. It could also mean that we are looking at a similar group of people. If the rate of these problems is higher in the vaccinated group than would be expected in a comparable population, it is a sign that the safety issue may be real, or at least worth more.
Such investigations usually do not depend on definitively determining whether the vaccine was the cause of a death or a serious medical problem, because in most cases it cannot be definitively determined. However, researchers do consider clinical history, such as whether someone has been treated for similar medical problems before being vaccinated.
Researchers also keep in mind factors that increase the risk of a group of people becoming ill. Older people, who have been at the forefront of vaccination campaigns around the world, are at higher risk of developing blood clots than younger people.
Individual health ministries are also conducting investigations, and the health authorities in the countries are awaiting results of autopsies. In Italy, authorities also seized doses of the vaccine in the Piedmont region as part of an investigation into the teacher’s death at the weekend.
Can we expect updates on the investigation?
An advisory committee of the World Health Organization plans to meet on Tuesday to discuss the vaccine. The safety committee of the European Medicines Agency will meet on Thursday.
Jennifer Nuzzo, an epidemiologist at the Center for Health Security at Johns Hopkins University, said she hopes the authorities will provide regular information on the status of investigations into the safety of the AstraZeneca vaccine – something that often does not happen. if safety issues do not occur. investigation.
“I really wish there could be more ongoing communication about what kinds of analyzes they do, what they look at, even if it’s in the meantime – just to give transparency in the process to improve trust in the process,” said Dr. Nuzzo said.
What did the company say about the security scare?
AstraZeneca first addressed security issues in public to Austria a week ago stopped vaccinations of a group of AstraZeneca’s vaccine. A company spokesman at the time said no serious side effects from vaccines had been confirmed.
On Thursday, after Denmark stopped all vaccinations with the AstraZeneca product, the company issued a statement defending the safety of its vaccine more clearly. The safety data from AstraZeneca, which contains more than 10 million records, shows no evidence of an increased risk of blood clot-related problems in any demographic group or country.
Sunday, after several more countries announced plans to suspend their vaccination campaigns, AstraZeneca a news release issued with more details on the number of side effects reported and people vaccinated in clinical trials and vaccination campaigns in Europe.
A spokesman for AstraZeneca said on Monday that the company was working with national health authorities and European officials and was looking forward to their review later this week. (The company refused to name the spokesman.)
Are there precedents for a vaccine safety scare?
Concerns about earlier safety times are usually not confirmed by the evidence, although there are exceptions. In 1999, the first vaccine against rotavirus infection to cause diarrhea in infants deducted from the market because it has been found to increase the risk of bowel obstruction.
But even unfounded security issues have eroded public confidence.
After the Food and Drug Administration approved a highly effective vaccine for Lyme disease in 1998, media reports and a class action lawsuit sparked complaints from people who said they had developed arthritis after being vaccinated. In 2001, the FDA convened a panel of experts to review the vaccine’s safety data – clinical trials showed no difference in the frequency of long-term joint symptoms between the vaccine and placebo groups – and concluded that the vaccine the market must remain.
But then the perception of the vaccine was too far gone: a sharp decline in sales prompted the manufacturer of the vaccine, GlaxoSmithKline, to withdraw the vaccine from the market in 2002.
What is the status of the vaccine in the United States?
Although more than 70 countries approved the vaccine, the United States did not. AstraZeneca has not yet applied for approval from the Food and Drug Administration and is awaiting the results of the US trial that entered more than 32,000 participants.
An announcement from AstraZeneca on the results may come soon: the details of the trial are being investigated by an independent panel of experts, Dr Francis Collins, director of the National Institutes of Health, told Reuters Monday.
Geoffrey Porges, an analyst at investment bank SVB Leerink, says strong results from the safety and efficacy of the trial could reassure people a lot about the AstraZeneca vaccine.
“But the longer it hangs there, without a comprehensive review and without the U.S. Phase 3 results, the more people are going to worry,” he said. Porges said.