Why was the AstraZeneca coronavirus vaccine suspended in some countries?

France, Denmark, Ireland and Thailand are among the countries where reports of some people developing thromboembolism (blood clots), despite no direct evidence that the vaccine was responsible, prompted the temporary suspension of the Oxford University-developed AstraZeneca coronavirus vaccine.

What is the AstraZeneca–Oxford vaccine?

The AstraZeneca–Oxford vaccine uses a weakened form of the adenovirus that causes upper respiratory tract infections as a vector. Its genetic properties have been modified so that, while it causes infection in chimpanzees, it cannot replicate in the human body. The adenovirus used for the vaccine has also had genetic codes added for production of the protein displayed on the surface of the SARS-CoV-2 coronavirus and important in causing infection: S protein. The aim is for immune system cells to recognize the S protein and generate a response , thereby preventing the virus from entering cells and causing infection.

The AstraZeneca vaccine was approved for use in the United Kingdom and several European Union countries in December 2020. However, it has not yet been approved by the US Food and Drug Administration (FDA), which requested results from a large clinical trial. The study data have actually been published: on the evening of March 24, AstraZeneca, based on a Phase III trial involving more than 32,000 participants, most in the United States, stated that its COVID-19 vaccine was 76 percent effective at preventing symptomatic disease, as it announced. However, there are concerns that allegations of the vaccine causing blood clots could be an obstacle to FDA approval.

Important development: The mechanism of the Oxford–Astrazeneca vaccine’s clotting side effect explained

A report published on April 14 in the leading scientific medical journal NEJM described a study showing that platelet-activating factors developing against PF4 in connection with the Oxford–Astrazeneca (ChAdOx1) vaccine led to immune thrombotic thrombocytopenia.

What are the concerns about the AstraZeneca vaccine?

Denmark was the first country to suspend use of the AstraZeneca COVID-19 vaccine after blood clots were reported in some people, including one person who developed multiple clots and died 10 days after receiving at least one dose. Danish health authorities say the suspension will last at least two weeks while the cases are investigated. “At present, no conclusion can be drawn about whether there is a link between the vaccine and blood clotting.”

Norway, Iceland, Bulgaria, Thailand and Congo soon followed suit. Norwegian officials reported that 4 people aged 50 or younger who had received the AstraZeneca vaccine had abnormally low platelet counts, which can cause serious bleeding. Shortly afterward, Ireland and the Netherlands also announced temporary suspensions of AstraZeneca vaccine use. Most national health authorities emphasize that the suspension is strictly precautionary. Dutch Health Minister Hugo de Jonge: “We must always act cautiously, which is why it makes sense to press the ‘pause button’ now as a precaution.”

Norwegian doctors announced that one person hospitalized after receiving the AstraZeneca vaccine had died. German officials said they would suspend use of the vaccine on the recommendation of drug regulators. France ’s President Emmanuel Macron said use would be suspended until the European Medicines Agency (EMA) had reviewed the vaccine. Slovenia, Spain and Portugal also suspended use of this vaccine. In response to the suspensions, AstraZeneca said it had carefully reviewed data from 17 million people vaccinated across Europe. It said there was no evidence of an increased risk of blood clotting in any age group or sex in any country.

Is there evidence that the vaccine is responsible for blood clotting?

EMA says there is no indication that vaccination caused these conditions, adding that the number of blood-clotting reports among people who received the AstraZeneca vaccine is no higher than among those who did not.

In England,11 million doses of the AstraZeneca vaccine have been administered, more than in other countries. Around 11 people were reported to have developed blood clots after vaccination. In none of them was the vaccine proven to have caused the condition.

Some doctors point out that vaccination campaigns began by vaccinating the most vulnerable and older people, who are already more likely to have health problems, making it difficult to establish whether the vaccine is responsible. Blood clots in the arms, legs or elsewhere can sometimes break free and travel to the heart, brain or lungs, causing stroke, heart attack or a potentially fatal blockage of blood flow.

Why were AstraZeneca vaccinations suspended in many countries?

When vaccines are rolled out widely, scientists expect reports of some serious health problems and deaths, because millions of people are being vaccinated and problems are expected to arise in such a large group. The vast majority are not vaccine-related, but because COVID-19 vaccines are still experimental, scientists must investigate every possibility that a vaccine may have unforeseen side effects. The vaccines were considered experimental because they were developed only in the past year, so none has long-term data.

Is this a concern for other COVID-19 vaccines?

AİA is currently investigating vaccines made by Pfizer-BioNTech, Moderna and AstraZeneca against COVID-19 to determine whether they cause low blood platelet counts, a condition that can lead to bruising and bleeding in some patients.

The proportions of COVID-19 vaccines administered as of March 30, 2021 can be seen below:

Are there other issues with the AstraZeneca vaccine?

The vaccine has been approved for use in adults in more than 50 countries, and its safety and efficacy have been demonstrated in studies in England, Brazil and South Africa. However, there are concerns about how the vaccine data were presented, and some European leaders, including French President Macron, question its efficacy.

England first approved the vaccine on the basis of partial results showing efficacy of around 70%. However, these results were overshadowed by a manufacturing error that caused some participants to receive only a half-dose at their first vaccination, an error the researchers did not immediately acknowledge. When authorization was recommended, EMA estimated vaccine efficacy at around 60%.

Data on whether the vaccine protected older adults were also incomplete, leading some European countries initially not to administer it to older people. In the United States, the Food and Drug Administration (FDA) halted the study of 30,000 Americans for six weeks while information was sought about some possible side effects reported in England.

Dr Paul Hunter, a professor at the University of East Anglia’s medical school, said: “All the data we have seen on the AstraZeneca vaccine show that it is very safe and saves people from COVID-19 deaths. However, this may be more of a perception problem, because whenever there is a vaccine issue, we soon hear the name ‘AstraZeneca’.” he said.

What do experts recommend?

WHO and EMA, along with regulators in several countries, say that people should continue to be vaccinated and that the small risks of vaccination far outweigh any potential harm. “Public safety always comes first. People should still get a COVID-19 vaccine when invited.”

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