What we know: AstraZeneca Vaccine and Blood Clots

Introduction

The AstraZeneca vaccine has been distributed to 115 countries and it represents a vital part of the WHO-led Covax initiative, which aims to provide vaccines doses globally, especially to developing countries that have been left out in the vaccine race. The AstraZeneca vaccine was supposed to represent around 50% of the global vaccine supply in lower-middle-income nations and a third of the supply in low-income nations, however, as growing concerns over it causing a rare blood clot disorder, countries have started to look for other alternatives.

Research on the risks

A few weeks ago, the link between receiving the AstraZeneca jab and developing blood clots appeared to be strictly circumstantial, however, as more and more cases have started to emerge, governments all over the world decided to investigate the matter.

The European Medicines Agency (EMA) has analyzed 86 cases of the rare blood clot disorder, registered up to 22 March, that have occurred in the European Economic Area (the EU, Iceland, Norway and Liechtenstein), out of which most have been reported in women under the age of 60, however, the EMA executive director Emer Cooke has stated there was no available evidence of "specific risk factors such as age, gender, or previous medical history of clotting disorders". Out of the 86 cases, 62 presented blood clots in the major blood vessels of the brain, while 24 involved blood clots that had been formed in one or more abdominal veins. Eighteen cases were in total fatal. Following its research, the EMA has concluded that there is a "possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within two weeks of vaccination" with the AstraZeneca jab. Hence, the EMA’s Safety Committee has concluded that unusual blood clots with low blood platelets should be listed as very rare side effects of the AstraZeneca vaccine.

The EMA has ruled that the benefits of the AstraZeneca vaccine outweigh the risks and Ms Cooke has added, during a press briefing, that "This vaccine has proven to be highly effective - it prevents severe disease and hospitalisation, and it is saving lives."

Possible theories

It has been suggested that the blood clots result from a rare immune reaction to the vaccine, the recipients of the vaccine who developed the clotting disorder having produced antibodies that activated their platelets (cells that are involved in the blood clotting process) and led to the clots. Researchers in Germany and Norway are calling the unusual reaction “vaccine-induced immune thrombotic thrombocytopenia,” or VITT, and it appears to be similar to another relatively rare but serious clotting condition caused by the use of a blood thinner called heparin. Both of these cause a unique immune response, producing antibodies to a complex of heparin and a protein called “platelet factor 4”, triggering this dangerous clotting.

It is currently unclear as to exactly what causes these blood clots, however, researchers have extended some plausible theories. “One is that some people are already predisposed to this condition because of previous bacterial or viral infections,” stated Dr Jose Perdomo, a senior research officer in the haematology research unit at the University of New South Wales St George and Sutherland clinical school.

How high are the risks?

In the UK and the European Economic Area, there have been registered 222 cases of these rare blood clots, to about 34 million people had received the AstraZeneca vaccine in those countries. Hence, the occurrence of this rare side effect has been estimated to be around 1 in 100,000 cases, however, British officials have reported a somewhat lower incidence, which could be a result of them having begun their roll out for this vaccine in older population groups, who, according to some researchers, appear to be less susceptible to developing this syndrome. As the forming of blood clots, in this case, is an immune response, it is more likely to affect young people, who have a stronger immune system.

Discussions have emerged across internet platforms comparing the risk of developing blood clots from the AstraZeneca jab and the significantly higher risk of developing them from contraceptive pills, which are estimated to affect 1 in 1,000 women yearly. However, what is important to note is that, even though the overall incidence of cases is higher in the latter situation, the blood clots that can be produced after being administered the AstraZeneca vaccine are far more dangerous, as they most often affect major arteries in the body and blood vessels in the brain and are frequently followed by haemorrhaging, causing damage in the same way a haemorrhagic stroke would. In some cases, as it has been outlined above, such blood clots may even prove to be fatal.

It is important to also note that new research has found a link between COVID-19 and lower extremity arterial thrombosis, which is a life-threatening blood clot, that often results in amputation or death. It has proven to be more common in people aged over 60, hence, it is almost certain that the benefits of getting the AstraZeneca vaccine outweigh the risks in this population group, however, it is still uncertain whether they do so in younger age groups.

What actions have been taken

Many countries in Europe and across the globe have started restricting the use of the AstraZeneca vaccine, in spite of the EMA’s report that its proven benefits in preventing COVID-19 outweigh the risks. Germany, the Netherlands, the Philippines, Portugal and Spain have recommended that the AstraZeneca vaccine be given only to people over 60. Canada and France have limited it to those over 55; Australia, over 50; and Belgium, over 56. Even though Britain, where the vaccine is produced, has been its staunchest defender, it has decided to offer alternative shots to people under 30.

There have been countries that have even stopped altogether its use, such as Norway and Denmark, and the Democratic Republic of Congo has also taken the decision to delay the start of their inoculation program, as they would have had to rely on the AstraZeneca vaccine doses.

Moreover, the AstraZeneca vaccine requires the administration of two doses in order to be fully effective and, while some countries, such as Italy, are continuing to administer second doses, regulators in France and Germany have recommended the use of another vaccine for the second dose, in the case of people under 55 and 60, respectively.

Consequences and conclusions

As concerns over blood clot risks being caused by the AstraZeneca vaccine, the public has started to grow wary of it, many who were eager to get vaccinated now turning it down, fearing the possible side effects. Since March 28, when Lebanon began administering the first 33,600 AstraZeneca doses supplied by Covax, around a third of those given appointments at the government’s largest hospital have not shown up, said Firas Abiad, the hospital’s chief administrator. When staff called people to ask why, they cited their mistrust of the AstraZeneca vaccine, he said.

According to a new YouGov poll, 61% of people in France now believe that the AstraZeneca vaccine is unsafe, with Germany following closely at 55% - such opinions may strongly affect the overall vaccine rollout, since, given the affordability of the AstraZeneca vaccine, it was supposed to represent a key piece in the inoculation global program.

If countries are to solely rely on the Pfizer and Moderna vaccines, prospects for achieving herd immunity in the next year are quite bleak, as “high-income countries,” including the United States, account for just 16 per cent of the global population but have locked up 53 per cent of near-term vaccine supply, according to a team of researchers at Duke University’s Global Health Innovation Center. However, when the current risks that are involved with the AstraZeneca vaccine being still not fully known and understood, maybe it is for the best not to proceed any further down this path. The risk is incredibly low, but how can we ask people to take it when the results could be catastrophic?

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