In mid-March, a number of European countries suspended their use of the AstraZeneca (AZ) Covid-19 vaccine following reports of blood clots in a small number of people who got the jab.
The European Medicines Agency (EMA) concluded that the vaccine was ‘safe and effective’ after an investigation into the possible link, and Phase III data published by AZ shortly afterwards claimed that there was no causal link between the jaw of the enterprise is not and that blood clotting events have been reported at some recipients. .
Now, less than a month later, both the EMA and the UK Medicines and Healthcare Products Regulatory Agency (MHRA) have published reports confirming evidence of a possible link between AZ’s jab, now known as Vaxzevria, and ‘extremely rare’ cases of blood clots. The EMA’s safety committee noted that the reported blood clots were found in the brain, abdomen and arteries, and that it was related to thrombocytopenia or low platelet counts. Both regulators said the benefits of the vaccine outweigh the potential risks, and that people still need to be vaccinated when asked.
The EMA is also investigating a possible link between Vaxzevria and five cases of capillary leak syndrome, a rare disease characterized by fluid from the blood vessels, causing tissue swelling and a drop in blood pressure. The agency said no causal link had been established at this stage.
Of the 79 British blood clotting cases after a first dose of AZ vaccine reported by the end of March, 19 people died. The MHRA said 11 of these people were under the age of 50 and three were under 30.
Amid concerns about the safety of the vaccine among younger recipients, a number of European countries have now restricted its use to older age groups. Although the MHRA does not recommend an age restriction for the jab in its updated guidance, the UK Joint Committee on Vaccination and Immunization (JCVI) has recommended that young people under 30 should be given an alternative vaccine, where possible – so how concerned should we be be?
Vaxzevria and blood clots: the risk in context
In the UK, more than 20 million doses of AZ vaccine have been given so far. According to the MHRA, the risk of a serious blood clot due to the jab is about one in every 250,000 people vaccinated, or four in a million. It is also noteworthy that Covid-19 itself poses a significant risk for blood clots; according to a study in the journal Thorax, the incidence of pulmonary embolism and thrombosis in deep veins in people with the virus was 7.8% and 11.2%, respectively.
In addition, around 10,000 people usually develop blood clots in the EU in a given month, while an estimated 3,000 blood clots occur each month in the UK. The general population’s risk of cerebral venous sinus thrombosis (CVST) – one of the blood clot types observed in Vaxzevria recipients – is about five out of a million; slightly higher than the risk associated with the vaccine.
Emeritus Professor of Applied Statistics at the Open University, Prof Kevin McConway, said: ‘One thing that needs to be done to find out if a possible adverse effect is caused by the vaccine is to compare how often the effect after vaccination has taken place, compared to the vaccine. to how often it occurs in healthy, vaccinated people.
‘Just to show how difficult it can be, a recent EMA report on blood clots looked at the background risk of CVST, one of the most serious blood clotting disorders being considered. They say that in a million people who are followed up for a year (before Covid), somewhere between two and five may have a CVST, but point out that more recent studies say it could be 13 or 16 cases, not two or five, and that it appears to be because data is collected more carefully.
“With this uncertainty about what would happen without Covid and without vaccination, it is difficult for the regulatory authorities to make the comparisons they have to make. And if they do, there could still be great uncertainty, as said. ”
It has also been widely reported that the risk of blood clots for those taking the contraceptive pill is about one in 2000 – significantly higher than the risk for people receiving the AZ vaccine, but cases are still so rare that there are no restrictions on the prescription has not been posted. the pill for healthy people.
The occurrence of severe blood clots due to:
The contraceptive pill: 0.6%
The AZ vaccine: 0.00017%
How much time did you spend brainwashing over the first one?
I really hope the media is proportionate in their reporting.
– Keir Shiels (@keirshiels) 7 April 2021
AZ’s jab is not the only one being investigated for possible side effects; the U.S. National Institutes of Health has begun a Phase II clinical trial examining the Moderna and Pfizer Covid-19 vaccines, following reports of rare but severe allergic reactions in some who got the jabs.
As of Friday, the EMA has also begun investigating reports of blood clot events in people who received the coronavirus vaccine from Johnson & Johnson (J&J). Four severe cases of low blood platelet counts were reported after vaccination with the J&J jab, one of which was fatal. The agency said it was “currently unclear” whether there was a link between the vaccine and these events.
Cause versus Coincidence
The novelty of Covid-19 vaccines, and thus the relatively scarce data, means that the distinction between correlation and cause when it comes to the AZ jab and blood clots will be.
While regulators in the UK and EU have concluded that blood clots are a possible – albeit extremely rare – jab side effect, no agency has confirmed a causal link. The EMA said that most severe cases of blood clots occurred in women under the age of 60, but both regulators said there were currently no risk factors. One possible explanation for women who make up the majority of cases is that many of the first people to receive vaccinations were health workers, most of whom are women.
The EMA did suggest that the combination of blood clots and low platelets could be caused by an immune response similar to treparositis caused by heparin, a reaction sometimes seen in those treated with the blood thinner heparin. The agency’s pharmacovigilance risk assessment committee has requested new studies and amendments to the ongoing investigations to provide more information.
The restriction of Vaxzevria to older populations in EU countries, and the JCVI’s recommendation to offer alternative vaccines under the age of 30, are not the result of any specific conclusions about a causal link between the vaccine and blood clotting events. , or fixed age-related risk factors.
Although it can be argued, these limitations are an excessive correction of the perception of the risk of the vaccine, but in many ways it is a rational response to the risk-benefit balance of the AZ survey to people in their twenties. which are much less likely to be admitted to intensive care if they contract Covid-19 than their older counterparts. As British Deputy Chief of Staff Jonathan Van-Tam acknowledged in a press release on April 7, this means that the risk of side effects may outweigh the benefits of vaccination in younger people, especially in a scenario with ‘ a low exposure.
‘If you look at the 20-29 age group, the potential benefits are [of vaccination] ”was 0.8 ICU admissions averted, compared to serious damage of potentially 1.1,” Van-Tam said.
Expert perspectives
The World Health Organization (WHO), in addition to urging the UK and EU health authorities to continue vaccinating people, said in a newsletter that the benefits of the AZ jab outweigh the risk of rare side effects.
WHO Director-General Tedros Adhanom Ghebreyesus said that although more research was needed, “the risks of serious illness and death from Covid-19 are many times higher than the very small risks associated with the vaccine.”
Dr. Simon Clarke, associate professor of cellular microbiology at the University of Reading, said potential risks should be investigated, but people should not hesitate to take a second dose of AZ’s ‘safe and effective vaccine’.
“The fact is that all vaccines pose risks,” he said. ‘It is good that all emerging risks are further investigated, but it must be balanced against the risks of not being vaccinated. I would love to have an AstraZeneca jab, and although I will pay more attention to the symptoms of blood clots, I would gladly take the 250,000 chance of developing a blood clot, compared to no protection against Covid-19 not. ‘
European confidence in AZ vaccine declines
Although transparency and proactive monitoring around the risks of the AZ vaccine and others are invaluable to the safety of the public during this unprecedented global vaccination campaign, it is also becoming increasingly clear that the ongoing assessment of the Vaxzevria blood clot risk is a hesitation in the vaccine causes.
UGov poll data from late March showed that although UK citizens have relative confidence in the safety of the AZ vaccine – 77% of respondents believe it is safe, a 4% drop from February – confidence in the mainland dropped. In Germany, only 32% of respondents thought the jab was safe, a 11% drop from the previous YouGov poll, while countries that previously had a strong majority in Italy and Spain trusted in the safety of the vaccine, the part of those who believe in the safety of the vaccine. decreased to 36% and 38% respectively.
To properly understand the risks associated with vaccination, it is important to acknowledge its benefits as well. The AZ jab has been shown to provide almost total protection against serious diseases and death due to Covid-19, and it can also be experienced by those who have the virus against the blood clots. According to Public Health England, Covid-19 vaccines have prevented 10,400 deaths in those aged 60 and over in the UK – and because the coronavirus pandemic has so far claimed more than three million lives worldwide, it is probably worth it was worth taking. During this important time, it is up to individual governments and health institutions to consider and act on these complex risk benefit data in the context of their own population.