On Monday, Canada joined several European countries in suspending use of the Oxford/AstraZeneca coronavirus vaccine in younger age groups 鈥� in Canada that means under-55s. The next day, some parts of Germany decided to do the same in people under 60. The decision follows a study out this week suggesting that a few cases of blood clots in this age group arising shortly after vaccination do seem to be caused by the jab. Should people be worried?
What are the safety fears over the Oxford/AstraZeneca covid-19 vaccine?
There have been a small number of blood clot events recorded after people have taken the Oxford/AstraZeneca vaccine across Europe, most occurring in middle-aged adults. This caused several countries to suspend the use of the vaccine in all age groups earlier this month. A review by the European Medicines Agency (EMA) said the vaccine was safe to use, and vaccine roll-out resumed in most countries. But France, Sweden, Finland and Iceland have restricted its use to people over a certain age, ranging from 55 and over to 70 and over, depending on the country.
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Why, if it was deemed safe?
In March, the EMA鈥檚 safety committee reviewed data on the vaccine. Overall, the number of blood clotting events reported after vaccination, both in studies before licensing and in reports after roll-out of vaccination campaigns, was lower than you might expect to find in an unvaccinated general population. So the committee concluded that the vaccine isn鈥檛 linked with a raised risk of blood clots overall.
However, the EMA found that, in younger people, the vaccine may be associated with very rare cases of blood clots coupled with low levels of platelets, including a rare type of clot in vessels draining blood from the brain, called cerebral venous sinus thrombosis (CVST).
How many blood clotting events have there been since the roll-outs began?
About 20 million people in the UK and European Economic Area (EEA) had received the vaccine as of 16 March. At this time, the EMA had found 25 cases of unusual blood clots within this population, which included 18 cases of CVST. These figures are likely to have increased by now. Yesterday, Germany鈥檚 medical regulator said it had identified 31 cases of CVST in the country.
So what is the latest news?
Now, Andreas Greinacher at Greifswald Medical School in Germany and his colleagues say that occur after receiving the Oxford/AstraZeneca vaccine. In a preprint published this week, the group calls this process vaccine-induced prothrombotic immune thrombocytopenia (VIPIT). On Monday, Canada suspended use of this vaccine in under-55s , and now some parts of Germany have suspended roll-out to those under 60.
What has the new study found exactly?
The team investigated nine vaccine recipients who subsequently had , and did blood tests on four of them. The team found that all four had signs of a normally very rare low-platelet syndrome that is usually caused by a reaction to heparin, a blood-thinning treatment, although it can have other triggers. The team says this suggests the vaccine directly caused the blood clot syndrome. 快猫短视频 contacted AstraZeneca for comment but didn鈥檛 hear back before this article was published.
Could there be other explanations?聽
This is a small study that has limitations. For instance, it doesn鈥檛 compare the number of people with this rare syndrome with the background rate in unvaccinated people, said Adam Finn at the University of Bristol, UK, in a statement. Two of the nine cases had a pre-existing blood clotting disorder and it isn鈥檛 stated whether any of the group had recently had covid-19, which can cause an increased risk of blood clots.
In general, some clots attributed to the vaccine could be caused by a natural infection, says Leonard Yeo at the National University Hospital of Singapore, who described a of CVST caused by covid-19 last year in people who hadn鈥檛 been vaccinated. Two of these people had none of the typical covid-19 symptoms, like coughing or fever.
Another issue is that most cases identified by the EMA occurred in women under the age of 55, a group that has a higher rate of blood clots, including CVST, because taking the contraceptive pill raises the risk. Perhaps some CVST cases being attributed to the vaccine are simply the usual background rates, says Beverley Hunt, medical director of Thrombosis UK. But Hunt, who is working with the UK鈥檚 Medicines and Healthcare Products Regulatory Agency (MHRA) to assess the risk, says CVST isn鈥檛 normally seen with low platelet counts, which suggests that something unusual is happening in these rare cases.
How dangerous are the blood clotting events?
They can be deadly. In the new study, four out of the nine people affected have died and one was still in hospital when the preprint was published online this week.
What conclusions should we draw?聽
The number of possible cases of blood clots associated with the vaccine are so small that the EMA, the MHRA and the World Health Organization are still saying that the benefits of having the jab outweigh any risks.
鈥淥ur advice remains that the benefits of the AstraZeneca vaccine in preventing covid-19 infection and its complications continue to outweigh any risks and you should continue to get the vaccine when invited to do so,鈥� says June Raine, CEO at the MHRA.
What happens next?聽
The EMA and MHRA are continuing to investigate the reported cases of blood clots. It is possible that further countries will restrict use of the vaccine in lower age groups as a precautionary measure, says Hunt. 鈥淓veryone is working flat out on this.鈥�
