Blood clot fears and the AstraZeneca vaccine: what we know
No evidence of a link but several European countries have suspended the shot
“In the UK, about 165 people a day might suffer a thrombotic episode, some of which will be fatal,” Ward said. “In contrast, the number of reports from the ongoing vaccine programme in the UK and EU, which includes [more than] 20 million individuals vaccinated to date, is just 37. By chance alone at least 15,000 such events might have been expected from a population of that size.”Since receiving emergency approval in the UK and EU, the vaccine has been administered to millions of people. The UK’s yellow card safety monitoring system has found that their overall safety profile is no different to what was seen in the clinical trial, and the number of suspected adverse reactions are at a similar level to other routine vaccines.
There's no proof the Oxford vaccine causes blood clots. So why are people worried?
Call it luck, chance or fate – it’s difficult to incorporate this into our thinking. So when the European Medicines Agency says there have been 30 “thromboembolic events” after around 5m vaccinations, the crucial question to ask is: how many would be expected anyway, in the normal run of things?
We can try a quick back-of-the-envelope calculation. Deep vein thromboses (DVTs) happen to around one person per 1,000 each year, and probably more in the older population being vaccinated. Working on the basis of these figures, out of 5 million people getting vaccinated, we would expect significantly more than 5,000 DVTs a year, or at least 100 every week. So it is not at all surprising that there have been 30 reports.
So far, these vaccines have shown themselves to be extraordinarily safe. In fact, it’s perhaps surprising that we haven’t heard more stories of adverse effects.
"More than 11 million doses of the AZ vaccine have now been administered across the UK, and the number of blood clots reported after having the vaccine is not greater than the number that would have occurred naturally in the vaccinated population.
Covid vaccinations: No reason to stop using AstraZeneca jab, says WHO
On Friday, AstraZeneca said the recorded number of blood clots in vaccinated people was "significantly lower... than would be expected among the general population".
COVID-19: Blood clots and the Oxford-AstraZeneca coronavirus vaccine - what does the data say?
Overwhelming opinion among British scientists is that there is no certain link between blood clots and the Oxford-AstraZeneca jab.
Monday 15 March 2021 23:51, UK
Regardless of vaccination, blood clots are fairly common - and given the sheer number of people who are getting a jab, these incidents could be coincidental.Professor Stephen Evans of the London School of Hygiene and Tropical Medicine said: "The problem with spontaneous reports of suspected adverse reactions to a vaccine are the enormous difficulty of distinguishing a causal effect from a coincidence.
"This is especially true when we know that COVID-19 disease is very strongly associated with blood clotting and there have been hundreds if not many thousands of deaths caused by blood clotting as a result of COVID-19 disease.
An Oxford University spokesperson said: "Thromboembolic disease - not related to vaccines - is reasonably common in the UK general population, occurring in one in every 1,000 people.
The UK Medicines and Healthcare products Regulatory Agency (MHRA) are monitoring these and have indicated that they are not seeing an increase from this baseline level as part of the vaccine rollout, which reassures us that it is unlikely to be a problem, which is supported by further data from the Finnish health authorities."
治験段階でも現実のワクチン接種の段階でも、ワクチン射って血栓発生数が増えたということはない、と。
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