Deciding when to suspend a vaccine
More or Less
BBC
4.6 • 3.7K Ratings
🗓️ 20 March 2021
⏱️ 9 minutes
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Summary
Many countries recently decided to suspend the use of the AstraZeneca coronavirus vaccine over fears it was increasing the risk of blood clots. The European Medicines Agency and the WHO called on countries to continue using the vaccine but regulators in individual countries opted to be cautious, waiting for investigations to take place. But why?
Tim Harford explores the risks of blood clots and weighing up whether it was necessary to suspend using the vaccine.
Transcript
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| 0:00.0 | Hello and welcome to More or Less on the BBC World Service, |
| 0:03.8 | with a programme that explores the numbers in the news and in life, and I'm Tim Halford. |
| 0:09.2 | This week we're looking at the decision made by a number of countries to suspend the use of |
| 0:13.7 | the AstraZeneca coronavirus vaccine. Back on March 11, Denmark became the first country to suspend |
| 0:20.8 | all AstraZeneca vaccinations for two weeks after a 60-year-old woman had been vaccinated, |
| 0:26.6 | formed a blood clot and died. More cases emerged and more countries followed suit, Austria, |
| 0:32.7 | Norway, followed by Germany, Italy, France and a number of others both in and outside Europe. |
| 0:39.0 | But while the regulatory bodies in these countries decided to suspend the use of the vaccine, |
| 0:44.0 | the European Medicines Agency and the World Health Organization encouraged the continued use of |
| 0:49.1 | the vaccine. So what was going on? Professor Jennifer Dowd is Deputy Director of the Leaver |
| 0:55.4 | Hume Centre for Demographic Science at the University of Oxford. She's also a contributor to |
| 1:00.8 | Dear Pandemic, a COVID-19 science communication platform. Serious blood clotting events, including |
| 1:08.1 | deep vein thrombosis or pulmonary embolisms are actually not that uncommon, unfortunately. |
| 1:15.0 | They happen with an estimated annual incidence of about one per thousand in the adult population. |
| 1:21.0 | And so at that rate, if five million adults are vaccinated in one week, we would expect roughly |
| 1:28.4 | 95 of those to have a clotting event even in the absence of the vaccination. And so, according to |
| 1:36.0 | the European Medicines Association, as of March 10, there were 30 cases of these clotting events |
| 1:42.1 | reported in the five million people given the AstraZeneca vaccine. So in fact, it's actually |
| 1:47.9 | lower than what one would expect from baseline rates. I suppose the problem here is that for an |
| 1:54.3 | individual, now I do not expect to have a blood clot. I certainly don't expect to be killed by |
| 2:00.8 | a blood clot. And I don't often get vaccinated. So from the point of view of an individual, |
| 2:06.2 | if I get vaccinated in a week later, I have some serious medical event, a blood clot that threatens |
... |
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