Concerns over the AstraZeneca vaccine

The vaccine was suspended in several EU countries, but why?
23 March 2021

Interview with 

David Spiegelhalter, Cambridge University


Covid vaccine vials


A suspected link to the development of a rare syndrome involving the formation of blood clots in the brain's blood vessels led to 18 European countries temporarily halting their use of AstraZeneca's COVID-19 vaccine pending an investigation by the EMA, the European Medicines Agency. The EMA itself though, while it investigates, is urging EU nations to continue to use the vaccine, which has so far been administered to over 17 million people, owing to the very real threat posed by massive surges in COVID-19 cases across Europe. That said, some countries, like Belgium and the UK, elected not to interrupt their vaccine rollouts. In the end, it all comes down to balancing risk: the risk from a very rare, and possibly unconnected medical condition, versus the relatively much bigger risk of succumbing to COVID-19 infection and its other sequelae. Chris Smith spoke to Cambridge University's David Spiegelhalter Professor on the Public Understanding of Risk, to get a handle on what's going on...

David - I think it’s quite complicated, because the story as it was last week, was about blood clots, like deep vein thrombosis and other things. And I looked at that data, what was being reported by AstraZeneca in terms of the number of adverse reactions. They didn’t look like anything special at all, but it’s since come out that real concern is, from both  Norway and Germany in particular, is a particular special form of thromboses, known as cerebral sinus venous thrombosis, and it’s associated as well with low platelets. So it’s clearly quite a rare syndrome, and in Germany in particular, they’ve had 1.6 million vaccines, and have had 6 or 7 cases of something like this, and it tends to be in younger women, and some have died. And so I can understand that there is a concern about the AstraZeneca vaccine.

Chris - But policy makers have to make decisions all the time, don’t they, about what you’re going to do and what the cost might be? And what you’re not going to do, and what the cost might be, and it is really important not to chuck the baby out with the biological bathwater, because by deferring vaccination while you investigate a very remote risk of something happening, you end up costing people the chance to be vaccinated in the interim. One commentator in France pointed out that for every 100,000 people you don’t vaccinate over the age of 50 for one day, that will translate into 5 deaths, I haven’t checked that statistic, but it does sound plausible.

David - Certainly, any delay will translate into deaths, especially as the continent has seen an increase in cases every day. And so, this is a really precarious situation they're in with a very low vaccination rate. And in that context, the cautious approach that the regulatory agencies are taking by suspending the vaccine while they investigate, quite reasonably, doesn't seem to me and many others, that this is the cautious approach. Actually, the default should be to try to get as many jabs as possible into people's arms, knowing that will save lives, rather than stopping the roll out, possibly decreasing even more vaccine acceptance by the population, who are already slightly skeptical because of the possible small risk of an adverse effect.

Chris - So statistically speaking, how should they investigate something like this, you're advocating that they should carry on business as usual, but behind the scenes, obviously be taking this seriously. That's how we have a healthy pharmaceutical industry, let's face it, but what should they be doing in order to work out whether or not there is a genuine effect?

David - This is what the European medicines agencies will be doing at the moment, they'll be collecting data on adverse events, which are reported, publicly reported, in the UK. And, because we've had three of those particular conditions under the AstraZeneca vaccine, one under Pfizer so far. So they'll be collecting those and looking at them, you know, whether they cluster by a particular age, or sex of people, but also comparing it with how many we would have expected anyway. That's the crucial thing, nasty things happen. People do get blood clots. And so how many would we expect anyway, and is what we're observing way above what we would normally expect to happen just by bad luck.

Chris - But as Stephen Evans, who's professor of biometry at the London school of hygiene and tropical medicine has pointed out, if you look at people with COVID, 30% of the time, they have changes to their clotting.

David - Well, I mean, that's the whole issue, cost and benefits of the two actions. Certainly by not vaccinating people, you are exposing them to considerable harm, including the risk of blood clots.

Chris - You raised an important and interesting point when you said there's also Pfizer's vaccine, and we've had cases of this there. Are they broadly comparable in terms of when you see these side effects, are we seeing roughly the same number of these adverse events in both vaccines? Therefore, again, arguing that this is not a vaccine specific effect, it's perhaps just a consequence of having a vaccine.

David - They haven't got enough data to show that, but one of the concerns there's been is about low platelets thrombocytopenia, that's been observed or linked to the Pfizer and the Moderna vaccine as well in the States. Again, the causal link hasn't been proved, but we still can't say whether this is a vaccine effect, I think, or a product effect. This is what EMA will be looking at very carefully, indeed.


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