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16 March 2021updated 28 Jul 2021 2:41pm

Is Europe misapplying the “precautionary principle” to the AstraZeneca vaccine?

The calculation of risk must be different during a pandemic.   

By Ido Vock

At least a dozen European governments, including Germany, France and Italy, have now suspended the use of AstraZeneca’s vaccine after reports emerged of blood clots forming in people who had received the jab.

There is so far little proof that the blood clots among people who have been vaccinated with the AstraZeneca jab is higher than among the general population. As the Cambridge scientist David Spiegelhalter writes, deep vein thromboses (DVTs) happen to about one in 1,000 people a year (and probably more among the elderly, who are more likely to have been vaccinated). We should therefore expect to see at least 100 DVTs a week among the five million or so Europeans who have received the AstraZeneca vaccine as an unrelated base rate, according to Spiegelhalter.

The European Medicines Agency, the EU’s healthcare regulator and one of the bodies so far not calling for the use of AstraZeneca to be suspended, has only found around 30 “thromboembolic events” among people who have been vaccinated. AstraZeneca said on Monday that across the EU and UK so far there have been just “15 events of DVT and 22 events of pulmonary embolism reported among those given the vaccine”.

The domino effect of successive governments temporarily halting the use of the AstraZeneca jab appears to be down to collective panic more than any scientific or epidemiological grounds.

So why have certain governments gone ahead with the suspension? A generous interpretation is that, faced with Europeans’ high levels of vaccine scepticism generally and towards AstraZeneca specifically, leaders believe they must tread cautiously if they are to achieve successful roll-outs. Appearing to be cavalier about reports of blood clots, even if anecdotal, would risk worsening suspicions and hesitancy: better to be transparent than fuel conspiracism.

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Yet some European politicians and media figures have already been careless in spreading unfounded rumours of AstraZeneca’s inefficacy, leading to a perception that it is a second-best vaccine. Knee-jerk decisions based on sparse, anecdotal evidence risk entrenching such a view.

[See also: Why are millions of doses of AstraZeneca Covid-19 vaccines lying unused in EU countries?]

The more straightforward reason for the suspension, perhaps, is simply that some governments still don’t know how to calculate risk during a pandemic.

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Most of the governments that have halted the use of AstraZeneca have cited the “precautionary principle”, a concept in some EU policy which states that precaution should prevent potentially harmful actions being taken “even before a causal link has been established by absolutely clear scientific evidence”.

The above definition uses the words of a 1987 declaration on the protection of the North Sea, and was intended to prevent potentially harmful substances being dumped even if there was no established scientific evidence proving a direct link to environmental damage.

This is an admirable principle in an environmental context, because the choice is between the status quo (the marine environment remaining as it is) and its potential degradation. In other words, there are no direct costs to waiting for more evidence.

But the calculation is different during a pandemic. Stopping vaccination is not a cost-free option, in that delay leads to deaths. One French doctor estimates that vaccinating 100,000 over-50s today rather than tomorrow saves 15 lives. As Natasha Loder, the health policy editor at the Economist put it: “This precautionary principle is a nonsense when you’re in the middle of a pandemic.”

Failure to properly understand how risk works during a pandemic explains why some governments in Europe initially didn’t approve AstraZeneca for over-65s, confusing a lack of clinical trial data about use among the elderly with ineffectiveness. It also explains why many countries are sticking to a three-week gap between doses, as was initially suggested, rather than following evidence that suggests giving more people very good protection with a single dose is a better use of scarce resources than fully protecting a smaller number of people with two.

It will now be difficult for governments to reverse the effects of the decisions made, even if, as is likely, AstraZeneca vaccinations resume. Many European citizens (and, indeed, Brits) will have heard the broad outlines of the story without learning its specifics. Many will likely be, quite understandably, more hesitant to receive the jab.

What is arguably more dangerous, though, is that this episode will fuel hesitancy in parts of the world where AstraZeneca is the only jab available. In parts of the Global South, including much of Africa, the bulk of doses likely to be available for some time will be produced by AstraZeneca (rolled out through the World Health Organisation’s Covax vaccine sharing scheme), since its jab is cheaper and easier to produce.

In Europe, it looks likely the suspensions will be overturned in the coming days when results from the EMA’s investigation into the safety of AstraZeneca’s vaccine are released on Thursday 18 March. But the saga follows Europe’s general pattern of over-cautious decision-making during the pandemic, which has left its own citizens worse off.

[See also: Could Covid-19 vaccination hinder other immunisation efforts in developing countries?]