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The conundrum facing vaccine regulators as they decide whether or not to restrict the use of the AstraZeneca jab is Richard Feynman’s numberplate problem. And it’s not an easy problem to solve.
Arriving at a lecture, the Nobel prizewinning physicist began with an anecdote. “You know, the most amazing thing happened to me tonight. I saw a car with the licence plate ARW 357. Can you imagine? Of all the millions of licence plates in the state, what was the chance that I would see that particular one tonight? Amazing!”
The point is that the number plate ARW 357 is indeed rare. By definition all numberplates are. And if, before heading out, he had predicted he would see that specific one, then that would have been astonishing. But he didn’t and, fairly obviously, you’re always going to see a numberplate.
In Germany 31 younger people have suffered from an extremely rare clotting disease after receiving the Oxford-AstraZeneca jab. Nine have died. On the face of it, even after 2.7 million doses, the chances of this cluster appearing are so low that it almost certainly must be due to the jab.
The problem is, though, that’s the wrong comparison. That’s like considering a single numberplate in isolation. Once a vaccine has been through trials, regulators are looking for safety concerns that could not have been picked up in trials of tens of thousands of people. These are by definition vanishingly rare.
They did not say beforehand they were worried about seeing clotting.
Instead, like Feynman looking at numberplates, they are logging every possible rare condition known to medicine.
The correct question is not, then, what are the chances of a group of vaccinated people getting this rare blood clot? It is, what are the chances of a group of vaccinated people getting any rare disease — a rare allergic reaction, a rare heart attack, a rare paralysis?
Suddenly the statistics become a lot harder to interpret, especially so when you consider the same unusual clotting levels have not been seen (either because they haven’t happened or haven’t been picked up) in the UK, a country that has vaccinated several times more people.
German regulators are not idiots. They know this. This is why a paper published last week before peer review may have been crucial in the decision yesterday to restrict the jab to older age groups.
This paper suggested a causal link between the jab and the condition. The authors, including one from the Paul Ehrlich Institute, which first raised the alarm in the country, believe it is possible that in extremely rare cases the vaccine causes a maladaptive immune response that leads the body to attack its own blood platelets.
Other scientists dispute this interpretation. Peter English, the immediate past chairman of the BMA public health medicine committee, said yesterday, “It is hard to postulate a biological reason mechanism which could explain how a clotting disorder in which clots form in a particular part of the body could be more common, when clotting, in general, is not.” It is also not clear why this particular adenovirus-vectored spike protein vaccine would cause this effect while others, such as Russia’s Sputnik vaccine, would not.
The truth is these are not decisions about the vaccine in isolation. They are about cost benefit — the vaccine may cause rare clots, the Covid-19 it prevents definitely causes clots. They are about the ethics of the individual versus the collective — do you run a small theoretical risk to vaccinate a 30-year-old nurse when the chief benefit is not to her but to those she might pass the infection on to?
Some considerations depend on the country itself. Is it better for vaccine confidence to be extra cautious and risk a scare, or to keep going and also risk a scare? And does, say, a country such as Australia, with no continuing outbreak, take a more cautious stance than one with a continuing pandemic?
There is no right answer to these questions. They are made amid extreme uncertainty. There is, though, one statistic we can be sure of. Whether caused by the vaccine or not caused by the vaccine, these tragic clotting events are vanishingly rare. Which is precisely why it’s so hard to know what to do.
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