February 12, 2021 - 11:00am

Astonishingly, about 25% of the UK adult population has now been vaccinated. That is enormous. Israel and the United Arab Emirates have done much more, but the UK is in third, well ahead of the US in fourth and miles ahead of everyone after that. (I know it’s not a race, but it’s still better to be going quickly than slowly.)

The question, of course, is: can we see the effects yet? Are lives getting saved, in numbers large enough to detect?

In Israel, the effects are dramatic. Cases, hospitalisations and deaths are all dropping; hospitalisations among the over-60s (who were vaccinated first) are now, for the first time, below those among the under-60s.

But Israel is over a month ahead of us; we’ve vaccinated about the same percentage of our population as they had on 7 January. Hospitalisations in the over-60s didn’t start to drop until 15 January.

There are other ways you can look at it. Andrew Lilico wrote an interesting blog post looking at the infection fatality rate; others have pointed out that deaths are falling faster among the elderly than among younger people, as you’d expect given that they were vaccinated first.

I spoke briefly to Professor Sir David Spiegelhalter, the Cambridge statistician, and he said you really wouldn’t expect to see any effect on someone’s risk of death for at least a month after vaccination. A month ago, we’d vaccinated less than 5% of the population. They were disproportionately among at-risk groups, but it would only be now that we’d be seeing the start of an effect. The drop in the proportion of deaths which is among the elderly is real, but it could be due to other mechanisms.

Also, it’s really hard to tease out the effects of vaccination from the effects of everything else. The rate of deaths in all age groups has been falling by about 33% a week anyway, because of lockdown. It’s much harder, says Spiegelhalter, to tell which of two things is dropping faster than it is to tell whether one is dropping at all.

(He also pointed out, interestingly, that the sort of person who’s likely to be vaccinated early in their age group is probably also the sort of person who would be careful anyway. So the effect of vaccinations might seem smaller at first than it will be on the whole.)

Deaths in the elderly might be falling faster than deaths in the younger groups because of vaccinations, although there is not, says Spiegelhalter, a corresponding fall in hospitalisations, which is odd. But at the moment, it’s a very faint signal we’re trying to detect in a very noisy environment. The good news, though, is that the signal is going to get much clearer, quickly. Fingers crossed, but I expect that in a week or so, we won’t have to do this reading-of-the-tea-leaves stuff: it’ll be very obvious, just as it was with Israel.

Tom Chivers is a science writer. His second book, How to Read Numbers, is out now.