May 9, 2021

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What has really driven down cases – lockdown or the vaccine?

Analysis by Ed Conway, data editor

It’s hard to be sure with any level of precision how much one or the other intervention has made during the pandemic, but it’s pretty clear that of all the interventions during COVID-19, few have been as powerful as nationwide lockdowns. You might think this goes without saying, but even during the first lockdown there were some who argued that the fall in cases in April, May and June was less down to the lockdown than due to the behaviour of the virus itself. It had petered out, some said – simply running out of potential hosts.

Had that been correct, one wouldn’t have expected much of a resurge in the autumn. As it is, the virus returned, accelerated by the arrival of the new UK/Kent variant. In short, it’s pretty clear that what pushed down case levels in the spring was the lockdown itself.

And it’s also pretty clear from glancing at the data that the same kind of pattern seems to have happened this time around. Cases have fallen at a not dissimilar rate as they did last spring.

However, it’s also pretty clear that the vaccines have had some impact too. The best way to visualise this is via these charts. The lines simply show you the extent to which the number of new positive tests have fallen for the over-60s and under-60s. They’re rebased to the peak of the latest surge, meaning what we’re really comparing is the rate at which these levels of infection have dropped.

And if you look closely, you can see that cases for the over 60s have fallen faster than those in younger age brackets. The effects is clearer still when you look at the same lines but this time with a logarithmic axis (second chart), which depicts exponential changes more clearly. Given the over-60s are more vaccinated, it would follow that they are increasingly more protected from the virus and therefore that their case levels are falling more than for other age groups.

But here’s the key thing to note: both lines are falling. And falling fast. That is largely likely to be down to the lockdown.

So the prime minister is probably right. And a glance at other countries where there are high levels of vaccinations but fewer restrictions – for instance Chile or Hungary – might seem to provide further evidence to back up his case.