Saved by the whistle or the bell?

Covid-19 cases are falling for the first time since the pandemic's start without there being a national lockdown. Unless there is a secret modelling team in PHE, it is fair to say most people are moderately surprised by the continued drop in reported case numbers.


The exam question is why? This drop is significant for policy decisions needed over the next few months rather than kicked into the autumn.


As with many things, there are probably several factors.


Vaccinations and natural immunity played a considerable role, but these have been gradually delivered (linearly) and, if anything, has slowed down in the last few weeks. This steady increase contrasts with doubling cases every few weeks (exponential) that we saw in mid-July. More importantly,* despite some differences in vaccination rates, case rates in England dropped simultaneously across all regions around 19th July - see chart below.

This simultaneous drop in case numbers contrasts to Scotland, where cases started dropping a few weeks earlier than in England. There are some broad alignment between these downturns, specifically (i) the country's last game in the Euros and (ii) school term dates - see chart below.

In truth, there are likely two big dynamics playing out. (We need more data to be conclusive) The first is the slow and steady increase in cases, probably driven by school mixing of a largely unvaccinated population. The second is the accelerated mixing caused by the Euros - if you look closely at the chart above, you can see a kink around mid-June (especially for Scotland). These factors driving up case numbers have now fallen away, leaving some natural immunity and reducing the overall R0. It is slightly different for hospitalisations, which are still increasing in England. There has always been a lag in admissions from infections, so we should start to see admissions numbers drop in the next week or two as we have done in Scotland. The critical policy question now is how to prepare for the autumn. There will be some more immunity from continued vaccinations and infections, but schools and businesses returning will likely lead to an increase in cases. While this will come as a nasty shock, it is likely to be the start of a seasonal pattern that COVID will start to take centered around seasonality. Perhaps the most exciting aspect of this analysis is that it suggests that both Wales and Northern Ireland supported England (or possibly just football) - see chart below!


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