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Can we be sure Covid-19 cases are falling?

The latest data from Scotland gives us reason to be cautiously optimistic that the current wave has peaked.

By Stuart Ritchie

Remember back at the start of 2020, when other countries, like Italy, were “a couple of weeks ahead” of the UK in their Covid-19 epidemics? Despite this being repeated over and over in the press, we didn’t do much about it, but at least we were forewarned.

Now, amid our third Covid wave driven by the newer Delta variant of the coronavirus, there are more tidings from the future – but unlike the warnings from early in the pandemic, they might constitute very good news.

As an Edinburgh native, I’m happy to report that the encouraging data from the future come from Scotland, which is ahead of the UK as a whole in its third wave. Scotland’s coronavirus cases peaked in the first days of July and have been in precipitous decline ever since. For many Covid hawks and worriers, it looked too good to be true: could this be some kind of statistical artefact or aberration? Could the numbers be due to differences in testing or to some other explanation that didn’t really mean fewer people were infected with the virus?

Today, we saw the latest evidence from the Office for National Statistics infection survey, which helps answer those questions.

The survey asks a random sample of households to send in nose and throat swabs for testing (this is how we get weekly information about the number of people in the country being infected with Covid). The random part is crucial: it’s not a matter of self-selection, where some people might go out of their way to get – or to avoid – a test, skewing the numbers one way or another. The ONS survey numbers can thus be used to confirm or contradict the general testing figures which we have concentrated on in the past weeks.

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Of course, because data take a while to analyse and release, the ONS survey is a tad behind. There’s a lag of about a week – and that’s the key here. Given that Scottish rates have been declining for a while, the lag means that the ONS survey data can be compared to the decline. The decline elsewhere in the UK is too recent for the ONS data to be able to confirm the trend.

[see also: The fall in UK Covid-19 cases isn’t due to less testing]

What does the ONS data tell us about the current situation in Scotland? For the first time in the current wave, it confirms that rates in Scotland have declined. In the week up to the 17 July, 1 in 80 people in Scotland were infected; up to 24 July, that number stood at 1 in 110. 

That’s very exciting news, because we’ve seen those testing numbers – with a few blips here and there – decline in England and Wales too (the rates in Northern Ireland seem to have peaked but don’t show a decline).

The other positive news from Scotland, as the Economist’s Mike Bird has pointed out, is that hospitalisations are going the same way as cases: downwards. If cases really are declining, it would be bizarre to see hospitalisations stay static or increase; that they’re on the way down is another piece of evidence that the general decline is real.

The question is: why? Why would there have been a spike in rates followed by a sudden decline?

It’s probably silly to speculate at this point: all sorts of survey, mobility and other data will have to be analysed carefully to work out what happened. Did the Euros, with everyone crowding into pubs and living rooms to watch the football, cause the spike in recent weeks? Some age trends suggest that might be so. Could the decline be due to the weather? I’m told it’s been very much “taps aff” weather in Scotland during July, so more people are outside and are thus more protected from the virus. Could it be schools? The summer holidays begin earlier in Scotland than in the rest of the UK – though perhaps not early enough to explain the decline in rates from the very start of July.

Equally importantly, could things rapidly get worse again? Absolutely. It’s possible that we’ll soon see cases increase due to the full reopening in England on 19 July. The decision from the Joint Committee on Vaccination and Immunisation to vaccinate only extremely clinically vulnerable children from age 12 to 18 – and to prohibit parents of other under-18s to decide with their kids whether or not to get them jabbed – means that we’ll struggle to reach full herd immunity, and there’ll be an increased risk of more outbreaks in schools when pupils return.

But it’s nice to take a moment to focus on the good news. The ONS survey – a lovely example, by the way, of the different UK nations working together to produce comparable data – should make us (cautiously) optimistic. The critical thing now is to work out what’s causing the decline – and act on it.