Google mobility index

How Much Did Lockdown Affect U.K. Mobility?

The mainstream narrative concerning England’s national lockdowns is that each one arrested a steep upward trend in daily infections that would have otherwise continued unabated. Infections were rising; we had a lockdown; and infections started falling.

However, there are several reasons to doubt this narrative. To begin with, the international evidence suggests the impact of lockdowns on COVID-19 outcomes was marginal at best. They only ‘worked’ – in the sense of halting a nascent epidemic – in a small number of geographically peripheral Western countries, like Australia and New Zealand.

Next, the statistician Simon Wood crunched the numbers on the three English lockdowns, and found that infections were already declining before each one was introduced. His analysis is consistent with the time-course of infections reconstructed by researchers on the REACT antibody survey.

What’s more, the economist David Paton identified seven separate indicators, each showing that infections peaked before the third English lockdown. Indeed, lockdowns are often imposed around the peak of the curve, as governments come under increasing pressure to ‘do something’ about rising case numbers. (Back in July, Chris Whitty told MPs the epidemic was probably already in retreat when the first full lockdown was imposed.)   

The way lockdowns are assumed to work is by reducing the number of interactions that result in viral transmission. However, distinguishing their impact from that of voluntary changes in behaviour is no easy feat (see my recent interview with Philippe Lemoine).

What’s more, since transmission is driven by ‘superspreaders’ (those few individuals who account for a disproportionate share of infections), the relationship between interactions and infections isn’t necessarily linear. For example, reducing interactions by 50% may reduce infections by much less than 50%.

Rather than trying to tease out the effect of lockdowns on infections, one can look at their impact on mobility. If lockdowns are what account for the curves peaking and then falling, one would expect to see sudden declines in mobility just after lockdowns are introduced. And you’d expect these declines to be sustained until case numbers had come down substantially.

Is that what we see? We know from the Google mobility index that there was a rapid decline in mobility during March of 2020, though that decline began seven to 10 days before the first lockdown commenced (on March 24th). This is shown in the chart below:

Google Mobility Data Suggest That ‘Freedom Day’ Will Not Cause a Rebound in Cases

New daily infections have fallen by 31% over the last seven days, causing some consternation and head-scratching in the epidemiological modelling community.

Neil Ferguson, for example, had claimed only ten days ago that cases reaching 100,000 per day was “almost inevitable”. Yesterday he backtracked, noting that “the equation has fundamentally changed”. (One hopes he was referring to the equations in his model.)

As to why daily infections have been falling, some epidemiologists have said the full effects of ‘Freedom Day’ are yet to appear in the data. ‘Freedom Day’, you will recall, was when some remaining lockdown measures were lifted on the 19th of July.

Yesterday, the Prime Minister told reporters, “Step Four of the opening-up only took place a few days ago, people have got to remain very cautious and that remains the approach of the Government.”

Aside from the fact that ‘Freedom Day’ was nine days ago, and you’d expect any effects to show up by now, there’s another indicator suggesting that a rebound in cases is unlikely – the Google mobility index.

Google publishes regular reports on the level of mobility in most of the world’s countries, based on smartphone data. Looking at the latest U.K. numbers, there is no evidence of any change in behaviour caused by ‘Freedom Day’.

The chart below shows the retail mobility index. (Numbers are percentage changes relative to the baseline; ‘Freedom Day’ is marked with a red line.) As you can see, there was no sudden increase on the 19th of July.

The next chart the residential mobility index. Once again, there was no sudden decrease on the 19th of July. (And the other four sub-indices show the same pattern.)

Of course, the Google mobility index isn’t a perfect guide to behaviour. And given that rapid decreases in case numbers have occurred in the absence of mobility changes, it’s possible that rapid increases could too. Nonetheless, these figures suggest that daily infections aren’t about to rebound, and we don’t need to “remain very cautious”.