Weighing up the ultimate costs & benefits of lockdown measures is a challenge

In March 2021, a doctor in Brazil named Ricardo Savaris published a now-discredited research paper that went viral on social media1.

It had been a year since the first wave of the COVID-19 pandemic forced governments to apply the desperate measures collectively known as lockdowns — cancelling sporting and cultural events, closing retail outlets, restaurants, schools and universities, and ordering people to stay at home. At the time, countries were once again dialling lockdown policies up or down, as the Alpha variant of the coronavirus SARS-CoV-2 surged in different places.

Lockdown measures did what they were supposed to. When they were enforced rigorously enough to reduce people’s social contacts sharply, they shrank COVID-19 outbreaks; several studies had demonstrated this.

But Savaris, an obstetrician and gynaecologist at the Federal University of Rio Grande do Sul in Porto Alegre, tried a fresh analysis together with three colleagues (who worked in statistics, computer science and informatics). They compared 87 locations around the world, in pairs, to see whether a lower rate of COVID-19 deaths correlated with greater time spent at home, assessed using anonymized cellphone data released by Google. In most cases, their paper in Scientific Reports concluded, it didn’t.

The paper was highlighted by prominent lockdown sceptics and some news sites and swiftly gained notoriety. “The findings were quite remarkable, on the face of it,” says Gideon Meyerowitz-Katz, an epidemiologist at the University of Wollongong, Australia. As he and others would show, the results were wrong, because of errors in the paper’s choice of statistical methods.

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