27 September 2021

Nature: “Why many countries failed at COVID contact-tracing — but some got it right”

The WHO’s benchmark for a successful COVID-19 contact-tracing operation is to trace and quarantine 80% of close contacts within 3 days of a case being confirmed — a goal few countries achieve.

But even that’s not quick enough, says Christophe Fraser, a mathematical biologist at the University of Oxford, UK. Transmission is too rapid and the virus can spread before symptoms emerge, he points out. Modelling by Fraser and his team suggests that even if all cases isolate and all contacts are found and quarantined within three days, the epidemic will continue to grow. He says that in a single day, 70% of cases need to isolate and 70% of contacts need to be traced and quarantined for the outbreak to slow (defined as each infected person passing the virus to fewer than one other, on average)6.

At the beginning of the pandemic, overstretched contact-tracers in the United States, Australia and the United Kingdom faced the extra burden of antiquated health-care systems. In Australia, as well as in US states such as Hawaii and Washington, health departments are often notified of new cases by fax or phone. It’s somewhat embarrassing, says Plescia, but we never invested in the systems to allow them to do it differently. Entering names and other details into a database from faxed notifications causes big delays, he says, so that the window during which contact-tracing might make a difference vanishes.

Dyani Lewis

Interesting analysis that goes through several reasons for the low effectiveness of contact tracing in many countries. Paradoxically, while the lack of modern digital technology can hinder contact tracing efforts, advanced technological solutions, such as the decentralized contact tracing protocol introduced early in the pandemic by Apple and Google, have also failed to live up to expectations. Low adoption aside, a decentralized system relies on individual initiative by entering positive test results in the app and isolating – a high ask for many people, as we have all discovered – but even worse it withholds data from health authorities, who cannot make proper projections and estimations of the extent of infection.

An Israeli soldier in a call centre in Ramla talks on the phone to a person infected with coronavirus to try to identify their contacts
An Israeli soldier in a call centre in Ramla talks to a person infected with coronavirus to try to identify their contacts. Credit: Sebastian Scheiner/AP/Shutterstock

I wonder if the widespread availability of rapid tests has a similar adverse effect: people can self-test easily at home, but as long as their symptoms are mild, they are under no obligation to report their positive result to authorities (as far as I know at least). Thus the number of active cases is miscounted, and authorities are too slow to react because they do not have a realistic idea of the size of the outbreak.

There are naturally examples of positive uses of data and algorithms as well, such as this report about how Greece used machine-learning to determine which travelers entering the country should be tested for COVID-19.

But a defining factor in this crisis remains political leadership, specifically the willingness to act quickly and decisively, even before scientists can form proper recommendations, and a high level of trust in the government, as illustrated by the contrast between Denmark and Sweden:

Prime Minister Mette Frederiksen’s justification left little to interpretation: If we have to wait for evidence-based knowledge in relation to the coronavirus, we will quite simply come too late. The Danish approach involved the imposition of restrictions and the expansion of state authority in ways more reminiscent of places like Taiwan or Singapore that helped flatten the curve of the contagion by means of mass surveillance, contact tracing and stringent quarantine enforcements.

In contrast, Sweden’s approach could easily be mistaken for the populist denialism of Jair Bolsonaro in Brazil or Donald Trump in the U.S. While it enacted a number of targeted closures, such as schools for over-16s, the government in Stockholm deliberately left social life to proceed as normally as possible. Following a mostly volunteer-based approach, the Swedish Prime Minister Stefan Löfven declared: We who are adults need to be exactly that: adults. Not spread panic or rumors. No one is alone in this crisis, but each person carries a heavy responsibility.

Fabrizio Tassinari

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