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Test and trace crucial but not enough to beat coronavirus: Study

PARIS: Testing for Covid-19 and tracing the prior contacts of those found to be infected are crucial measures for slowing the disease's spread but inadequate unless combined with other measures, researchers said yesterday.

By itself, the test-and-trace approach can reduce the virus' reproduction rate, or R number, by 26 per cent, they reported in The Lancet Infectious Diseases, using mathematical models to examine data from previously published studies.

The reproduction rate measures the number of people in a population, on average, infected by each person carrying the virus. Anything above "1" means the disease is continuing to expand; below that threshold, it will eventually peter out.

Some countries that brought the spread of Covid-19 under control but are now struggling to prevent a resurgence have R numbers well above 1.

In France, for example, it hovered at 1.33 during the first week of August, according to national health authorities.

But the new finding comes with a caveat, said lead author Nicholas Grassly, a professor at Imperial College's School of Public Health.

"Our results show that test and trace can help reduce the R number but needs to be carried out effectively and quickly to do so," he said in a statement.

That means immediate testing with the onset of symptoms and results within 24 hours; the quarantine of contacts, also within 24 hours; and the identification of 80 per cent of cases and contacts.

Very few countries - notably South Korea, Taiwan and Germany - have come close to staying within these guidelines. In France, for example, it take days to get an appointment for a test.

Even if nations do adhere to these guidelines, it will still not be enough to bring the infection rate down sufficiently by itself, the new study concluded.

"Test and trace alone won't be enough to control transmission in most communities, other measures alongside will be needed to bring the R number below 1," said Prof Grassly.

Weekly screening of high-risk groups such as health and social-care workers can reduce transmission by an additional 23 per cent, his team found. - AFP

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