COVID-19: Rapid and frequent tests could reverse the epidemic in a few weeks

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Researchers say a radical testing plan to massively favor less accurate but much faster tests than RT-PCR tests to detect as many people as possible could significantly slow the COVID-19 epidemic in just one little more than a month.

Rapid and inexpensive tests for COVID-19, especially for people who show no signs of infection, could end the pandemic in six weeks, according to a new study by researchers at the Harvard TH Chan School of Public Health and the University by Colorado Rocher. And this even if these tests are much less sensitive than clinical reference tests, such as antigenic tests that detect the antigens produced by the SARS-CoV-2 virus to determine if the person is infected at the time of the test. Like the RT-PCR (virological) test, the latter consists of a nasal sample with a swab.

But thanks to the results available in 15 to 30 minutes, these antigenic tests that also consist of a nasal sample with a swab "allow the immediate implementation of isolation measures and contact tracing," explains Assurance on the subject. Published in Science Advances, the study suggests that rapid tests, although less reliable, would allow public health authorities to rely on more specific containment interventions. "Our finding is that it is better to have a less sensitive test with results today than a more sensitive test with results tomorrow," said lead study author Professor Daniel Larremore.

The reproduction rate of the coronavirus decreases by 80%

Specifically, "instead of telling everyone to stay home to ensure that a sick person does not transmit the virus, we could give orders to stay home only to those who are contagious so that everyone can live their life," he adds. For the study, the researchers wanted to know which of the two detection factors was more important in stopping the spread of the virus: the sensitivity of the test or the response time. To do this, they analyzed the available literature on how viral load rises and falls during infection and when people tend to experience symptoms and become contagious.

They then used mathematical models to predict the impact of screening with different types of tests according to three scenarios: in 10,000 people, in a university-like setting with 20,000 people, and in a city of 8.4 million people, they found that when it comes to The reduction of propagation, frequency or response time is more important than the sensitivity of the test. For example, for a large city, generalized testing twice a week, with a rapid but less sensitive test, reduced the reproduction rate (R0) of the virus by 80% versus 58% for more PCR tests. sensitive but whose results arrive in 48 hours.

"Prioritize frequency and time period"

The reason is simple: about two-thirds of those infected have no symptoms, and while they wait for the results, they continue to spread the virus. "This article shows that we should be less concerned with test sensitivity and, in public health, prioritize frequency and response time," adds Roy Parker, director of the BioFrontiers Institute. The researchers then set out to determine to what extent focusing on frequent testing could shorten the duration of the pandemic. In their scenario, 4% of people in a city were already infected and rapid tests were performed on three out of four people every three days.

The positive cases were isolated and the results show that this protocol allowed reducing infections by 88%, a figure "enough to take the epidemic towards extinction in six weeks", estimates the scientific team. However, he admits that antigen testing requires a relatively high viral load - about 1,000 times more virus than PCR testing - to detect infection. But if the fear is to miss many positive cases of COVID-19 at the beginning of the infection for this precise reason, the researchers point out that an infected person "can go from 5,000 particles to 1 million copies of viral RNA in 18-24 hours" .

"These rapid tests are contagion tests, effective in detecting COVID-19 when people are contagious," says Michael Mina of the Harvard TH Chan School of Public Health. These tests could therefore reopen football stadiums, concert halls and airports, with people testing themselves along the way and wearing face masks as a precaution.

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