How circuit breaker helps to prevent spread of coronavirus

Aim is to bring down the average number of people who catch it from a single infected person

An exercise station in Pasir Ris being cordoned off as part of stricter social distancing measures. These measures would be deemed a resounding success if the number of daily cases falls to the single-digit zone by May 4, when the circuit-breaker pha
An exercise station in Pasir Ris being cordoned off as part of stricter social distancing measures. These measures would be deemed a resounding success if the number of daily cases falls to the single-digit zone by May 4, when the circuit-breaker phase ends, said Associate Professor Alex Cook. ST PHOTO: KEVIN LIM

Singapore swung into full circuit-breaker mode yesterday, with schools closing as students moved to home-based learning a day after most workplaces in Singapore were shuttered.

The aim? To contain the outbreak of Covid-19, or in statistical terms, to drive down R0 (pronounced R-naught).

R0 refers to the basic reproduction number of a disease. It provides healthcare officials with a gauge of the average number of people who will catch the disease from a single infected person.

Globally, the R0 for Covid-19 is estimated to be between two and three. This means that on average, every Covid-19 patient will go on to infect about two to three others.

But this number is not a static one.

It depends on a range of factors, including biological factors, such as how easily the virus is transmitted, and social ones, such as the number of people an infected person is exposed to.

The National Centre for Infectious Diseases said it has no ongoing studies to determine the R0 for Singapore.

But Associate Professor Alex Cook, vice-dean of research at the National University of Singapore's Saw Swee Hock School of Public Health, said data suggests that Singapore's cumulative measures to contain the outbreak have been successful in driving down R0 for the disease to be at or below one since the start of the outbreak in January.

This means that each infected person here spread the disease to about one other person, on average.

While this may seem surprising given the growing number of daily cases, many of these were likely to have been infected by people who had caught the virus overseas, where the full-blown epidemics took place, said Prof Cook, an expert in infectious-disease modelling.

If R0 had been as high as two to three here, as it was in many of the worst-hit places, then Singapore would have had substantially more cases, said Prof Cook.

He said Singapore might be able to control the outbreak if the nation shuts its borders fully. "But these are big demands. We can't turn returning nationals away, and to keep contact tracing going is exhausting." That is why the circuit breaker measures are so important.

Prof Cook said: "If everyone adheres to the social distancing, we should see the number of cases drop to a more manageable level over the next few weeks."

Tackling the outbreak of an infectious disease - especially one caused by a virus that no one has seen before - is a challenging task requiring all hands on deck.

Scientists around the world are scrutinising the basic biology of Sars-CoV-2, the virus that causes Covid-19, to see how the disease can be best treated with anti-viral medication or prevented with a vaccine.

But as that work goes on, it is also important to ensure social distancing measures are in place, said Prof Cook, as this will prevent the number of cases from surging until it overwhelms the healthcare system.

R0 indicates the transmissibility of the disease in the absence of control, he said. "It is difficult for us to control the biological factors, as it is not easy to change the dynamics of how the virus acts within a body," Prof Cook added. "But we can change the social factors, such as the number of people a patient is exposed to, for example."

Prof Cook said the enhanced social distancing measures would be deemed successful if the number of daily cases falls to the single-digit zone by May 4, when the circuit-breaker phase ends.

"That would be a resounding success. If it were in the tens, I think we would be satisfied that we had brought it under control," he said. But if the number of new daily cases far exceeds this, stricter control measures may be required, he said.

"If the number of cases is much more than that, it would paint a rather pessimistic picture of our ability to control the pandemic here without much stricter policies."

But Prof Cook said that from now until then, there might be a delay before the enhanced social distancing measures take effect.

"This is because some people who are infected may not yet be symptomatic, and it can take a while before those who are symptomatic are diagnosed," he said.

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A version of this article appeared in the print edition of The Straits Times on April 09, 2020, with the headline How circuit breaker helps to prevent spread of coronavirus. Subscribe