Modeling The Impact of Singapore’s ‘Circuit Breaker’

Interventions such as workplace distancing are crucial to controlling the virus’ spread when community transmission is observed, the study found.

AsianScientist (Apr. 16, 2020) – On January 20, a 66-year-old man carrying the SARS-CoV-2 virus—as it would later be known—arrived in Singapore on a flight from China’s Wuhan city, the epicenter of the coronavirus outbreak.

Two months since then, COVID-19 cases in Singapore have continued to rise, albeit slowly, and on April 3, Singapore Prime Minister Lee Hsien Loong implemented a ‘circuit-breaker’—a month-long closure of schools, workplaces and non-essential services.

These measures may have a serious impact on Singapore’s economy, but a recent study led by researchers from the National University of Singapore (NUS) Saw Swee Hock School of Public Health suggests why the Singapore government might be on the right track.

The study, published in the journal The Lancet, found that early interventions such as quarantine and workplace distancing are crucial to controlling the virus’ spread should community transmission is observed—that is, if transmissions can no longer be traced to a single individual.

When COVID-19 began to spread rapidly out of Wuhan, China’s authorities implemented social distancing measures and a travel ban. A study published in Science concluded that the measures China took may have helped to prevent more than 700,000 infections across the country.

Hence, to help policymakers plan ahead, the NUS team sought to investigate the effectiveness of a nationwide intervention in Singapore. To begin, the team simulated a Singaporean population using national 2010 census data, and adapted an influenza epidemic simulation model to estimate the likelihood of human-to-human transmission of SARS-CoV-2.

Using this model, they ran multiple simulations and adjusted different parameters in each run, such as how infectious the virus was, or which interventions were in place. In some cases, the data was far from hopeful.

Taking a range of basic reproduction number (R0) of the virus, which is a measure of the virus’s potential to spread, and assuming 7.5 percent of infections are asymptomatic, the cumulative median number of cases at day 80 ranged between 279,000 to 1,207,000—up to 32 percent of Singapore’s total population—when R0 ranged from 1.5 to 2.5.

But when nationwide interventions, which include home quarantine, workplace distancing and school closures, were implemented, infection numbers dropped by as much as 99.3 percent.

Importantly, even when infectivity was dialed to the highest (R0 of 2.5), substantial reductions of up to 78.2 percent may be observed when those interventions were in place, especially when the three measures were collectively implemented. Nevertheless, the researchers recommend that home quarantines and workplace distancing should be prioritized over school closures as workplace infections are key to disease transmission.

These findings, however, come with a caveat—asymptomatic individuals who unknowingly spread the disease. Acknowledging this, the researchers performed the simulations with different proportions of asymptomatic cases, from 22.7 percent to 50 percent of cases. They found that, as asymptomatic patients increase, the preventive effect of early interventions would be significantly reduced. In such cases, the team recommended diverting the focus towards public education and case management, as well as on vaccine and drug development.

In conclusion, the authors stressed that public cooperation was particularly crucial for three groups: older individuals, immunocompromised individuals and those with pre-existing conditions.

“Current government-led outbreak control measures will only be successful with public cooperation through exercising good hygiene, infection prevention in shared spaces, and adequate education to understand when symptoms might be indicative of a potential SARS-CoV-2 infection,” they wrote.

The article can be found at: Khoo et al. (2020) Interventions to mitigate early spread of SARS-CoV-2 in Singapore: a modelling study.


Copyright: Asian Scientist Magazine; Illustration: Shelly Liew/Asian Scientist Magazine.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Lim Zeng Hao completed a degree in biological sciences at Nanyang Technological University, Singapore. In his spare time, he dabbles in new languages and daydreams about the eventual publication of his epic fantasy book series. Zeng Hao is a science writer with Asian Scientist Magazine.

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