Quarantining infected people, social distancing work to control spread of COVID-19

A new study conducted in a simulated Singapore setting reveals that efforts to contain the spread of the new coronavirus, COVID-19, can actually have a positive effect.

Specifically, quarantining infected people and their family members, closing schools plus quarantine and adopting workplace distancing plus quarantine, “in that order,” is an effective way to reduce cases of COVID-19.

The study was published in The Lancet Infectious Diseases by researchers from the National University of Singapore, who used an influenza epidemic simulation model to estimate the human-to-human spread of COVID-19 in a simulated Singaporean population. They investigated three infection reproduction values based on low, moderate or likely, and high infection transmissibility from Wuhan case data­­: RO=1.5, RO=2.0, and RO=2.5. They estimated infections at 80 days after 100 cases of community transmission were detected.

Researchers found prevention and suppression of the virus was more challenging with higher RO values. They did note limitations of the study, including dated census population data, impact of migrant movement, impact of transmission from outside of Singapore, contact patterns between individuals and other “unforeseen factors.”

The study found that the combined physical distancing method worked best at reducing the number of cases of COVID-19, though quarantine plus workplace measures was found to be the next best option. Quarantine plus school closure was the next best option, followed by quarantine only. Fortunately, all intervention scenarios were found to be better than no intervention at all.

In fact, the combined approach could prevent a national outbreak when transmission levels were relatively low (RO=1.5). At higher levels (RO=2.0 and RO=2.5), outbreaks were much harder to contain in the model.

“Should local containment measures, such as preventing disease spread through contact tracing efforts and, more recently, not permitting short-term visitors, be unsuccessful, the results of this study provide policy makers in Singapore and other countries with evidence to begin the implementation of enhanced outbreak control measures that could mitigate or reduce local transmission rates if deployed effectively and in a timely manner,” Alex R Cook, PhD, of the National University of Singapore, said in a statement.

For a baseline scenario, the lowest infection level of RO=1.5, the number of infections on day 80 was 279,000, or 7.4% of the population of Singapore. That’s compared to 727,000 cases under the value of RO=2.0, or 19% of the population, and 1,207,000 cases under the value of RO=2.5, or 32% of the population of Singapore.

With the combined intervention of quarantining infected people and their families, closing schools and having 50% of workers work from home, the number of infections dropped 99.3% to 1,800 cases with the value of RO=1.5. For RO=2.0, the numbers of cases dropped to 50,000, and for the value of RO=2.5, 258,000 cases were estimated.

“If the preventive effect of these interventions reduces considerably due to higher asymptomatic proportions, more pressure will be placed on the quarantining and treatment of infected individuals, which could become unfeasible when the number of infected individuals exceeds the capacity of health-care facilities,” Cooke said. “At higher asymptomatic rates, public education and case management become increasingly important, with a need to develop vaccines and existing drug therapies.”