Different physical distance measures are effective in reducing the number of new cases of coronavirus, show the preliminary results of a modeling study carried out in a simulated framework of the city of Singapore.
Dr. Alex Cook and his colleagues at the National University of Singapore evaluated various scenarios of physical distance from three different contagion indices, also called basic reproduction rates (R0). This index shows the capacity of the virus to spread in the population.
If the R0 is less than 1, this means that one person infects on average less than another. The virus will therefore tend to disappear from the circulation by itself. Conversely, if the R0 is greater than 1, the virus tends to proliferate in the population.
In the three scenarios considered, the R0s were 1.5, 2, and 2.5, considered as low, medium, and high contagion indices.
hese simulations were carried out at the time when Singapore had 68 cases of coronavirus coming from outside, and 175 cases of transmissions inside this city-state of Asia. The researchers’ objective was to compare the different possible early interventions in Singapore.
The removal measures studied were:
- quarantine (infected people and their relatives);
- quarantine and school closings;
- quarantine and closure of workplaces.
The latter measure worked best, but it was the combination of the three that was most effective in reducing the number of new cases of SARS-CoV-2. And this is the path that Quebec has chosen to take.
All intervention scenarios were more effective in reducing the number of cases than those involving no intervention.
Not surprisingly, prevention and suppression become more difficult when the R0 values are high.
The authors note that the interpretation of their results remains limited since the exact index of contagion of the virus remains unknown.
The simulations show that the combined approach can prevent a national epidemic with relatively low contagion indices (R0 of 1.5). However, in higher contagion scenarios (Des R0 of 2.0 and 2.5) prevention becomes considerably more difficult. It reduces infections, but cases of transmission remain.
The researchers therefore believe that the implementation of a combined intervention of the three removal measures considerably reduces the number of SARS-CoV-2 infections.
They recommend the immediate deployment of this strategy if secondary transmission is confirmed in a region. However, according to them, quarantine and being away from the workplace should be given priority over closing schools at an early stage. The authors note that symptomatic children are usually taken out of school faster than symptomatic adults are from their workplace.
Studies also show that when the proportions of asymptomatic children are higher, the effectiveness of the intervention is considerably reduced.
Details of this work are published in The Lancet Infectious Diseases.