Investigation of the Efficiency of Mask Wearing, Contact Tracing, and Case Isolation During the COVID-19 Outbreak

Abstract

Background: Case isolation and contact tracing are two essential parts of control measures to prevent the spread of COVID-19. Recent studies have shown that asymptomatic and pre-symptomatic transmissions play an important role in the ongoing SARS-CoV-2 pandemic, which makes outbreak control only through contact tracing and case isolation very difficult. Additional interventions, such as mask wearing, are required. There are various approaches to mask usage during the epidemic and, correspondingly, their effects on disease transmission may differ. We modelled the effects of different interventions on the disease spread and showed that high mask wearing coverage can lead to a better control of the outbreak, even in the absence of a lockdown. Methods: A stochastic model of COVID-19 propagation was implemented in order to estimate the effectiveness of mask wearing in addition to case isolation and contact tracing. It is assumed that after isolation, an infected person cannot transmit the virus anymore. We varied the percentage of mask efficiency and the percentage of people wearing masks and investigated three different approaches towards mask usage: the mask prevents spreading of the infection, and an infected person only starts wearing it after the onset of symptoms; the mask prevents spreading and all people wear masks; all people wear masks, and the mask prevents spreading and protects healthy persons from getting infection. We estimated the effect of mask wearing together with other interventions on the basic reproduction number (R0) and calculated the effective reproduction number after implementation of interventions. We also simulated the possibility of controlling the outbreak. An outbreak was defined as being controlled if it did not exceed a total of 5000 cases over three months and no new cases were found in the following fourth month. Findings: For the 20 initial symptomatic cases, with 40% pre-symptomatic transmission and a R0 = 2·5 , the outbreak could not be controlled even with 100% contact tracing. Wearing of masks only after symptom onset added only a very small improvement on the pandemic situation and cannot be used to control the outbreak. When all people wear masks and it is assumed that a mask prevents spreading and protects healthy individuals, then there is almost 70% probability of outbreak control even without contact tracing. The probability of control increases with an increase in the number of traced contacts. As a result, with 60% efficiency of contact tracing, the outbreak can be controlled with almost 100% probability. When initial number of asymptomatic cases is equal to the number of symptomatic cases, then an almost completely controlled outbreak is achieved when 70% of all people wear masks and 60% of infected individuals (with symptoms) are traced. Similar results can be achieved for larger number of total initial cases. Interpretation: With a large proportion of infectiousness before the onset of symptoms (40%) and the presence of asymptomatic cases, three investigated interventions (isolation of cases, contact tracing, and mask wearing by all people) are sufficient to control the disease spread within three months. A high probability of mask wearing by both infected and healthy people, even in presence of asymptomatic individuals, significantly increased the probability of controlling the outbreak even with only modest effectiveness of contact tracing. This shows that a second wave of COVID-19 could be avoided by tracing contacts and through the use of masks. Funding Statement: This work was supported in part by NHRI (National Health Research Institutes, Taiwan, project number BN-106-PP-08) and MOST (Ministry of Science and Technology, Taiwan, project number MOST 106 2115 M 400 001). Declaration of Interests: The authors declare no comparing interests.