Symptom-Based Isolation Policies: Evidence from a Mathematical Model of Outbreaks of Influenza and COVID-19

Adam Burns; Alexander Gutfraind

Respiratory infections are the leading cause of death in low-or middle-income countries (LMICs) and account for an estimated four million deaths annually [1] . Before the recent emergence of SARS-CoV-2, much research focused on influenza, which causes worldwide annual epidemics of seasonal resulting in 3 to 5 million cases of severe illness, and approximately 250,000 to 500,000 deaths [2] . In the US, influenza causes on average of 226,000 hospitalizations and 3,000 to 49, 000 deaths each year [3, 4] . Control of influenza in children is an acute public health problem because attack rates (i.e., the proportion of the population infected) in unvaccinated children are estimated to average 12.7% [5] and exceed 30% during pandemic years [6] . Children also amplify the outbreak as they infect their peers and families, creating greater opportunities for further transmission in the community. [7, 8] For rapidly emerging outbreaks such as novel strains of influenza or SARS-CoV-2, pharmaceutical measures may be unavailable or less effective, and non-pharmaceutical intervention measures (NPIs) need to be used [9, 10] . NPIs are divided by the World Health Organization into categories of personal protection, social distancing, travel and environment measures [11] . However, when the WHO systematically reviewed all studies supporting each NPI for controlling pandemic influenza, it found gaps in the evidence base for many of the measures [11] . In this study, our goal is to use a computational model to examine the policy of symptom-based isolation -a form of social distancing. Under this NPI, individuals who are showing fever due to a respiratory infection are required to remain in isolation until their symptoms subside, normally followed by an additional period of one day free of fever (or antipyretic medications or steroids). The CDC currently recommends this NPI for controlling pandemic influenza and controlling influenza in schools [12, 13] . The buffer period of 1 day helps reduce transmission by keeping people in isolation when their fever symptoms temporarily subside. It also prevents transmission from viral shedding that often continues past the last episode of fever [14] . This NPI is often referred to as fever absenteeism or return-to-school policy in the context of schools.