Predicting the impact of asymptomatic transmission, non-pharmaceutical intervention and testing on the spread of COVID19 COVID19

Ira B Schwartz; James H Kaufman; Kun Hu; Simone Bianco

The ongoing Coronavirus Disease-19 (COVID19) pandemic, caused by the novel RNA virus SARS-CoV-2 [1], has demonstrated the need for swift and effective non-pharmaceutical intervention (NPI) strategies [2, 3] . In the absence of a cure or a vaccine and given the nature of the virus transmission, drastic measures need to be implemented to reduce contacts and "flatten" the epidemic curve. As quarantine and social distancing are enforced, it is important to understand the impact of early release or relaxation of such interventions on the affected population. We use a mathematical model which explicitly considers a NPI such as sheltering in place or social distancing, similar to what has been widely implemented in several countries around the world. We calculate the effect on the epidemic of removing intervention as a function of time. The use of drastic NPI strategies in China reportedly reduced the basic reproductive number, R 0 , to a value smaller than 1, strongly curbing the epidemic within a short period of time [2] . In other countries, the implementation of such policies has not been as strict [3] , with an optimistic reduction in transmission by about half. To complicate the containment of the disease, early reports of pre-symptomatic and asymptomatic infections have emerged [4, 7] , with estimates of asymptomatic transmission of as much as 85% of all cases, and 55% per person. These predictions have been supported by recent studies [18] . The US CDC estimates the population of asymptomatic infections to 25% of all cases [5] .