The time scale of asymptomatic transmission affects estimates of epidemic potential in the COVID-19 outbreak

Sang Woo Park; Daniel M Cornforth; Jonathan Dushoff; Joshua S Weitz

We explore the effects of different assumptions about speed and effectiveness of asymptomatic transmission on the importance of asymptomatic transmission and estimates of the basic reproduction number R 0 , using a gamma assumption (see Methods). Across the range of parameters we explore, the intrinsic proportion of asymptomatic transmission z is similar to the realized proportion q ( Figure 1A ). As the relative mean generation interval of asymptomatic transmission,Ḡa /Ḡs , increases, q decreases because symptomatic cases are more likely to have short generation intervals, which drive the spread during the growth phase ( Figure 1A ). In Figure S1 , we present the same figure but showing differences between the realized and the intrinsic proportion of asymptomatic transmission, q − z. Figure 1B shows the effect of different assumptions about the generation interval of asymptomatic cases,Ḡa , on the estimated basic reproduction number R 0 . WhenḠa is long compared toḠs , then we are effectively assuming a longer mean for the overall generation interval. This assumption leads to a larger estimate of R 0 for a fixed value of r (see [18] ).