Why estimating population-based case fatality rates during epidemics may be misleading

Lucas Böttcher; Mingtao Xia; Tom Chou

Besides under-reporting, the delay in transmission after becoming infected will also affect M 0 p (t). Although we have assumed that transmission occurs only after the incubation period when symptoms arise, there is evidence of asymptomatic transmission of coronavirus [26, 27] . Asymptomatic transmission can be modeled by setting β(τ ) > 0 even for τ < τ inc . An undelayed transmission in a nonquarantine scenario causes relatively more new infecteds who have not had the chance to die yet, leading to a smaller mortality ratio M 0 p (t). Within our SIR model, delaying transmission reduces the number of infected individuals and deaths at any given time but increases the measured mortality ratio M 0 p (t). Without quarantine, the asymptotic values M 0 p (∞) and CFR(∞) will also change as a result of changing the transmission latency period, as shown in the SI. With perfect quarantining, the asymptote M 0 p (∞) is eventually determined by a cohort that does not include new infections and is thus independent of the transmission delay.