Table 1. Key parameters and definitions for modeling of coronavirus disease.

Parameter	Definition
Basic reproduction number (R0)	Average number of persons infected by a single infected individual in a fully susceptible population
Time-varying or effective reproduction number (R, Rt, RE)	Average number of persons infected by an infected individual in a population in the context of changing transmission patterns, such as those resulting from interventions and acquired immunity
Incubation period	Time between infection and symptom onset
Serial interval	Average time between symptom onset in a primary case and symptom onset in linked secondary cases
Generation interval	Average time between infection of a primary case and infection of linked secondary cases
Doubling time	Average time for the daily case count to double
Infectious period	Period during which an infected host, with or without symptoms, can transmit an infectious agent to susceptible persons, directly or indirectly
Case-fatality ratio	Proportion of cases that result in death (with case defined in numerous ways)
Infection-fatality ratio	Proportion of all infections (confirmed, symptomatic, asymptomatic) that result in death
Mean evolutionary rate	Average rate at which mutations accumulate per base pair in the genome over the course of a year