Recent reports have shown COVID-19 transmission prior to disease onset, raising concerns that people who appear healthy may
be major contributors to the COVID-19 pandemic. Few studies
have directly determined the proportion of transmission events
that occur before symptom onset, but a recent modeling study
by He et al. inferred that 44% of secondary cases were infected
during presymptomatic stages of disease. Here, we raise questions
regarding the approach and interpretation of the He et al. transmission model.
Although many factors are involved with transmission efficiency, it appears that asymptomatic/presymptomatic transmission measured by
direct contact tracing studies s lower than that predicted by
COVID-19 transmission models.