Strongly heterogeneous transmission of COVID-19 in mainland China: local and regional variation

Yuke Wang; Peter F.M. Teunis

The copyright holder for this preprint . number estimates were grouped by gender, no differences were found. Similarly, estimates of transmission from different age groups showed that small children and elderly people were equally likely to transmit infection as any other age group ( Figure A3 ). We also examined the effect of the size of clusters imputed on the results and the difference was trivial between average cluster size three and five. An important issue in analyzing transmission of COVID-19 is the amount of silent transmission. As mentioned earlier, some infectious subjects may transmit their infection before they become symptomatic. As long as their descendant cases also go on to develop symptoms their transmission link may still be established. However, when infected subjects who remain completely asymptomatic could be infectious to susceptible contacts, the appearance of such contacts, when symptomatic, could not be linked to their immediate ancestors. Given the fact that symptoms seem to be milder in those who are young, such unobservable transmission cannot be excluded [26] . Silent transmission has been seen in other infectious diseases [27] where, notably, asymptomatically infected subjects appeared to cause fewer transmission. As asymptomatic infections would lead to an antibody response, serology could be a valuable tool to assess the importance of asymptomatic transmission.