Age profile of susceptibility, mixing, and social distancing shape the dynamics of the novel coronavirus disease 2019 outbreak in China

Abstract

Strict interventions were successful to control the novel coronavirus (COVID-19) outbreak in China. As transmission intensifies in other countries, the interplay between age, contact patterns, social distancing, susceptibility to infection and disease, and COVID-19 dynamics remains unclear. To answer these questions, we analyze contact surveys data for Wuhan and Shanghai before and during the outbreak and contact tracing information from Hunan Province. Daily contacts were reduced 7-9 fold during the COVID-19 social distancing period, with most interactions restricted to the household. Children 0-14 years were 59% (95% CI 7-82%) less susceptible than individuals 65 years and over. A transmission model calibrated against these data indicates that social distancing alone, as implemented in China during the outbreak, is sufficient to control COVID-19. While proactive school closures cannot interrupt transmission on their own, they reduce peak incidence by half and delay the epidemic. These findings can help guide global intervention policies.

Figure 1.

A Regular weekday contact matrix for Wuhan. An alternative visualization of this contact matrix is shown in Appendix (Sec.11). B Outbreak contact matrix for Wuhan. C Difference between the regular weekday contact matrix and the outbreak contact matrix in Wuhan. D-F Same as A-C, but for Shanghai.

Figure 2.

A Estimated R₀ obtained with the outbreak contact matrix, as a function of baseline R₀ derived from the regular weekday contact matrix, where the transmission rate is held constant. The solid light grey rectangle represents the region where the R₀ in the outbreak situation is under the epidemic threshold. The shaded dashed black rectangle represents a plausible range of R₀ values in the early phase of the COVID-19 epidemic, as estimated in the literature. B Infection attack rate a year after the initial case of COVID-19 as a function of baseline R_0, derived from the regular weekday contact matrix. The corresponding value of R₀ for the outbreak situation can be seen in panel A. The shaded colored areas represent 95%CI. C As A, but for Shanghai only and including two scenarios of contact patterns reduction: (i) during vacations (Vacation) and (ii) during regular weekdays, after removing all contacts occurring in school setting (No schools). D Daily incidence of new infections for the four scenarios presented in panel C (median and 95%CI). The inset shows the mean infection attack rate after a year.