Changes in contact patterns shape the dynamics of the COVID-19 outbreak in China

TLDR

China imposed intense nonpharmaceutical interventions to curb COVID‑19 transmission, yet the interplay between age, contact patterns, social distancing, and susceptibility remains unclear as transmission rises elsewhere. The study analyzes contact survey data from Wuhan and Shanghai and contact‑tracing data from Hunan to investigate how contact patterns influence COVID‑19 dynamics. Using the collected contact data, the authors constructed a transmission model to evaluate the effects of social distancing and school closures on COVID‑19 spread. The model shows that daily contacts dropped seven‑to‑eightfold during social distancing, children 0‑14 were less susceptible (OR 0.34) while those over 65 were more susceptible (OR 1.47), and that social distancing alone sufficed to control the outbreak, with school closures further reducing peak incidence by 40‑60% and delaying the epidemic.

Abstract

Intense nonpharmaceutical interventions were put in place in China to stop transmission of the novel coronavirus disease 2019 (COVID-19). As transmission intensifies in other countries, the interplay between age, contact patterns, social distancing, susceptibility to infection, and COVID-19 dynamics remains unclear. To answer these questions, we analyze contact survey data for Wuhan and Shanghai before and during the outbreak and contact-tracing information from Hunan province. Daily contacts were reduced seven- to eightfold during the COVID-19 social distancing period, with most interactions restricted to the household. We find that children 0 to 14 years of age are less susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection than adults 15 to 64 years of age (odds ratio 0.34, 95% confidence interval 0.24 to 0.49), whereas individuals more than 65 years of age are more susceptible to infection (odds ratio 1.47, 95% confidence interval 1.12 to 1.92). Based on these data, we built a transmission model to study the impact of social distancing and school closure on transmission. We find that social distancing alone, as implemented in China during the outbreak, is sufficient to control COVID-19. Although proactive school closures cannot interrupt transmission on their own, they can reduce peak incidence by 40 to 60% and delay the epidemic.