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Additional file 1: Fig. S1. Time series and predicting epidemic magnitude of CVA16 activity in Anhua county during 2013-2016 (A) and that in Hunan province during 2009-2018 (B). Fig. S2. Participants’ included time in baseline and follow-up times (A) and the epidemic seasons of CVA16 activity during 2009-2018 in Anhua, Hunan province (B). Fig. S3. Distribution of maternal antibody titre transfer ratio against CVA16 for all pairs of neonate-mother (A) and positive mothers with antibody titre ≥8 (B). Fig. S4. The aggregated maternal titre specified transfer ratio. Fig. S5. Maternal antibody titre transfers efficacy against CVA16. Fig. S6. Transfer ratio trend with all pairs of mother-neonate. Fig. S7. Dynamic of seroprevalence, neutralization antibody titre by age for neonates using 16 as positive threshold. Fig. S8. Dynamic of neutralization antibody titre by age for neonates using full follow-up subset. Fig. S9. Dynamics of neutralization antibody titer by age for neonates stratified by maternal antibody levels. Fig. S10. Waning rate of maternal transmitted CVA16 antibody and natural infection induced antibody. Fig. S11. Age distribution and cumulative distribution of HFMD associated to CVA16 by clinical severity in Hunan province during 2009-2018 and Anhua county during 2013-2016. Table S1. Distribution of participants aged 1-9 years and sampling ratio. Table S2. Seasonality comparison between Anhua county and Hunan province. Table S3. Epidemic duration for CVA16 circulation in Anhua. Table S4. (a) Baseline characteristics of mothers and neonates in neonate cohort between participants and non-participants, selected participants and non-selected participants for CVA16 assay. (b) Baseline characteristics of neonates in neonate cohort between full follow-up participants and incomplete follow-up participants. Table S5. Comparison of baseline characteristics of 1-9 years old children between participants and non-selected objects through sampling, full follow-up and incomplete follow-up. Table S6. Seroprevalence and GMT of mothers and neonates at birth. Table S7. Sample size (n, %) for CVA16 antibody transfer ratio analysis. Table S8. Multivariate analysis with factors associated with neonates’ seropositivity, antibody titre at birth and transfer ratio. Table S9. Univariate analysis with factors associated with neonates’ seropositivity at birth. Table S10. Univariate analysis with factors associated with the transfer ratio of maternal antibody. Table S11. Univariate analysis with factors associated with neonates’ antibody titre at birth. Table S12. Sensitive analysis for multivariate analysis with factors associated with maternal antibody transfer ratio. Table S13. Sensitive analysis of median age of neonate with positive antibody. Appendix.

A long-standing question in infectious disease dynamics concerns the role of transmission heterogeneities, driven by demography, behavior and interventions. Based on detailed patient and contact tracing data in Hunan, China we find 80% of secondary infections traced back to 15% of SARS-CoV-2 primary infections, indicating substantial transmission heterogeneities. Transmission risk scales positively with the duration of exposure and the closeness of social interactions and is modulated by demographic and clinical factors. The lockdown period increases transmission risk in the family and households, while isolation and quarantine reduce risks across all types of contacts. The reconstructed infectiousness profile of a typical SARS-CoV-2 patient peaks just before symptom presentation. Modeling indicates SARS-CoV-2 control requires the synergistic efforts of case isolation, contact quarantine, and population-level interventions, owing to the specific transmission kinetics of this virus., One Sentence Summary: Public health measures to control SARS-CoV-2 could be designed to block the specific transmission characteristics of the virus.

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.