Several mechanisms driving SARS-CoV-2 transmission remain unclear . Based on individual records of 1178 potential SARS-CoV-2 infectors and their 15,648 contacts in Hunan, China, we estimated key transmission parameters . The mean generation time was estimated to be 5.7 (median : 5.5, IQR : 4.5 , 6.8) days, with infectiousness peaking 1.8 days before symptom onset, with 95% of transmission events occurring between 8.8 days before and 9.5 days after symptom onset . Most transmission events occurred during the pre-symptomatic phase (59.2 %). SARS-CoV-2 susceptibility to infection increases with age, while transmissibility is not significantly different between age groups and between symptomatic and asymptomatic individuals . Contacts in households and exposure to first-generation cases are associated with higher odds of transmission . Our findings support the hypothesis that children can effectively transmit SARS-CoV-2 and highlight how pre-symptomatic and asymptomatic transmission can hinder control efforts.