This study investigates the temporal dynamics of viral shedding and transmissibility of SARS-CoV-2 in 94 patients with laboratory-confirmed COVID-19 and models infectiousness profiles from 77 transmission pairs. Viral load was highest in throat swabs at symptom onset, suggesting infectiousness peaked on or before symptom onset. The study estimates that 44% of secondary cases were infected during the presymptomatic stage, particularly in settings with active case finding and quarantine. These findings indicate that control measures should account for presymptomatic transmission. SARS-CoV-2 has a basic reproductive number of 2.2-2.5, with transmission influenced by the serial interval and incubation period. The study found that infectiousness started 12.3 days before symptom onset and peaked at symptom onset. Presymptomatic transmission was estimated at 44%, with infectiousness declining quickly within 7 days. Sensitivity analyses showed that infectiousness peaked 2 days before to 1 day after symptom onset, with presymptomatic transmission ranging from 37% to 48%. The study also found that viral shedding decreased monotonically after symptom onset, consistent with previous studies. Transmission pairs showed a mean serial interval of 5.8 days, with 7.6% negative serial intervals. The estimated proportion of presymptomatic transmission was 44%, with infectiousness starting 2 days before symptom onset and peaking 2 days before to 1 day after symptom onset. The study highlights the importance of contact tracing and isolation in controlling outbreaks, especially in settings with active case finding. The findings suggest that enhanced personal hygiene and social distancing are key measures for community disease control. The study has limitations, including potential recall bias and the use of nationally promoted treatment protocols, which may have affected viral shedding patterns. In conclusion, the study estimates that viral shedding peaked on or before symptom onset, with a substantial proportion of transmission occurring before first symptoms. More inclusive contact tracing criteria are needed to capture potential transmission events 2-3 days before symptom onset for effective outbreak control.This study investigates the temporal dynamics of viral shedding and transmissibility of SARS-CoV-2 in 94 patients with laboratory-confirmed COVID-19 and models infectiousness profiles from 77 transmission pairs. Viral load was highest in throat swabs at symptom onset, suggesting infectiousness peaked on or before symptom onset. The study estimates that 44% of secondary cases were infected during the presymptomatic stage, particularly in settings with active case finding and quarantine. These findings indicate that control measures should account for presymptomatic transmission. SARS-CoV-2 has a basic reproductive number of 2.2-2.5, with transmission influenced by the serial interval and incubation period. The study found that infectiousness started 12.3 days before symptom onset and peaked at symptom onset. Presymptomatic transmission was estimated at 44%, with infectiousness declining quickly within 7 days. Sensitivity analyses showed that infectiousness peaked 2 days before to 1 day after symptom onset, with presymptomatic transmission ranging from 37% to 48%. The study also found that viral shedding decreased monotonically after symptom onset, consistent with previous studies. Transmission pairs showed a mean serial interval of 5.8 days, with 7.6% negative serial intervals. The estimated proportion of presymptomatic transmission was 44%, with infectiousness starting 2 days before symptom onset and peaking 2 days before to 1 day after symptom onset. The study highlights the importance of contact tracing and isolation in controlling outbreaks, especially in settings with active case finding. The findings suggest that enhanced personal hygiene and social distancing are key measures for community disease control. The study has limitations, including potential recall bias and the use of nationally promoted treatment protocols, which may have affected viral shedding patterns. In conclusion, the study estimates that viral shedding peaked on or before symptom onset, with a substantial proportion of transmission occurring before first symptoms. More inclusive contact tracing criteria are needed to capture potential transmission events 2-3 days before symptom onset for effective outbreak control.