1/3 New study shows that people with #COVID19 may be most infectious before their symptoms develop. The authors estimate that - on average - about 44% of secondary cases were infected from people who had not yet developed symptoms. https://www.nature.com/articles/s41591-020-0869-5

2/3 They report patterns of viral shedding in 94 patients with #COVID19 and model infectiousness from separate sample of transmission chains. They observed highest viral load in throat swabs at time of symptom onset; inferred that infectiousness peaked on or before symptom onset.

3/3 This has very important implications for case based interventions. These findings will make effective and aggressive contact tracing to test, trace new cases critical to controlling for outbreaks and future epidemic spread.