No abstract

We report temporal patterns of viral shedding in 94 laboratory-confirmed COVID-19 patients and modelled COVID-19 infectiousness profile from a separate sample of 77 infector-infectee transmission pairs. We observed the highest viral load in throat swabs at the time of symptom onset, and inferred that infectiousness peaked on or before symptom onset. We estimated that 44% of transmission could occur before first symptoms of the index. Disease control measures should be adjusted to account for probable substantial pre-symptomatic transmission.

and colleagues at ETH Zurich very helpfully alerted us to a syntactical error in our original code, specifically that the likelihood as we had originally specified gave rise to zero probability for two transmission pairs with the most negative serial intervals. Following their lead, we also applied a normalization factor in the likelihood to account for the uncertainty in the symptom-onset dates of the index cases. However, assuming a uniform distribution, the likelihood would differ only by a multiplicative constant and would give the same estimates. We used the bootstrap method to estimate the 95% confidence intervals (CIs).