High infectiousness immediately before COVID-19 symptom onset highlights the importance of continued contact tracing

Background Understanding changes in infectiousness during SARS-COV-2 infections is critical to assess the effectiveness of public health measures such as contact tracing. Methods Here, we develop a novel mechanistic approach to infer the infectiousness profile of SARS17 COV-2 infected individuals using data from known infector-infectee pairs. We compare estimates of key epidemiological quantities generated using our mechanistic method with analogous estimates generated using previous approaches. Results The mechanistic method provides an improved fit to data from SARS-CoV-2 infector infectee pairs compared to commonly used approaches. Our best-fitting model indicates a high proportion of presymptomatic transmissions, with many transmissions occurring shortly before the infector develops symptoms. Conclusions High infectiousness immediately prior to symptom onset highlights the importance of continued contact tracing until effective vaccines have been distributed widely, even if contacts from a short time window before symptom onset alone are traced. Funding Engineering and Physical Sciences Research Council (EPSRC)