Université de Paris, IAME, INSERM, Paris, France; Centre for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, France
Julie Bertrand
Université de Paris, IAME, INSERM, Paris, France
Oriol Mitjà
Fight AIDS and Infectious Diseases Foundation, Hospital Universitari Germans Trias i Pujol, Badalona, Spain; Lihir Medical Centre, International SOS, Londolovit, Papua New Guinea
Marc Corbacho-Monné
Fight AIDS and Infectious Diseases Foundation, Hospital Universitari Germans Trias i Pujol, Badalona, Spain; Hospital Universitari Parc Taulí, Sabadell, Spain; Facultat de Medicina–Universitat de Barcelona, Barcelona, Spain
Michael Marks
London School of Hygiene and Tropical Medicine, London, United Kingdom; Hospital for Tropical Diseases, London, United Kingdom; Division of infection and Immunity, University College London, London, United Kingdom
The relationship between SARS-CoV-2 viral load and infectiousness is poorly known. Using data from a cohort of cases and high-risk contacts, we reconstructed viral load at the time of contact and inferred the probability of infection. The effect of viral load was larger in household contacts than in non-household contacts, with a transmission probability as large as 48% when the viral load was greater than 1010 copies per mL. The transmission probability peaked at symptom onset, with a mean probability of transmission of 29%, with large individual variations. The model also projects the effects of variants on disease transmission. Based on the current knowledge that viral load is increased by two- to eightfold with variants of concern and assuming no changes in the pattern of contacts across variants, the model predicts that larger viral load levels could lead to a relative increase in the probability of transmission of 24% to 58% in household contacts, and of 15% to 39% in non-household contacts.
