QUANTIFYING SARS-CoV-2 INFECTION KINETICS from UNVACCINATED and VACCINATED PERSONS

ABSTRACT

Background: Transmission of SARS-CoV-2 is highly heterogeneous, with a small fraction of infected individuals (often referred to as "superspreaders") contributing a disproportionate share of forward transmission. Numerous behavioral and environmental explanations have been offered to explain transmission heterogeneity, but the extent to which the underlying features of the infection process within individual hosts contribute towards the superspreading phenomenon remains unclear. In addition, it is not clear how vaccination would impact on the viral infection dynamics and thus the infectiousness of individuals. Addressing these gaps in knowledge will inform the design of more targeted and effective strategies for controlling community spread. Methods: In a study on UIUC campus (UIUC SHIELD), the dynamics of infectious virus and viral RNA shedding were captured through daily longitudinal sampling of 72 individuals for up to 14 days (60 unvaccinated and 12 vaccinated). We fitted mechanistic models to both viral loads and cell culture positivity data, and directly estimated viral reproduction and clearance rates, and overall infectiousness for each individual. Results: Integrating mathematical models with viral load and cell culture positivity data, we show a substantial level of heterogeneity in infectiousness of individual. In unvaccinated individuals, peak viral loads and clearance kinetics of B.1.1.7 and non-variant of concern viruses were indistinguishable. In vaccinated individuals, the viral dynamics do not follow typical patterns of acute infection dynamics and we estimate that these individuals are much less infectious than unvaccinated individuals. Conclusion: Our work provides a high-resolution portrait of SARS-CoV-2 infection dynamics. Significant person-to-person variation in infectious virus shedding suggests that individual-level heterogeneity in viral dynamics contributes to superspreading. Vaccinated individuals are less infectious than unvaccinated individuals overall.