SEMIPARAMETRIC MODELING OF SARS-COV-2 TRANSMISSION USING TESTS, CASES, DEATHS, AND SEROPREVALENCE DATA

Mechanistic models fit to streaming surveillance data are critical for understanding the transmission dynamics of an outbreak as it unfolds in realtime. However, transmission model parameter estimation can be imprecise, sometimes even impossible, because surveillance data are noisy and not informative about all aspects of the mechanistic model. To partially overcome this obstacle, Bayesian models have been proposed to integrate multiple surveillance data streams. We devised a modeling framework for integrating SARS-CoV-2 diagnostics test and mortality time series data as well as seroprevalence data from cross-sectional studies and tested the importance of individual data streams for both inference and forecasting. Importantly, our model for incidence data accounts for changes in the total number of tests performed. We apply our Bayesian data integration method to COVID19 surveillance data collected in Orange County, California, between March 2020 and February 2021 and find that 32–72% of the Orange County residents experienced SARS-CoV-2 infection by mid-January, 2021. Despite this high number of infections, our results suggest that the abrupt end of the winter surge in January 2021 was due to both behavioral changes and a high level of accumulated natural immunity.