Estimating SARS-CoV-2 transmission parameters between coinciding outbreaks in a university population and the surrounding community

Institutions of higher education faced a number of challenges during the COVID-19 pandemic. Chief among them was whether or not to re-open during the second wave of COVID-19 in the fall of 2020, which was controversial because incidence in young adults was on the rise. The migration of students back to campuses worried many that transmission within student populations would spread into surrounding communities. In light of this, many colleges and universities implemented mitigation strategies, with varied degrees of success. Washington State University (WSU), located in the city of Pullman in Whitman County, WA, is an example of this type of university-community co-location, where the role of students returning to the area for the fall 2020 semester was contentious. Using COVID-19 incidence reported to Whitman County, we retrospectively study the transmission dynamics that occurred between the student and community subpopulations in fall 2020. We develop a two-population ordinary differential equation mechanistic model to infer transmission rates within and across the university student and community subpopulations. We use results from Bayesian parameter estimation to determine if sustained transmission of COVID-19 occurred in Whitman County and the magnitude of cross-transmission from students to community members. We find these results are consistent with estimation of the time-varying reproductive number and conclude that the students returning to WSU-Pullman did not place the surrounding community at disproportionate risk of COVID-19 during fall 2020 when mitigation efforts were in place.