Impact of routine asymptomatic screening on COVID-19 incidence in a highly vaccinated university population

BackgroundWith the return of in-person classes, an understanding of COVID-19 transmission in vaccinated university campuses is essential. Given the context of high anticipated vaccination rates and other measures, there are outstanding questions of the potential impact of campus-based asymptomatic screening. MethodsWe estimated the expected number of cases and hospitalizations in one semester using rates derived for British Columbia (BC), Canada up to September 15th, 2021 and age-standardizing to a University population. To estimate the expected number of secondary cases averted due to routine tests of unvaccinated individuals in a BC post-secondary institution, we used a probabilistic model based on the incidence, vaccination effectiveness, vaccination coverage and R0. We examined multiple scenarios of vaccine coverage, screening frequency, and pre-vaccination R0. ResultsFor one 12 week semester, the expected number of cases is 67 per 50,000 for 80% vaccination coverage and 37 per 50,000 for 95% vaccination coverage. Screening of the unvaccinated population averts an expected 6-16 cases per 50,000 at 80% decreasing to 1-2 averted cases per 50,000 at 95% vaccination coverage for weekly to daily screening. Further scenarios can be explored using a web-based application. InterpretationRoutine screening of unvaccinated individuals may be of limited benefit if vaccination coverage is 80% or greater within a university setting.

SARS-CoV-2 transmission in K-12 schools in the Vancouver Coastal Health Region: a descriptive epidemiologic study

BackgroundThere is an urgent need to assess the role of schools in the spread of SARS-CoV-2 in Canada to inform public health measures. We describe the epidemiology of SARS-CoV-2 infection in students and staff in the Vancouver Coastal Health (VCH) region in the first three months of the 2020/2021 academic year, and examine the extent of transmission in schools. MethodsThis descriptive epidemiologic study using contact tracing data included all SARS-CoV-2 cases reported to VCH between September 10 and December 18, 2020 who worked in or attended K-12 schools in-person. Case and cluster characteristics were described. ResultsThere were 699 school staff and student cases during the study period, for an incidence of 55 cases per 10,000 population, compared to 73 per 10,000 population in all VCH residents. Among VCH resident staff and student cases, 53% were linked to a household case/cluster, <1.5% were hospitalized and there were no deaths. Out of 699 cases present at school, 26 clusters with school-based transmission resulted in 55 secondary cases. Staff members accounted for 54% of index cases (14/26) while comprising 14% of the school population. Among clusters, 88% had fewer than 4 secondary cases. InterpretationCOVID-19 incidence in the school population was lower than that of the general population. There were no deaths and severe disease was rare. School-based transmissions of SARS-CoV-2 were uncommon and clusters were small. Our results support the growing body of evidence that schools do not play a major role in the spread of SARS-CoV-2.