SARS-CoV-2 seroprevalence among Vancouver public school staff in British Columbia, Canada

Abstract

Importance: Contact-tracing studies suggest minimal secondary transmission in schools. However, there are limited school data accounting for asymptomatic cases, particularly late in the 2020/21 school year, and in the context of uninterrupted in-person schooling and widespread community transmission. Objectives: To determine the SARS-CoV-2 seroprevalence in a sample of school staff, compared to the community, and to COVID-19 rates among all students and staff within the same school population. Design: Incident COVID-19 cases among students and school staff using public health data, with an embedded cross-sectional serosurvey among school staff sampled from February 10 to May 15, 2021, comparing to age, sex and geographic location-matched blood donors sampled in January 2021. Setting: Vancouver School District (British Columbia, Canada) from kindergarten to grade 12. Participants: Active school staff enrolled from February 3 to April 23, 2021. Main outcome measures: SARS-CoV-2 antibodies in a sample of school staff using spike (S)-based testing (unvaccinated staff) or N-based serology testing (vaccinated staff). Results: The incidence of COVID-19 cases among students attending in-person was 9.8 per 1,000 students during the 2020/21 school year (N = 47,280 students), and among staff was 13 per 1,000 since the beginning of the pandemic (N = 7,071 active school staff). In total, 1,689 school staff (64% elementary, 28% secondary, 8.3% school board staff or multiple grades) completed the questionnaire, 78.2% had classroom responsibilities, and spent a median of 17.6 hours in class per week [IQR: 5.0 - 25 hours]. Although 21.5% (363/1,686) reported close contact with a COVID-19 case, only 1.4% (24/1688) of the school staff reported having had a positive viral nucleic acid test. Of this group, five believed they acquired the infection at school. The adjusted seroprevalence in staff who gave blood (1,556/1,689, 92.1%) was 2.3% [95%CI: 1.6 - 3.2%] compared to 2.3% [95%CI: 1.7 - 3.0%] in blood donors. Conclusion and relevance: Despite high reported COVID-19 cases among students and staff, and frequent within-school exposures, we found no detectable increase in seroprevalence among school staff above the community seroprevalence. These findings corroborate claims that, with appropriate mitigation strategies, in-person schooling is not associated with significantly increased risk for school staff.

Seroprevalence of SARS-CoV-2 in German secondary schools from October 2020 to July 2021: a longitudinal study

“…While our study is one of the largest studies to report seroprevalence estimates in the student population in the later phase of the pandemic, the results are in line with a seroprevalence study in teachers showing no differences compared to a matched sample of blood donors [ 23 ] or to register data showing only minimal consequences for overall transmission if schools are kept open [ 12 ]. The regional differences in seroprevalence also support this finding.…”

Changing Patterns of SARS-CoV-2 Seroprevalence among Canadian Blood Donors during the Vaccine Era

“…To date we have published one report from our study that described seroprevalence in the first wave of the pandemic ( 7 ). Other Canadian serosurveys have been carried out over limited time periods and relied on blood spots for serology ( 11 , 12 ) or have been limited to specific regions ( 13 , 14 ) and/or populations ( 15 – 17 ). In other countries, such as the United States, blood donors are central to national monitoring of infections and vaccine seroprevalence ( 5 , 18 ) but have not published data on vaccine-related antibody concentrations.…”

COVID-19 Vaccine Intentions and Perceptions Among Public School Staff of the Greater Vancouver Metropolitan Area, British Columbia, Canada

“…Human resources data obtained from the 2 out of the 3 participating school districts show that the age and sex of respondents to the current vaccine survey were representative of the target population (target population had a mean age of 46.4 yrs and 73.6% were female). The sample was also previously reported to be representative of the target population based on geographical residence and COVID-19 positivity ( 12 ).…”

“…First, approximately 17% of eligible school district staff participated in the present study; however, the study was designed to capture a representative sample of district staff within a short and defined time period and had a high response rate (95.4%) among participants of the parent seroprevalence study. In addition, we found that the study sample was representative of the target population on age, sex, geographical residence and COVID-19 infection rates ( 12 ), although selection bias related to other criteria may influence vaccine intentions. Second, the current study focused on intentions to receive the first dose of the COVID-19 vaccines and it is not known how intentions may differ toward the second or subsequent doses or how emerging news of side effects (e.g., risk of blood clots) may impact hesitancy.…”

“…Current, active staff members of three school districts in the Greater Vancouver Metropolitan Area were surveyed about vaccine intention as part of a seroprevalence study ( 12 ). District staff were recruited in the main seroprevalence study through an advertisement posted to the district websites and emailed directly to staff by school principals, inviting them to self-register online via the study website.…”