Objectives: to determine factors associated with rates of SARS-CoV-2 infection and to determine whether anti-receptor-binding domain (RBD) IgG levels were associated with the rates of infectionDesign: prospective cohort of 34 months’ duration (February 2021 to December 2023)Setting: teachers and education workers working ≥8 hours per week in the Canadian province of OntarioParticipants: 3155 education workers were eligible for the risk factor analysis; 2977 for the serological analysisPrimary outcome measure: SARS-CoV-2 infection, symptomatic or asymptomaticResults: 1909 SARS-CoV-2 infections were reported (0.93 per 1000 participant-days); the highest incidence occurred during the period dominated by the Omicron BA.2 variant (2.01/1000 participant-days). After a median of 740 (interquartile range 361, 971) days of follow-up, participants who received three (adjusted hazard ratio (aHR) 0.24; 95% CI 0.11, 0.50; p<0.001), four (aHR 0.14; 95% CI 0.07, 0.30; p<0.001), or five or more (aHR 0.14; 95% CI 0.06, 0.30; p<0.001) doses of COVID-19 vaccines had lower rates of infection than participants who received <2 doses. Likewise, those who had immunity from a previous infection had lower rates of infection (aHR 0.05; 95% CI 0.04, 0.07) than those without. Participants 30 years of age or older had a lower rate of infection than participants 20-29 years old and those with Caucasian/European ancestry had a lower rate of infection (aHR 0.83; 95% CI 0.71, 0.96; p=0.01) than others. Also, compared to participants without known contact with an infected person, those in close contact with an infected household member (aHR 1.54; 95% CI 1.39, 1.71; p<0.001), coworker or student (aHR 1.22; 95% CI 1.04, 1.42, p=0.012), or individuals from more than one setting (aHR 1.45; 95% CI 1.29, 1.63; p<0.001) had higher rates of infection. Blood samples with anti-RBD antibody levels in the highest quintile (≥5850 BAU/mL) were associated with a lower rate of subsequent infection (aHR 0.40; 95% CI 0.23, 0.72) compared to samples with RBD levels below the threshold of detection. Conclusions: COVID-19 vaccines continued to provide protection against infection with SARS-CoV-2 through December 2023. Infection following exposure to people with SARS-CoV-2 occurred in a variety of venues indicating the need to practice intervention strategies when the potential for transmission is high.

The use of non-pharmaceutical interventions (NPIs) was imperative to avoid prolonged school closures during the COVID-19 pandemic. The purpose of this study was to understand the levels of adherence to and attitudes towards NPIs from February 2021 to December 2023 in schools in Ontario, Canada. Participants reported how frequently they, their coworkers, and their students used five NPIs: hand hygiene, covering coughs, staying home when ill, wearing a mask, and physically distancing. Open text comments provided participants with the option to provide additional details. A mixed methods approach incorporated a series of descriptive statistics calculated at consecutive time points and thematic analysis. Participants reported higher adherence to NPIs than their coworkers and students, with less than perfect adherence that declined over time. Six themes emerged from the analysis on NPI use in schools: 1) the influence of time; 2) managing competing priorities; 3) lack of enabling factors; 4) lack of reinforcing factors; 5) responsive use of NPIs; and 6) emotional toll. Poor use of hand hygiene, covering coughs, and staying home when ill indicate a need to improve these in schools as it would help reduce the transmission of communicable diseases and thereby reduce sick days for staff and students.