Study population and setting
This study examined reported SARS-CoV-2 infections among parents, teachers, and teachers’ partners in Sweden from March 18 to June 15, 2020. During the study period, upper-secondary schools (school years 10-12, age 17-19 years) were engaged in online instruction, while lower-secondary schools (school years 7-9, age 14-16 years) continued to meet in person. The authors compared infections among parents/teachers/partners who were differentially exposed to in person school. The primary analysis included all parents in Sweden whose youngest child was in lower-secondary or upper-secondary school, excluding parents born outside the EU and Nordic countries (16% of all parents) out of a concern for selection bias (students with non-EU backgrounds are more likely to repeat upper-secondary years in preparatory programs). The analysis focused on the comparison between parents of the youngest children in the final year of lower-secondary or in the first year of upper-secondary school to minimize age-related confounding. Linear probability and logistic regression models were fit separately for the three populations under consideration (parents, teachers, and partners of teachers), with the outcome of interest being a positive SARS-CoV-2 test or a COVID-19 diagnosis. Models for parents were adjusted for age, sex, occupation, education, income, location of residence, and location of origin. Models for teachers and their partners were adjusted for the same covariates, and for partner and household characteristics.
Summary of Main Findings
Parents with a youngest child in the final year of lower-secondary school (in person) had an estimated 17% higher odds of SARS-CoV-2 infection (95% CI: 3% to 32%) relative to parents whose youngest child was in the first year of upper-secondary school (remote). No statistically significant association was seen in the odds of receiving a COVID-19 diagnosis after seeking healthcare. Lower-secondary school teachers had twice the odds (OR: 2.01, 95% CI: 1.52 to 2.67) of SARS-CoV-2 infection relative to upper-secondary school teachers. Partners of lower-secondary teachers also had higher odds of SARS-CoV-2 infection (OR: 1.29, 95% CI: 1.00 to 1.67). These estimates corresponded to an additional 1.05 infections per 1,000 parents, an additional 2.81 infections per 1,000 teachers, and an additional 1.47 infections per 1,000 partners of teachers. The results for parents, if assumed to be causal, imply that among the ~450,000 parents of lower-secondary students, closing schools would have decreased infections by 17% during the study period, excluding subsequent effects on transmission and epidemic growth. The authors conducted several robustness checks, and with some variations in magnitude of estimated effect, results were broadly similar.
Emphasizing the comparison between parents of children in adjacent school years reduced the possibility of age-related confounding. The availability of data from national registries meant that nearly all members of the target population were included in the analysis, though SARS-CoV-2 testing detected only a fraction of actual infections. The authors performed a broad array of tests to examine effect estimates under alternate assumptions, such as excluding health care workers who may have been occupationally exposed.
Because of limited testing capacity, estimates of additional reported infections may represent a small proportion of actual infections. Exclusion of parents from non-EU or Nordic countries resulted in better covariate balance between exposure groups, and the authors also fit models to the full parent population, but these families appear to have had higher infection risks overall, and in-person school may have had differential impacts in this group. The stated conclusion that overall impacts on transmission were minor and or/limited is not well substantiated in the absence of any estimation of subsequent extra-household transmission effects in the community.
By directly comparing parents and teachers of children differentially exposed to in-person school during the same time period, this study provides a reasonable estimate of increased reported SARS-CoV-2 infections associated with in-person secondary school.
This review was posted on: 19 March 2021