Kristian Petrovic

Carrying out health research with schools can be both challenging and highly rewarding. Here we describe lessons learned from a research partnership lasting over 5 years, initially with 84 primary schools in London and Luton, and extended to 35 secondary schools, during our children health cohort study. This period included school closures and societal disruption during the COVID-19 pandemic, creating additional challenges to ongoing school participation. Our study involved annual health assessment visits to schools to test over 3000 participants and parental self-report questionnaires, to assess the potential benefits of air quality improvements arising from London Ultra Low Emission Zone (introduced in April 2019) on children’s lung development and health. Measures included height, weight, pre- and post- bronchodilator spirometry, physical activity monitoring, cognitive assessment, epigenetic markers of disease risk, SARS-CoV-2 IgE and IgM antibody testing, and heavy metals testing. The average annual participant attrition for our study was 11.6%. The acceptable threshold outlined in the initial protocol was 20%. All schools continued to participate in the study for 5 years. Central to the study success have been: shared agreement on the importance of the research topic; early preparatory work with stakeholders, a parallel engaging and innovative air pollution learning and outreach programme, incentivising school/teacher co-operation and parental questionnaire completion to boost response rates and mitigate non-response bias; and continuity of contact with the accessible and flexible research team. These successes form a template for other health research studies planning long-term engagement with schools.

The Ultra-Low Emission Zone (ULEZ), introduced in Central London in April 2019, aims to enhance air quality and improve public health. The Children's Health in London and Luton (CHILL) study evaluates the impact of the ULEZ on children's health. This analysis focuses on the one-year impacts on the shift towards active travel to school.
CHILL is a prospective parallel cohort study of ethnically diverse children, aged 6-9 years attending 84 primary schools within or with catchment areas encompassing London's ULEZ (intervention) and Luton (non-intervention area). Baseline (2018/19) and one-year follow-up (2019/20) data were collected at school visits from 1992 (58%) children who reported their mode of travel to school 'today' (day of assessment). Multilevel logistic regressions were performed to analyse associations between the introduction of the ULEZ and the likelihood of switching from inactive to active travel modes, and vice-versa. Interactions between intervention group status and pre-specified effect modifiers were also explored.
Among children who took inactive modes at baseline, 42% of children in London and 20% of children in Luton switched to active modes. For children taking active modes at baseline, 5% of children in London and 21% of children in Luton switched to inactive modes. Relative to the children in Luton, children in London were more likely to have switched from inactive to active modes (OR 3.64, 95% CI 1.21-10.92). Children in the intervention group were also less likely to switch from active to inactive modes (OR 0.11, 0.05-0.24). Moderator analyses showed that children living further from school were more likely to switch from inactive to active modes (OR 6.06,1.87-19.68) compared to those living closer (OR 1.43, 0.27-7.54).
Implementation of clean air zones can increase uptake of active travel to school and was particularly associated with more sustainable and active travel in children living further from school.