Children’s respiratory symptoms and London’s Ultra Low Emission Zone: the CHILL cohort study

Abstract Background Traffic-related air pollution (TRAP) negatively affects children's respiratory health and development. Clean air zones such as London's Ultra Low Emission Zone (ULEZ) aim to reduce TRAP by discouraging high-polluting vehicles, but their health impacts remain unknown. Using the Children's Health in London and Luton (CHILL) cohort, we aim to evaluate the impact of the ULEZ on children's respiratory and allergy symptoms. Methods We recruited 3,414 children aged 6-9 years in London (intervention site) and Luton (comparator site) prior to the ULEZ. Parent-reported respiratory and allergy symptoms were collected annually (2018-2023) using the International Study of Asthma and Allergy in Childhood (ISAAC) questionnaire. Current symptoms were defined as having been experienced within the last 12 months and lifetime prevalence as having ever had (that condition). A generalised linear mixed effect model and logistic regression model with random effects were used to assess baseline prevalence of current and lifetime respiratory and allergy symptoms, respectively (adjusted for sex, ethnicity, socioeconomic deprivation and height). Results Across the study period, children in London had a 54% higher likelihood of current rhinitis (OR, 1.536; 95%CI, 1.200-1.969) compared to those in Luton. The prevalence of current wheeze, severe wheeze, and eczema symptoms did not differ between the two sites. The odds of a child ever having asthma were 58% lower in London than in Luton (OR, 0.584; 95%CI, 0.364-0.936), yet the odds of ever having eczema were 39% higher in London than in Luton (OR, 1.391; 95%CI, 1.009-1.919). Lifetime hayfever did not differ. Conclusions Preliminary analyses showed that current rhinitis and lifetime asthma differs between children in London and Luton. In further analyses, we will examine associations between air pollutants and these symptoms. Key messages • Air pollution has previously been shown to impact respiratory and allergy symptoms. • This study will allow us to assess the impact of air pollution and the ULEZ on these symptoms in children.