BACKGROUND: Understanding differences in the seasonality of bronchiolitis can help to plan the timing of interventions. We quantified the extent to which seasonality in hospital admissions for bronchiolitis is modified by socioeconomic position. METHODS: Using Hospital Episode Statistics, we followed 3Β 717Β 329 infants born in English National Health Service hospitals between 2011 and 2016 for 1 year. We calculated the proportion of all infant admissions due to bronchiolitis and the incidence rate of bronchiolitis admissions per 1000 infant-years, according to year, month, age, socioeconomic position and region. We used harmonic Poisson regression analysis to assess whether socioeconomic position modified bronchiolitis seasonality. RESULTS: The admission rate for bronchiolitis in England increased from 47.4 (95% CI 46.8 to 47.9) to 58.9 per 1000 infant-years (95% CI 58.3 to 59.5) between 2012 and 2016. We identified some variation in the seasonality of admissions by socioeconomic position: increased deprivation was associated with less seasonal variation and a slightly delayed epidemic peak. At week 50, the risk of admission was 38% greater (incidence rate ratios 1.38; 95% CI 1.35 to 1.41) for infants in the most deprived socioeconomic group compared with the least deprived group. CONCLUSION: These results do not support the need for differential timing of prophylaxis or vaccination by socioeconomic group but suggest that infants born into socioeconomic deprivation should be considered a priority group for future interventions. Further research is needed to establish if the viral aetiology of bronchiolitis varies by season and socioeconomic group, and to quantify risk factors mediating socioeconomic deprivation and bronchiolitis rates
