INTRODUCTION: Influenza vaccination through primary care has been recommended for all preschool children in the UK since 2013 as part of a universal immunisation programme. Vaccination is required annually and effectiveness varies by season. Factors associated with influenza vaccine receipt and those for other childhood vaccines may therefore differ. METHODS: We used The Health Improvement Network, a large primary care database, to create a cohort of children in England and Wales aged 2-4 years eligible for vaccination in the 2014/2015 season. Mixed-effects Poisson regression models were used to determine sociodemographic and clinical factors associated with influenza vaccine receipt, allowing for practice-level variation. RESULTS: Overall, 38.7% (95% CI 38.3% to 39.1%) of 57 545 children were vaccinated against influenza. Children in the poorest deprivation quintile were 19% less likely to receive influenza vaccine than those in the wealthiest quintile (adjusted risk ratio (ARR) 0.81, 95% CI 0.77 to 0.86). Children who received a timely first dose of measles-mumps-rubella vaccine were twice as likely to receive influenza vaccine (ARR 2.00 95% CI 1.87 to 2.13). Being 4 years old, not in a clinical risk group, or living with 2 or more other children were also significantly associated with a lower probability of vaccination. DISCUSSION: Children living in areas of higher deprivation and in larger families are less likely to receive influenza vaccine. Further research is required into whether interventions, such as offering vaccinations in other settings, could increase uptake in children, particularly in deprived areas
