Evaluation of the safety of live attenuated influenza vaccine (LAIV) in children and adolescents with asthma and high-risk conditions: a population-based prospective cohort study conducted in England with the Clinical Practice Research Datalink

OBJECTIVES: To assess the safety of live attenuated influenza vaccine (LAIV) in children in high-risk groups. DESIGN: Non-interventional cohort study. SETTING: England during 2013–2014 and 2014–2015 influenza seasons. PARTICIPANTS: LAIV recipients identified from the Clinical Practice Research Datalink, aged 2–17 years, and with at least one underlying high-risk condition. LAIV recipients were matched with inactivated influenza vaccine (IIV) recipients and unvaccinated controls. PRIMARY OUTCOME MEASURES: Primary safety endpoints were any hospitalisation documented in the linked Hospital Episodes Statistics database within 42 days and up to 6 months after vaccination. RESULTS: 11 463 children and adolescents were included: 4718 received the trivalent LAIV formulation during the 2013–2014 influenza season and 6745 received the quadrivalent formulation during the 2014–2015 influenza season. The risks of hospitalisation within 42 days were 231 per 1000 person-years (95% CI 193 to 275) in season 2013–2014 and 231 (95% CI 198 to 267) in season 2014–2015. These risks were not significantly different when compared with matched unvaccinated children (relative risks (RR) 0.96 (95% CI 0.78 to 1.19) in season 2013–2014, 0.90 (95% CI 0.76 to 1.07) in season 2014–2015) and consistently lower than after IIV administration (RR 0.47 (95% CI: 0.37 to 0.59) in season 2013–2014, 0.42 (95% CI 0.35 to 0.51) in season 2014–2015). A similar pattern was observed up to 6 months postvaccination with a risk of hospitalisation after LAIV administration that did not differ from what was observed in unvaccinated controls and was lower than after IIV administration. CONCLUSIONS: This study did not identify new safety concerns associated with the administration of LAIV in children and adolescents with high-risk conditions. However, as with any other observational study, treatment administration was not randomly assigned and our findings may be confounded by differences between the groups at baseline. TRIAL REGISTRATION NUMBER: EUPAS18527.