Assessment of Viral Shedding Week Following Administration of Live Attenuated Influenza Vaccine in Children

LAIV shedding studies in children could be an important way to confirm whether impediments to viral replication do indeed explain these observed reductions in vaccine effectiveness (VE), whether prior vaccination has any influence on replication and what future implications (if any) this might have for the UK paediatric LAIV programme. LAIV virus replication in children will be dependent on virological and host factors. The virus factors include replicative fitness of individual strains and the susceptibility to inhibition by other replicating strains (ability to compete). Host factors which may influence this include pre-existing specific immunity as a result of prior infection or previous vaccination (with either LAIV or IIV), and innate immune factors including mucosal immunity. There is significant variability in shedding across viral subtypes in studies done to date, so there is a need to obtain local data in a small pilot observational study which will look in detail at virus shedding by sequential daily virus samples, something not possible on a larger scale. The data generated will inform future LAIV studies in the UK in terms of optimum time of sample collection for viral shedding studies, which are likely to be required on a regular basis, to supplement field studies of vaccine effectiveness. This study will enrol up to 30 children that will allow these factors to be assessed. Both written informed consent from parent/ guardian and written assent from the child will be in place prior to any study procedure. All participants will have a baseline assessment of pre--existing influenza immunity (blood test, oral fluid collection and nasal swabs), followed by a single dose of LAIV. Parents will then be asked to take nasal swabs at home on days 1, 2, 3, 4, 5, 6, 7, 8, with further nasal swab, blood test and oral fluid collection in hospital 4 weeks later, in order to assess for immune responses to LAIV.