Background:Live attenuated influenza vaccine (LAIV) is recommended for annual influenza vaccination in children from age 2 years. However, some guidelines recommend against its use in children with asthma or recurrent wheeze due to concerns over its potential to induce wheezing. Objective: To assess the safety of LAIV in children with moderate-severe asthma, and in preschool children with recurrent wheeze. Methods: Prospective, multi-center, open label, phase IV intervention studyin 14 specialist UK clinics.LAIV was administered under medical supervision, with follow-up of asthma symptoms 72 hours and 4 weeks late, using validated questionnaires.Clinical Trials.gov registration NCT02866942, EU Clinical Trials registration 2016-002352-24. Results: 478 young people (median 9.3, range 2–18 years) with physician-diagnosed asthma or recurrent wheeze were recruited, including 208 (44%) prescribed high-dose inhaled corticosteroids and 122 (31%) with severe asthma.There was no significant change in asthma symptoms in the 4 weeks following administration (median change 0, P=.26, McNemar’s test), with no impact of level of baseline asthma control/symptoms in predicting either a worsening of asthma or exacerbation following LAIV using a regression model. 47 subjects (14.7%, 95%CI 11% to 19.1%) reported a severe asthma exacerbation in the four weeks following immunization, requiring short course of systemic corticosteroids; in four cases, this occurred within 72 hours of vaccine. No association with asthma severity, baseline lung function or asthma control was identified.Conclusions: LAIV appears to be well-tolerated in the vast majority of children with asthma or recurrent wheeze, includingthosewhose asthma is categorized as severe or poorly controlled