Incidence of live-attenuated influenza vaccine administration beyond expiry date in children and adolescents aged 2–17 years in the UK: a population-based cohort study

OBJECTIVES To estimate the proportion of live-attenuated influenza vaccine (LAIV) doses administered beyond expiry date in children and adolescents during influenza seasons 2013-2014 and 2014-2015 in the UK. DESIGN This was a retrospective cohort study. Two cohorts of children and adolescents who received LAIV from 1 September 2013 to 31 March 2014 and from 1 September 2014 to 31 March 2015 and aged 2-17 years at time of LAIV administration were identified from the Clinical Practice Research Datalink (CPRD). SETTING More than 500 primary care practices in the UK. POPULATION Proportions of vaccine doses administered beyond expiry date were assessed among 47 396 and 67 099 LAIV recipients with a documented vaccine lot identifier in influenza seasons 2013-2014 and 2014-2015, respectively. INTERVENTION None. MAIN OUTCOME MEASURE Administrations of expired LAIV were ascertained by comparison of vaccination dates in CPRD records with expiration dates in AstraZeneca/MedImmune lot distribution data. RESULTS Overall, 245 LAIV recipients, 80 in 2013-2014 and 165 in 2014-2015, received a dose after its expiration date, yielding proportion estimates of 1.7 per 1000 doses (95% CI 1.3 to 2.1) in season 2013-2014 and 2.5 per 1000 (95% CI 2.1 to 2.8) in season 2014-2015. This proportion increased above 1.0% after December during each season. Most (84% in influenza season 2013-2014 and 59% in influenza season 2014-2015) received an expired dose <30 days after its expiration date. The proportion was higher in London (relative risk 1.93 (95% CI 1.25 to 2.99)) and when the number of LAIV recipients registered in the practice was lower than the median number per practice (relative risk 2.69 (95% CI 1.99 to 3.62)). CONCLUSIONS Administration of expired LAIV doses occurs infrequently.