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.