Efficacy and effectiveness of live attenuated influenza vaccine in school-age children

Abstract

Evidence of high efficacy of live attenuated influenza vaccine (LAIV) from randomized controlled trials is strong for children 2–6 years of age, but fewer data exist for older school-age children. We reviewed the published data on efficacy and effectiveness of LAIV in children ≥5 years. QUOSA (Elsevier database) was searched for articles published from January 1990 to June 2014 that included ‘FluMist’, ‘LAIV’, ‘CAIV’, ‘cold adapted influenza vaccine’, ‘live attenuated influenza vaccine’, ‘live attenuated cold adapted’ or ‘flu mist’. Studies evaluated included randomized controlled trials, effectiveness and indirect protection studies. This review demonstrates that LAIV has considerable efficacy and effectiveness in school-age children.

Keywords:

• effectiveness
• efficacy
• influenza vaccine
• live attenuated influenza vaccine
• school-age children

Financial & competing interests disclosure

This study was sponsored by MedImmune. R Olajide is an employee of AstraZeneca, the parent company of MedImmune. K Coelingh and P MacDonald are former employees of MedImmune. R Yogev is on the speakers bureau for MedImmune. The authors thank C Ambrose and H Caspard (MedImmune) for review of the manuscript and helpful comments and D Swanson (AstraZeneca) for assistance with manuscript preparation. Medical writing assistance, including developing a first draft based on an outline developed by the authors, editing and formatting the manuscript, and collating and incorporating the authors’ comments, was provided by AS Wu, JE Fincke and C Lundin of Complete Healthcare Communications, Inc. (Chadds Ford, PA) and funded by AstraZeneca. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key issues

• Vaccine policy bodies in several countries have recently made preferential recommendations for live attenuated influenza vaccine (LAIV) versus inactivated influenza vaccine (IIV) in children 2–6 or 2–17 years of age. These recommendations were based on prelicensure clinical trials of LAIV that demonstrated high absolute efficacy against influenza and higher relative efficacy compared with IIV.

• Differing policy recommendations reflect, in part, differing views on whether sufficient comparative efficacy data for LAIV versus IIV are available for children older than 6 years of age.

• Efficacy data from randomized controlled trials for LAIV in school-age children are limited.

• Our review of available randomized controlled trials suggests that the efficacy of LAIV in school-age children was 96% against influenza B; no statistically significant efficacy data were available for influenza A strains due to low circulation of A strains in the study season. Relative efficacy of LAIV compared with IIV was 35% (statistically significant) against all influenza strains in a season dominated by influenza B.

• LAIV effectiveness in school-age children against medically attended laboratory-confirmed influenza illness ranged from 60 to 82% in case–control studies in seasons dominated by A/H1N1pdm09 and A/H3N2 strains.

• Direct effectiveness in school-age children (i.e., either vaccinated children or the age group targeted for vaccination) against laboratory-confirmed influenza illness ranged from 37 to 79% in community intervention studies. In addition, vaccination of school-age children indirectly protected young adults in their community against MAARI.

• LAIV direct effectiveness against laboratory-confirmed influenza illness ranged from 51 to 67% in school programs. In addition, significant direct effectiveness against absenteeism was consistently demonstrated. Vaccination of school-age children also indirectly protected their households and adult and elderly community members against influenza illness and absenteeism.

• Additional studies assessing the effectiveness of the quadrivalent formulation of LAIV in younger and older children are ongoing.

Notes