A Postlicensure Evaluation of the Safety of Live Attenuated Influenza Vaccine in Children 2 to 4 Years of Age

Background:  Live attenuated influenza vaccine (LAIV) was initially approved for children aged ≥5 years and extended to children aged ≥2 years in 2007.

Objectives:  A postlicensure commitment was made to describe LAIV safety among eligible children 2-4 years of age.

Methods:  Eligible individuals received LAIV in Kaiser Permanente Northern California as part of routine care from October 2007 through March 2010 and were monitored afterwards using their healthcare database. Rates of medically attended events (MAEs) in LAIV recipients were compared with rates in 3 different nonrandomized controls; a self-control, unvaccinated controls, and TIV recipients. Subjects were matched for age and sex. All MAEs through 42 days postvaccination and all hospitalizations/deaths through 6 months postvaccination were analyzed. Statistical significance was assigned without multiplicity adjustment.

Results:  32,261 LAIV recipients were matched to 30,815 TIV recipients and 28,766 unvaccinated subjects. Of ~4000 rate comparisons, 83 and 221 occurred at a higher and lower rate, respectively, after vaccination with LAIV. Only urticaria within 21 days of vaccination occurred at a higher rate after LAIV in comparison with all 3 control groups. Among 82 asthma/wheezing comparisons, only 4 occurred at a higher rate after vaccination with LAIV in comparison with those unvaccinated. No anaphylaxis events occurred within 3 days postvaccination. Serious adverse events (SAEs) within 42 days of vaccination occurred in 32 LAIV recipients; only 3 events were considered possibly related to LAIV. No SAE occurred at a significantly higher rate among LAIV recipients. No deaths occurred among LAIV recipients throughout the study.

Conclusions:  In this postlicensure evaluation of LAIV safety in >30,000 children aged 2-4 years, there was no meaningful increase in adverse outcomes among eligible individuals who received LAIV, consistent with preapproval clinical studies and reports to the US Vaccine Adverse Events Reporting System following approval. Sponsored by MedImmune, LLC.