Seasonal Effectiveness of Live Attenuated and Inactivated Influenza Vaccine.

BACKGROUND Few observational studies have evaluated the relative effectiveness of live attenuated (LAIV) and inactivated (IIV) influenza vaccines against medically attended laboratory-confirmed influenza. METHODS We analyzed US Influenza Vaccine Effectiveness Network data from participants aged 2 to 17 years during 4 seasons (2010-2011 through 2013-2014) to compare relative effectiveness of LAIV and IIV against influenza-associated illness. Vaccine receipt was confirmed via provider/electronic medical records or immunization registry. We calculated the ratio (odds) of influenza-positive to influenza-negative participants among those age-appropriately vaccinated with either LAIV or IIV for the corresponding season. We examined relative effectiveness of LAIV and IIV by using adjusted odds ratios (ORs) and 95% confidence intervals (CIs) from logistic regression. RESULTS Of 6819 participants aged 2 to 17 years, 2703 were age-appropriately vaccinated with LAIV (n = 637) or IIV (n = 2066). Odds of influenza were similar for LAIV and IIV recipients during 3 seasons (2010-2011 through 2012-2013). In 2013-2014, odds of influenza were significantly higher among LAIV recipients compared with IIV recipients 2 to 8 years old (OR 5.36; 95% CI, 2.37 to 12.13). Participants vaccinated with LAIV or IIV had similar odds of illness associated with influenza A/H3N2 or B. LAIV recipients had greater odds of illness due to influenza A/H1N1pdm09 in 2010-2011 and 2013-2014. CONCLUSIONS We observed lower effectiveness of LAIV compared with IIV against influenza A/H1N1pdm09 but not A(H3N2) or B among children and adolescents, suggesting poor performance related to the LAIV A/H1N1pdm09 viral construct.