WHICH INFLUENZA VACCINE IS FAVORED IN 2 TO 8 YEAR OLDS? A COST-EFFECTIVENESS ANALYSIS

Purpose: Meta-analyses conducted prior to widespread childhood vaccination found the intranasal live attenuated influenza vaccine (LAIV) more effective than the injectable inactivated influenza vaccine (IIV) in 2-8-year-olds, leading CDC in 2014 to state a preference for LAIV use in this age group. However, more recently, LAIV has not proven superior, and may be inferior, leading CDC in 2015 to rescind their LAIV preference statement. Here we explore circumstances where LAIV use would be clinically and economically favorable over IIV among children 2-8 years old.

Methods: A Markov model was used to estimate vaccination strategy cost-effectiveness in 2-8-year-old children, in terms of cost per quality adjusted life year (QALY) loss avoided. Input parameters were derived from CDC data, national databases, and medical literature sources. Vaccination and influenza rates were 5-year US monthly averages. Base case assumptions were: equal vaccine uptake, IIV use when LAIV was not indicated (in 11.7% of the cohort), and no indirect vaccination effects. Sensitivity analyses included estimates of indirect effects from both equation-based and agent-based models. Two-way sensitivity analyses, varying LAIV and IIV effectiveness and using a cost-savings threshold, were performed to examine LAIV and IIV effectiveness values favoring one vaccine over the other.

Results: Using prior effectiveness data in 2-8 year olds (LAIV 83%, IIV 64%), preferred LAIV use was less costly and more effective than IIV (dominant), with results sensitive only to LAIV and IIV effectiveness variation. Using 2014-15 US effectiveness data (LAIV 0%, IIV 15%), IIV is dominant. In 2-way sensitivity analyses (Figure), with the absolute effectiveness difference for LAIV to be favored increasing as IIV effectiveness increases, LAIV use was cost saving over the entire range of IIV effectiveness (0-81%) when absolute LAIV effectiveness was >7.1% higher than IIV, but never cost saving when absolute LAIV effectiveness was <3.5% higher than IIV. If IIV effectiveness in 2-8 year-olds remains 15%, then LAIV was not favored unless its effectiveness was >19.1%; if IIV effectiveness returns to 64%, LAIV effectiveness would have to be >70.3%.

Conclusion: In light of recent influenza vaccine effectiveness, our results support CDC's decision to no longer prefer LAIV use and provide guidance on effectiveness differences between vaccines that might lead to preferential recommendation of LAIV for 2-8 year olds.

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