Asthma is the most common chronic medical condition in children. Prior observational studies of live attenuated influenza vaccine (LAIV) safety in asthmatic children have been limited due to confounding by indication, with LAIV restricted to patients with mild asthma. To minimize bias, we evaluated safety of LAIV in children with asthma using a natural experiment in which two medical groups, within a single health system, serving similar populations, differed in vaccination guidelines. Prior to 2010 both groups recommended inactivated influenza vaccine (IIV). Starting in 2010, one group recommended LAIV for children with asthma.
Methods: Asthmatic children age 2-18 years with visits to two large medical groups in the upper Midwest from 2007-2015 were identified and classified by severity and control using validated algorithms. Primary outcomes were lower respiratory events (LRE) occurring within 21 and 42 days after influenza immunization. Multiple records per subject were included when children received influenza vaccines in more than one season. The analysis was intention to treat with each medical group’s subjects analyzed as a group. A pre/post ratio of ratios (ROR) approach was used to estimate the LAIV guideline impact using a generalized linear model with a Poisson distribution, accounting for multiple records per subject and adjusting for age and asthma classification. Analyses were for the overall population, and stratified by age group: 2-4 and 5-18 years.
7959 observations from 4824 unique asthmatic children were analyzed, with1896 from the IIV guideline and 6061 from the LAIV guideline medical groups. Post-implementation, 67% received LAIV. Age and asthma classification adjusted ROR showed no increase in LREs using the LAIV guideline: overall ROR (95%CI): 0.79 (0.46-1.37) for LRE 21 days and 0.82 (.56-1.20) for 42 days; age 2-4: 1.07 (0.40-2.83) for 21 days and 1.0 (0.53-1.90) for 42 days; and age 5-18: 0.72 (0.37- 1.41) for 21 days and 0.75 (0.46-1.21) for 42 days.
A guideline recommending LAIV rather than IIV for asthmatic children did not result in more LREs following vaccination in children age 2-18. Guidelines for influenza vaccination in asthmatic children should be based on effectiveness studies.
A. Olsen, None
L. Kuckler, None
E. Kharbanda, None