All analyses were performed using SAS® statistical software, Version 9.1.3 or higher (SAS Institute Inc., Cary, NC, USA). During the 2007–2008 and 2008–2009 seasons (seasons 1 and 2), LAIV vaccination rates in those aged <24 months and those 24–59 months with asthma or immunocompromise were low relative to the general population of children 24–59 months (Table 1). However, the rate of vaccination in those with wheezing was comparable with that in the general population of children in this age group. In all cohorts and in the general population, vaccination rates with TIV were higher than with LAIV. From season 1 to season 2, the rate
of LAIV use in the general population increased 4.5-fold, whereas 3-MA use in the cohorts of interest, with the exception of the immunocompromised group, increased 2.8–3.3-fold. The rate of use
of TIV in all cohorts and within the general population changed little from season 1 to season 2 (Table 1). Among children younger than 2 years, those with a claim for LAIV in season 1 numbered 138 in total, and 42 were aged <6 months; in season 2, those with a claim for LAIV numbered 537 in total, and 84 were aged <6 months. A detailed claims analysis was performed for each subject younger than 6 months, an age for which no influenza vaccine is indicated. In 116 of 126 subjects,
a claim for LAIV vaccination occurred during a visit in which 1 or more routine childhood vaccinations were given in accordance with the Sorafenib American Academy of Pediatrics recommended vaccination schedule. No other trends were observed. Among children identified with wheezing, the frequency of SABA and ICS use were generally similar most among LAIV and TIV recipients in both study seasons (Supplementary Table 1). Among children with asthma, however, there was a trend toward fewer LAIV recipients compared with TIV recipients having ICS dispensed in the past 12 months (year 1, 52% vs. 61%; year 2, 46% vs. 60%; LAIV vs. TIV, respectively). As would be expected, the proportion with ICS use was lower in children with wheezing compared with those with asthma in both study seasons. Among vaccinated children in the immunocompromised cohort, at the time of vaccination more than half were classified as immunocompromised owing to recent receipt of systemic corticosteroids (SCS). Of the 101 LAIV-vaccinated children in this cohort during the 2 seasons, 57 were included owing to a claim for SCS, 34 were included because of a claim for an immunodeficiency, 7 were included owing to a claim for another immunosuppressing medication, and 3 were included for a malignancy.