This underlying bias is consistent with the findings of decreased rates of respiratory events among LAIV recipients relative to TIV-vaccinated controls that remained after adjusting for multiple comparisons. It also appears likely that despite matching there were underlying differences between LAIV recipients and unvaccinated controls, with unvaccinated controls being less likely to access vaccination and healthcare in general. This could explain the increased rate of events

related to routine preventive care in LAIV recipients compared with those unvaccinated, such as well visits, vision disorder (a combination of codes including myopia, hyperopia, and other routine visual disorders), ATM Kinase Inhibitor acne, obesity, nail disorder, and congenital anomaly (given the age of our study population this code represented pre-existing congenital anomalies, not those in the offspring of a study subject). A selection bias for or against LAIV in individuals with certain medical conditions could result in an apparent increased or decreased rate of the condition in LAIV recipients

compared with controls. This phenomenon explains the decreased rates of pregnancy-related events among LAIV recipients; there is a warning against the use of LAIV in pregnant women. Similarly, the increased rates of some psychiatric and behavioral disorders such as attention deficit disorder/attention deficit hyperactivity disorder and depression among LAIV recipients 9–17 years of age appear to be the EGFR inhibitor result of individuals with those conditions selecting LAIV because of its intranasal administration or its lack of thimerosal and other preservatives. This selection bias

has been observed in analyses of children receiving LAIV versus TIV in a large, national private insurance claims database, MarketScan® Research Data (Thomson Reuters, New York, NY, USA). below Other notable findings were those related to influenza. The lower rates of influenza in children 5–8 years of age within 42 days of vaccination compared with those unvaccinated or vaccinated with TIV are likely a result of the efficacy of LAIV and high rate of medically attended influenza illness in this age group. Among those 9–17 years of age, there was an increase in influenza within 21 days of vaccination in the within-cohort analysis. This could be due to lower vaccine efficacy in the period immediately following vaccination, while protective immune responses are still developing, or due to exposure to wild-type influenza at the time of vaccination. Additionally, it could be due to individuals with other respiratory illnesses being diagnosed with influenza owing to detection of LAIV vaccine strains by point-of-care testing.