Adverse events following vaccination against pandemic influenza A (H1N1) 2009 in children

The aim of this study was to estimate the frequency of adverse events following vaccination against pandemic influenza A (HIM) 2009 and associated factors in children from six months to two years of age (n = 156). Multivariate Cox regression was used to assess the independent associations between covariates and complaints of at least one adverse event. Strength of association was measured by hazard ratios and respective 95% confidence intervals. Following the first dose, 40.3% of parents reported one or more adverse events in their children, compared to 35.5% after the second dose. Systemic adverse events, specifically irritation, diarrhea, and fever, were more frequent than local reactions at the vaccination site. Incidence rates for adverse events in general and systemic reactions following the first dose were higher in children with concomitant illness or allergies (HR = 3.43, 95%CI: 1.34-8.77 and HR = 2.76, 95%CI: 1.11-6.89). Most events were mild. Cases of high fever, vomiting, and diarrhea prompted parents to seek care for their children at health services.