Analysis of adverse events following immunization in Minas Gerais, Brazil, 2011: a cross-sectional study.

Objective: to analyze the main adverse events occurring following immunization in Minas Gerais State, Brazil, in 2011.
Methods: this is a cross-sectional study using secondary data from the Brazilian Information System on Adverse Events Following Immunization.
Results: 1,449 adverse events were found; more than half occurred in children under one year of age (56.1%; OR=1.39; 95%CI: 1.08;1.78); the highest rates per 100,000 doses administered were found in the Southern Triangle (36.3), Northwest (25.7) and Southern (22.7) areas of the state; tetravalent vaccine had the highest reactogenicity (46.1%) and hypotonic-hyporesponsive episode was the most frequent event (15.9%); events were significantly associated with inactivated vaccines (OR=4.08; 95%CI: 3.51;4.75); most of the reported events were closed as 'undefined' (58.9%).
Conclusion: events were found in all regions of Minas Gerais state and were most frequent following administration of inactivated vaccines and among children under one year of age.