ABSTRACT
Vaccination has achieved significant and cost effective success in prevention of infectious disease. Although the current vaccines used are very effective and their side effects are minimal, generally no vaccine is not free from side effects. Incidence of adverse reactions after immunization may discourage people for further immunization of their children. The aim of this work was to determine the incidence of complications of vaccination in children and infants of Semnan, Iran. In a longitudinal study [prospective], all vaccinated children between September 2006 and March 2007 in 11 vaccination centers were studied. A specific questionnaire, including vaccine recipient profile, type of vaccine, birth weight, feeding and 46 adverse reactions were completed immediately after and 2,4,6,12, 18 months later. 5776 children were studied. 29% of the children showed at least one adverse reaction of vaccination. The most common adverse reactions were: fever [24%], pain at injection site [3.8%], swelling [2.5%], erythema [2.5%], induration [2.1%], and ulceration at injection site [2.1%]. Incidence of other complications was below 1%. The most dangerous complication of the vaccine was encephalitis [one case] and two cases had febrile seizures. The most cause of hospitalization was adverse reaction of MMR vaccine. Finally, of every four children, one child showed at least one complication that fever was the most common. In general, routine immunization program of Iran country against nine common infectious diseases has lower complications. This complication is mainly mild and transient and do not need any intervention by drugs. However, among these may be rare and dangerous complications such as seizures and encephalitis occur. Hence, a careful follow-up program is required to report complications of immunization