Safety, immunogenicity and efficacy of influenza vaccine in children.

OBJECTIVES To review the immunogenicity, safety and efficacy of inactivated and attenuated trivalent influenza vaccines in children. SOURCES OF DATA Database search of the medical literature indexed on MEDLINE, LILACS and in the Cochrane Library. Review articles, clinical trials and epidemiological studies published from 1990 to 2006 were selected for analysis. SUMMARY OF THE FINDINGS Influenza is an infectious disease that is both universal and seasonal, with incidence in all age groups and annual epidemics characterized by excessive morbidity and mortality. The elderly and people with comorbidity are high risk groups for severe influenza. It has recently been proven that healthy infants suffer similar morbidity to other risk groups, and therefore vaccination against influenza is indicated for them too, as being the most effective means of preventing infection by the influenza virus. The safety of influenza vaccines in children appears adequate, with the most often observed adverse effects being local reactions or fever. Immunogenicity in children varies from 30 to 90%, being directly proportional to age. Efficacy depends on the primary objective and can range from levels comparable with placebo to up to 91% efficacy against confirmed influenza A infection. Schoolchildren play an important role in the dissemination of the influenza virus, and population studies have demonstrated herd immunity. CONCLUSIONS Trivalent influenza vaccines, whether inactivated or attenuated, have low reactogenicity and offer variable immunogenicity and efficacy in children. Vaccination is effective for prevention of infections by the influenza virus and for reducing morbidity. More powerful studies of efficacy and safety in infants are still required.