A substantial number of influenza-associated deaths occurred among U.S. children during the 2003-2004 influenza season. High priority should be given to improvements in influenza-vaccine coverage and improvements in the diagnosis and treatment of influenza to reduce childhood mortality from influenza.

A single 15-microg dose of 2009 H1N1 vaccine was immunogenic in adults, with mild-to-moderate vaccine-associated reactions. (ClinicalTrials.gov number, NCT00938639).

HE DISEASE BURDEN OF SEAsonal influenza in the pediatric population is generally attributed to a combination of immunologic naivety, prolonged virus shedding, and enhanced transmission opportunity in child-care and educational institutions. 1 Consistent with this experience, initial reports of the introduction and indigenous transmission of 2009 influenza A(H1N1) infection in many countries have largely involved children, 2 often attending day or boarding schools. [3][4][5] Serosurveys have demonstrated little or no cross-reactivity of the pediatric sera sample to the new virus strain, under-Context In the ongoing influenza pandemic, a safe and effective vaccine against 2009 influenza A(H1N1) is needed for infants and children.Objective To assess the immunogenicity and safety of a 2009 influenza A(H1N1) vaccine in children.Design, Setting, and Participants Randomized, observer-blind, age-stratified, parallel group study assessing 2 doses of an inactivated, split-virus 2009 influenza A(H1N1) vaccine in 370 healthy infants and children aged 6 months to less than 9 years living in Australia.Intervention Intramuscular injection of 15 µg or 30 µg of hemagglutinin antigen dose of monovalent, unadjuvanted 2009 influenza A(H1N1) vaccine in a 2-dose regimen, administered 21 days apart.Main Outcome Measures Hemagglutination inhibition assay to estimate the proportion of participants with antibody titers of 1:40 or greater, seroconversion, or a significant antibody titer increase, and factor increase in geometric mean titer. Assessments of solicited adverse events during 7 days and unsolicited adverse events for 21 days after each vaccination. ResultsFollowing the first dose of vaccine, antibody titers of 1:40 or greater were observed in 161 of 174 infants and children in the 15-µg group (92.5%; 95% confidence interval [CI], 87.6%-95.6%) and in 168 of 172 infants and children in the 30-µg group (97.7%; 95% CI, 94.2%-99.1%). Corresponding seroconversion rates were 86.8% (95% CI, 80.9%-91.0%) and 94.2% (95% CI, 89.6%-96.8%), and factor increases in geometric mean titer were 13.6 (95% CI,). All participants demonstrated antibody titers of 1:40 or greater after the second vaccine dose. Immune responses were robust regardless of age, baseline serostatus, or seasonal influenza vaccination status. The majority of adverse events were mild to moderate in severity. ConclusionOne 15-µg dose of vaccine was immunogenic in infants and children starting at 6 months of age and vaccine-associated reactions were mild to moderate in severity. Trial Registration clinicaltrials.gov Identifier: NCT00940108

ILIs were common among our study participants, accounting for a large portion of illness, work loss, and impaired work performance during the influenza season. Vaccination was associated with substantial health and productivity benefits. Vaccine delivery should be improved for this high-priority group.