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| |  One Dose of H1N1 Vaccine May Protect Children, But 2 Doses Still Recommended CHICAGO -- December 21, 2009 -- One dose of the influenza A(H1N1) vaccine may be effective to protect infants and children and reduce transmission of the H1N1 virus, according to a study published early online and appearing in the January 6 print issue of JAMA. “The Advisory Committee on Immunization Practices currently recommends that infants and children aged 9 years or younger receive 2 doses of H1N1 vaccine at least 21 days apart, based on existing experience with seasonal trivalent influenza vaccines in this age group,” the authors wrote. Terry Nolan, PhD, University of Melbourne, Melbourne, Australia, and colleagues assessed the effectiveness and safety of 2 doses of an H1N1 vaccine in 370 healthy infants and children aged 6 months to less than 9 years living in Australia. The children were randomised into groups that received a 2-injection regimen 21 days apart in doses of either 15-mcg or 30-mcg of the vaccine. “Following the first dose of vaccine, antibody titers of 1:40 or greater were observed in 161 of 174 infants and children in the 15-mcg group (92.5%) and in 168 of 172 infants and children in the 30 mcg group (97.7%),” the authors reported. “All participants demonstrated antibody titers of 1:40 or greater after the second vaccine dose.” The researchers noted that the majority of adverse reactions to the vaccine were mild to moderate in severity. The immune responses to the vaccine were strong regardless of age, baseline antibody status, or whether the child had received a seasonal influenza vaccination prior to this study. “Our findings suggest that a single dose 15-mcg dose vaccine regimen may be effective and well tolerated in children, and may have positive implications for disease protection and reduced transmission of pandemic H1N1 in the wider population,” the authors concluded. In an accompanying editorial, Anthony E. Fiore, MD, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, and Kathleen M. Neuzil, M.D, of PATH, Seattle, Washington wrote that children have been a primary source of illness in community outbreaks of pandemic influenza with more severe complications, hospitalizations, and deaths from this virus than what is usually seen for seasonal influenza. The editorial authors urge caution at interpretation of the results of the study. “The hemagglutinin antigen content administered to 6-month-old infants and children younger than 3 years in this study was 15-mcg, the equivalent of 2 doses of the 7.5-mcg vaccine currently licensed in the United States for this age group.” “The immunogenicity data presented by Nolan et al suggest that at least some children will be protected after a single 15-mcg dose of the H1N1 vaccine used in this study, but the findings cannot be generalised with confidence to all children, epidemiological circumstances in every country, or different vaccine formulations.” The authors of the study concluded that “it remains prudent to continue to follow current recommendations for administering 2 doses to infants and young children while awaiting definitive vaccine effectiveness data.”
SOURCE: JAMA
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