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Single H1N1 Vaccine Dose Likely Safe and Effective

Study finds 15 µg dose immunogenic in infants and children, with minimal side effects

MONDAY, Dec. 21 (HealthDay News) -- A single dose of influenza A(H1N1) vaccination is effective and safe in infants and children 6 months to less than 9 years of age, according to a study published online Dec. 21 in the Journal of the American Medical Association.

Terry Nolan, Ph.D., of the University of Melbourne in Australia, and colleagues assessed the immunogenicity and adverse event profile of two doses of an inactivated, spilt-virus 2009 H1N1 vaccine (15 µg and 30 µg) in 370 healthy infants and children. Immunogenicity was evaluated using a hemagglutination inhibition assay. Adverse events were evaluated at seven and 21 days after vaccination.

The researchers found that, after the first vaccine dose, antibody titers of 1:40 or greater were seen in 161 of 174 participants who received the 15 µg dose and in 168 of 172 individuals who received the 30 µg dose, with all patients reaching this end point upon receiving a second dose. The seroconversion rate after the first vaccine dose in the 15-µg group was 86.8 percent, while in the 30-µg group, the rate was 94.2 percent. Overall, associated adverse events were considered mild to moderate.

"Based on the immunogenicity data alone, a possible conclusion is that only one dose of the 2009 influenza A(H1N1) vaccine provides protection to a substantial proportion of previously unvaccinated children in some seasons," write the authors of an accompanying editorial.

The study was supported by CSL Ltd. Several authors reported financial associations with the company.

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