Single dose of H1N1 vaccine immunogenic in infants and children

January 01, 0001

Single dose of H1N1 vaccine immunogenic in infants and children

Currently, most bodies are recommending two doses of H1N1 vaccine in children age 6 months to 9 years based in part on previous experience with trivalent vaccine. These Australian researchers assessed the immunogenicity and safety of a 2009 influenza A(H1N1) vaccine in children through a randomized, observer-blinded group study assessing 2 doses of an inactivated, split-virus 2009 influenza A(H1N1) vaccine in 370 healthy infants and children in the above mentioned age range. Intramuscular injection of 15 µg or 30 µg were administered 21 days apart. The main outcome was a hemagglutination inhibition assay to estimate the proportion of participants with antibody titers of 1 to 40 or greater, seroconversion, or a significant antibody titer increase, and factor increase in geometric mean titer. Adverse events were also monitored.

They found: “Following the first dose of vaccine, antibody titers of 1 to 40 or greater were observed in 161 of 174 infants and children in the 15-µg group (92.5%) and in 168 of 172 infants and children in the 30-µg group (97.7%). Corresponding seroconversion rates were 86.8% and 94.2%, and factor increases in geometric mean titer were 13.6 and 18.3. All participants demonstrated antibody titers of 1 to40 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.”

The authors concluded: “One 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.”