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One Dose of H1N1 Vaccine Enough for Young

One dose of vaccine may be effective to protect infants and children and reduce transmission of the H1N1 virus, according to a study published by the Journal of the American Medical Association.

The story, to appear in the Journal's January 6 print edition, was published today online.

Researchers at the University of Melbourne, Australia and colleagues assessed the effectiveness and safety of receiving two doses of a 2009 influenza A (H1N1) vaccine.

The test groups were comprised of 370 healthy infants and children (aged 6 months to under nine years) who received a two-injection regimen three weeks apart. Doses were 15-micrograms or 30-micrograms.

The findings showed that a single 15-microgram dose may be effective, as most subjects had enough antibody levels after one dose to have sufficient protection against the H1N1 virus.

Of the subjects who received the 15-microgram dose, 92.5 percent were protected; in the group receiving a 30-microgram dose, 97.7 percent were protected.

The immune responses were strong despite differences in the subjects' ages, baseline antibody status, or whether a seasonal influenza vaccination had been administered prior to the study.

The researchers also noted that adverse reactions to the vaccine were mostly mild to moderate.

The Centers for Disease Control and Protection's Advisory Committee on Immunization Practices currently recommends infants and children between the ages of six months and nine years receive two doses of H1N1 influenza vaccine.

However, the smallest dosage size in the Australia study is twice the size of the vaccine dosages currently administered in the United States to children age six months to three years; they receive two 7.5-microgram doses of vaccine.

For more info:
Journal of the American Medical Association
2009 H1N1 Recommendations (CDC)