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For younger children, two doses of H1N1 vaccine may be necessary
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One dose of the influenza A (H1N1) vaccine should be sufficient for protection in adults, but a second dose may be necessary for children aged 9 years and younger, according to results of a new study published in The Lancet.
The study, conducted by French and American researchers, included four groups of participants: infants aged 6 to 35 months, children aged 3 to 9 years, adults aged 18 to 64 years, and adults aged 65 years and older. A total of 423 children and 750 adults were given the vaccine.
All study participants were randomly assigned placebo or influenza A (H1N1) vaccine containing a dose of haemagglutinin of 7.5 µg, 15 µg or 30 µg. (Only adults were given the 30 µg dose.)
Participants were assessed for immunogenicity on day 21. Among those participants who received the vaccine, seroprotection was seen in 45% to 50% of infants aged 6 to 35 months, in 69% to 75% of children aged 3 to 9 years, in 95% to 100% of adults aged 18 to 64 years, and in 93% to 95% of adults aged 65 years and older. The researchers said the high levels of seroprotection seen in adults indicates that one dose of influenza A (H1N1) should be sufficient for most patients. However, the lower rates seen in children indicate a second dose for younger patients may be necessary.
The researchers also said the safety and reactogenicity of the influenza A (H1N1) vaccine were acceptable and were similar to those of the seasonal vaccine.
Plennevaux E. The Lancet