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Australian study: Single dose of influenza A (H1N1) vaccine sufficient for adults

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A single dose of influenza A (H1N1) vaccine may be sufficient to protect against the virus in adults, according to findings from a new study by Australian researchers.

The study results, published yesterday in The New England Journal of Medicine, indicated that a single 15-µg dose of 2009 H1N1 vaccine offered protection. The results also indicated that the vaccine was associated with only mild-to-moderate adverse events.

These results are based on findings from an ongoing randomized, observer-blind, parallel-group study being conducted in Australia. The study is designed to examine two doses of an inactivated, split-virus 2009 H1N1 vaccine. All study includes 240 participants who are all healthy Australian adults aged between 18 and 64 years.

The participants were randomized to receive either 15 µg or 30 µg of hemagglutinin antigen by intramuscular injection. There were 120 patients in each group. Antibody titers were measured at baseline and again at 21 days following vaccination.

At day 21 following vaccination, results indicated that 116 of the participants in the 15-µg dose group and 112 of the participants in the 30-µg dose group had antibody titers of 1:40 or more.

“These results will help to inform pandemic planning, especially in light of widespread concern about vaccine availability because of low manufacturing yields,” the researchers wrote. “The high level of immune protection afforded by a single 15-µg dose should improve the coverage and logistics of mass H1N1 vaccination programs.”

In an editorial accompanying the study, University of Washington researcher Kathleen M. Neuzil, MD, MPH, wrote, “On the basis of these data, it would be appropriate to begin vaccination with the use of one dose of the usual antigen.”

Neuzil, who chairs the Advisory Committee on Immunization Practices’ influenza vaccine workgroup, added that children still may need two doses but added vaccine should not be held in reserve for a second dose. She wrote that immunogenicity data in children are needed.

Greenberg M, et al. N Engl J Med. 2009;doi:10.1056/NEJMoa0907413