WEDNESDAY, Dec. 16 (HealthDay News) -- A single 15-µg dose of vaccine provides H1N1 influenza protection in most individuals, though another dose can boost immune response in children and the elderly, according to the results of two studies in the Dec. 17 New England Journal of Medicine.

Michael E. Greenberg, M.D., of CSL in Parkville, Australia, and colleagues analyzed data from 240 Australians, aged 18 to 64 years, who were randomized to receive two doses of 15 or 30 µg of hemagglutinin antigen spaced 21 days apart. Most subjects (95 percent) who received the 15-µg dose had antibody titers of 1:40 or more by day 21 after the first dose. The authors did not note any serious adverse events, adverse events of special interest, or deaths.

Feng-Cai Zhu, M.D., of the Jiangsu Provincial Center for Disease Control and Prevention in Nanjing, China, and colleagues analyzed data from 2,200 Chinese subjects, aged 3 to 77 years. Subjects received two injections of placebo or vaccine spaced 21 days apart at doses ranging from 7.5 to 30 µg. By day 21, 97.1 percent of those aged 18 to 60 achieved a hemagglutinin-inhibition titer of 1:40 or more. However, this outcome was less common in children under 12 and adults over 60 (74.5 and 79.1 percent, respectively).

"The obvious advantage of a one-dose schedule is that, in the current time of vaccine scarcity, it doubles the number of people who may be vaccinated with a fixed amount of vaccine. Another clear advantage to the one-dose schedule is that antibody responses develop sooner," writes the author of an accompanying editorial.

In the first study, the authors were employees of CSL, which made the vaccine and supported the study. In the second study, several authors were employees of Hualan Biological Bacterin Company, which developed the vaccine and supported the study.

Abstract - Greenberg
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Abstract - Zhu
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