The first clinical trial data on new vaccines being developed to treat the H1N1 pandemic flu virus in the U.S. suggest that one dose will work to immunize most people, according to a preliminary report in the New England Journal of Medicine. Researchers studied two vaccines, one which had a substance added to improve immune response, called an adjuvant , and one that didn’t, for 21 days. Both showed the vaccines elicted immune responses with single shot. One big question for public health officials was whether a single dose would be sufficient. Full results will be published after patients have been followed for 42 days, the journal said. An accompanying editorial, written by Kathleen Neuzil of the University of Washington, calls the findings “welcome

and reassuring” and suggests that it would be “appropriate” to start vaccination using one regular dose of non-adjuvanted vaccine. Two doses might be needed in children, she writes, but if supplies are short, the vaccine shouldn’t be held in reserve to give a second dose. The nonadjuvant vaccine is being developed by CSL Ltd. of Australia. The adjuvant version is from Novartis. Both are expected to be available in the fall. Side effects, including pain at the injection site and headaches, were reasonably tolerated, Neuzil noted. Chinese vaccine marker Sinovac Biotech and Novartis have both said recently that their swine-flu vaccines showed positive results.

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Swine Flu Update: A Single-Dose Vaccine Appears to Work, Study Shows