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One dose of swine flu vaccine may be enough

September 10, 2009 |  3:36 pm

Pig To the surprise of many scientists, preliminary results from a clinical trial of a new vaccine for pandemic H1N1 influenza conducted in Australia suggest that one dose of vaccine may be sufficient to provide protective antibodies, a finding that in effect doubles the number of vaccine doses that will be available, and greatly reduces the logistical problems associated with having to give two doses of the vaccine. The results, reported online today in the New England Journal of Medicine, confirm earlier results from China obtained with a similar vaccine. Unlike the Chinese vaccine, however, the Australian vaccine will be used in this country, accounting for about 20% of the U.S. supply.

Researchers had feared that two doses of swine flu vaccine would be required because most people younger than 65 have little or no residual immunity to swine-related viruses, so that a vaccination program would have to start from scratch. Seasonal flu vaccines, in contrast, work with only one dose because people have some residual immunity from exposure to other influenza viruses and vaccines. The sole exception is young children receiving their first dose of flu vaccine; they require two doses.

Dr. Michael E. Greenberg of Australia's CSL Ltd. and his colleagues studied the company's vaccine in 240 subjects, half younger than 50 and half 50 or older. Fully 95% of those who received a 15-microgram dose of antigen -- the standard dose that is used in seasonal flu vaccines -- developed a protective antibody response within 21 days after vaccination, and usually within eight to 10 days. No deaths or serious adverse events were observed -- only tenderness and pain at the injection site and some headaches.

Also in NEJM online, Dr. Tristan W. Clark of University Hospital Leicester in England and his colleagues reported on a separate study of a vaccine containing both 15 micrograms of antigen and an adjuvant, a chemical added to the vaccine to provoke a greater immune response. They found results similar to those reported by CSL. Their findings are of little relevance to the United States, however, because no flu vaccines containing adjuvants have been licensed in this country. They could be licensed on an emergency basis if there was a severe shortage of vaccine, however.

Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, told the Associated Press that U.S. results showing similar findings would be released Friday.

In other good news, MedImmune of Gaithersburg, Md., said it would ship as many as 5 million doses of its inhalable swine flu vaccine by the end of September. MedImmune researchers had found that the strain of virus it uses for its vaccine grows faster than that used by other manufacturers, speeding up the testing and manufacturing process. The vaccine, called FluMist, is not approved for use by pregnant women and people with underlying medical conditions.

-- Thomas H. Maugh II