a substantial portion of older americans may have some immunity to the swine-origin h1n1 influenza virus, a finding that may prove useful when and if a vaccine to the new flu strain becomes available. the questions of whom to target with a swine flu vaccine and how to stretch the supply if it is limited are among the most important issues facing public health officials over the next four months. scientists at the centers for disease control and prevention announced yesterday that a study using stored blood samples found that one-third of people older than 60 have antibodies that might protect them from infection with the new virus. if further research is able to better define who has partial immunity, those people might need only one dose of vaccine, not two.
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