That's good news because they had thought it might take two to protect people from the new virus that is beginning to spread across the country.
Now, people will need a regular winter flu shot - already available - and a swine flu shot in October when that is ready. Originally there has been concern a total of three shots would be needed.
Australian shot maker CSL Ltd. published results of a study that found 75 percent to 96 percent of vaccinated people should be protected with one dose. U.S. data to be released Friday confirms those findings and shows the protection starts rapidly, lead U.S. scientist Dr. Anthony Fauci of the National Institutes of Health told The Associated Press.