Researchers say just one dose of swine flu vaccine leads to a "strong immune response" according to a pilot study.
A total of 100 healthy volunteers were tested by scientists from the University of Leicester to see how their immune systems responded.
Some 80% of the volunteers showed a "strong, potentially protective" response after one dose, with more than 90% showing the same response after two doses, trial leader Dr Iain Stephenson found.
He said: "The results suggest that one vaccine dose may be sufficient to protect against A(H1N1) swine flu, rather than two.
"The aim of the trial was to find out how many doses and what type of vaccine is needed to give protection.
"These initial results should help to plan vaccination campaigns in the autumn, including doses and timings."
Dr Stephenson, from Leicester University's Department of Infection, Immunity and Inflammation, said of his study: "Results showed that the serum antibody responses were highest among subjects who received two doses of vaccine, however a single vaccine dose also induced responses associated with protection against influenza."