One Dose, Not Two, May Do for Swine Flu Vaccine

Sept. 10, 2009— -- Infectious disease experts expressed relief in light of new research released Thursday suggesting that one dose of a new vaccine against the H1N1 swine flu may be enough to grant immunity for most people against the pandemic strain.

The two studies -- one out of Australia, the other out of the United States -- come less than a month after U.S. health officials predicted that delays in production could mean that less than a third of the 160 million doses of the vaccine initially predicted would be available by the planned rollout in mid-October.

"This is very exciting news," said Dr. Richard Besser, ABC News' senior health and medical editor and a former acting director of the CDC. "It has many implications. It could double the number of adults who could be vaccinated. It will greatly simplify vaccination programs by no longer needing to track people between the first and second dose. It will greatly reduce the costs of vaccination programs. It will increase the number of people willing to be vaccinated."

The new vaccine has been in development only since May. The first human trials of a candidate vaccine began in Australia in late July.

The race to develop the vaccine met with a major hurdle early on when developers were plagued with manufacturing and packaging delays, as well as a slow-growing "seed" strain of the virus needed to make the vaccine. The delay forced U.S. health officials to downgrade estimates of how many doses of the vaccine would be available in time for a mid-October rollout. The initial prediction of 160 million doses slipped to 120 million in July. By August, this estimate dipped further to just 45 million doses.