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.
Even with the news that only one dose may be needed to confer immunity, some infectious disease experts were still cautious in their optimism.
"This is potentially good news," said Dr. John Bartlett, chair of the Infectious Disease Society of America's Task Force on Antimicrobial Availability.
"Generally, I think the results are good news," agreed Dr. John Treanor, a professor of infectious diseases at the University of Rochester Medical Center in Rochester, N.Y. "There will be additional information from other ongoing studies which should be available soon and which will hopefully confirm these conclusions. But the overall impression I think is that for adults, a single dose of vaccine will be sufficient."
Others, however, described the findings as a major coup.
"This is obviously huge, because, one, the total amount of vaccine produced goes twice as far, and two, you don't have to immunize everyone twice, which will increase coverage tremendously," said Dr. George Rutherford, director of the University of California San Francisco Institute for Global Health.
And Robert Field, professor of Health Management and Policy at the Drexel University School of Public Health in Philadelphia, said that a single-dose vaccine is important for logistical reasons, as well.
"It is dramatically easier to administer one shot than two," Field said. "With a two-dose regimen, many people will neglect to get the second shot. ... For instance, if someone gets the first one at a supermarket, do they have to return there, can they get it at another supermarket, can they go to their physician's office, or can they go elsewhere?"
The trials, however, involved only adult subjects. Rutherford said that while the jury is still out on the studies in children, the outcome could be different for this group of vaccine recipients.
"The big loose end is children," he said. "They will likely still have to receive two doses, just like with the current seasonal vaccine."
But Treanor said that here may still be a chance that many pediatric patients, too, may be able to get by with one dose. He noted that the results from the trials are similar to what might be seen with a seasonal flu vaccine, at least in adults.
"If you could extrapolate, you would guess that it will turn out that kids [ages] 9 to 18 will also only need a single dose, but that really remains to be determined," he said.
Likewise, Dr. Christopher Ohl, associate professor of medicine at the Wake Forest University School of Medicine in Winston-Salem, N.C., said that it remains to be seen whether adults with weaker immune systems will need two doses of the vaccine.
"[It] will be important to see how one dose does in young children and immunocompromised adults, two groups were vaccination is especially important," he said.