"We'll probably be looking at that in a few weeks in case we don't get as good a response with the unadjuvanted vaccine," Fauci said. "We don't plan to start any trials on adjuvants at least until we get a bit into the adjuvanted trials."
He said that a mild flu season would likely mean the trials of a vaccine with an adjuvant would not get started. But a swine flu that returned quickly and spread quickly might force their usage.
"It's something that we're keeping as a contingency in case we need to use them," Fauci said. "Right now, the main priority is to test the unadjuvanted vaccine."
Should an adjuvant be needed, however, Fauci said there is little question that it would be safe.
"We're more cautious than when we use something that we've used every year for decades," he said, noting, however, "the Europeans have used these same adjuvants for a long period of time with a … reasonable safety record."
But if adjuvants were to be used, they would likely be used in older people, where they have been tested, rather than children.
"There's not a lot of data on adjuvants in young kids -- even from the Europeans," Fauci said.
Officials do not expect a shortage of swine flu vaccine. "We don't anticipate that we will run out, but it's possible," Fauci said.
But while Americans may not face a shortage, Fedson said that not using adjuvants is a problem from an international perspective, although it makes getting the vaccine approved in the United States easier.
"From the regulator point of view, this will be the least onerous pathway to follow to get it approved," he said. "I think that's the path of easy regulatory approval, but whether it meets the public health needs of the world and the nation is another matter."
The problem, he said, is that the concerns for approval are for the individual. But even if the United States has enough, failure to use adjuvants means that doses for developing countries -- who don't have their own vaccine production capacity -- are unavailable.
Even more, said Fedson, because the swine flu virus has not been experienced by many Americans, they will need two doses of vaccine instead of one to develop immunity.
Describing the distribution methods for swine flu vaccine "a boutique approach to global public health," Fedson called them "an approach which will not make much difference for the people in 90 percent of the world, who will not have access to vaccines or antivirals."