But because most healthy adults will recover from a flu infection without complications, doctors have tended to provide antiviral therapy only to those at greatest risk, such as people with other illnesses or immune system weakness, as well as the elderly and young children.
Some evidence exists, however, that the swine flu virus circulating in Mexico may target the group traditionally thought safest: healthy young or middle-aged adults.
Despite the questions, the CDC has already issued what it calls "interim guidance" for the use of the medications. The guidelines, which the agency says may change as the outbreak evolves, state that antiviral medications are:
* Recommended for an ill person suspected to have swine influenza A (H1N1).
* Recommended as a preventive measure for people at high risk for complications from flu who have close contacts with a confirmed or suspected case; schoolchildren at high risk for complications who have had close contact with a confirmed or suspected case; travelers to Mexico at high risk for complications; border workers in Mexico who are at high risk for complications; and healthcare workers or public health workers who have had unprotected close contact with a person ill from swine flu.
* Considered for any healthcare worker at high risk for complications who is working in an area with confirmed swine flu cases and caring for patients with acute febrile respiratory disease; non-high-risk people who are traveling to Mexico; and first responders or border workers working in areas with confirmed cases.
Details on the length of treatment and other information are available on the CDC's swine flu website.
The Food and Drug Administration on Monday issued an emergency declaration authorizing certain broader uses of antiviral medications. For example, the order allows for prescribing Relenza and Tamiflu in young children, even though the labeling for the drugs calls for use only in children 7 years and older for treatment and 5 years and older for prevention. Tamiflu is used only in children 1 year or older.
The outbreak is already too extensive for health officials to use the antiviral drugs in the way that would have been best, Flaherty said.
"The hope was that [health officials] could target an area to contain an emergency pandemic flu by providing prophylaxis for an area," he said. "But this virus is already beyond containing. It's been seen in so many states that that really isn't going to be possible."