The U.S. Centers for Disease Control and Prevention has approved three antiviral drugs as a means of “preventing” the flu. Although not to be taken as substitutes for the flu vaccine during this season’s shortage, amantadine, rimantadine and oseltamivir have been approved for flu prevention.

An ample supply of these prescription drugs exists, according to Health and Human Services Secretary Tommy Thompson. Patients take the drugs for five days to prevent infection from the influenza virus but not other illnesses associated with it, such as the common cold.

Antiviral drugs are most often used in conjunction with flu vaccines in institutional settings such as nursing homes to control flu outbreaks. Experts recommend that people in nursing homes and others in the high-risk category take antiviral drugs in the event that they cannot obtain a flu vaccine.

The U.S. is currently experiencing a flu vaccine shortage due to the license of the manufacturer of half the expected supply being taken away because of poor quality.