Influenza (flu) is a common illness caused by infection with influenza A or influenza B virus. It can keep people from their usual activities for days to weeks and can also lead to complications, such as pneumonia or death, especially in people who are elderly or who have underlying medical conditions. Yearly flu vaccine (flu shot) prevents influenza and its complications. Treating flu involves rest, fluids, and medications to decrease fever and aches. However, two classes of antiflu drugs, if taken shortly after symptoms begin, can shorten illness by 1 or 2 days and may decrease complications. Antiflu drugs include older, cheaper drugs (amantadine and rimantadine) and newer, more expensive drugs (oseltamivir and zanamivir). The newer drugs are active against both types of flu virus, while the older ones treat only influenza A virus. A 5-day supply costs about $2 to $20 for the older drugs and $48 to $60 for the newer drugs. The drugs have side effects (including nausea, dizziness, or confusion). There are tests for flu, but they are not available everywhere. This means that doctors often need to start treatment without first testing to be sure that the symptoms are from flu. Previous studies show that the costs of the antiflu medications are worth the benefits in younger adults, but the cost-effectiveness of flu testing or using antiflu drugs in people older than 65 years of age is unknown.