Antivirals are drugs that can treat people who have already been infected by a virus. They also can be used to prevent infection when given before or shortly after exposure and before illness occurs. They interfere with the life cycle of the influenza virus in the body and prevent it from multiplying thus preventing or lessening the infection. A key difference between a vaccine and antiviral drug is that the antiviral drug will prevent infection only when administered within a certain time frame before or after exposure and is effective during the time that the drug is being taken. A vaccine can be given long before exposure to the virus and can provide protection over a long period of time.
Vaccines are the best way to prevent disease. Flu vaccines are made from either pieces of the killed flu virus or weakened versions of the live virus that will not lead to disease. When vaccinated, the body's immune system makes antibodies which will fight off infection if exposure to the virus occurs.