Centers for Disease Control Recommendations for 2009
People who should get vaccinated each year are:
According to the Centers for Disease Control (CDC), the only type of influenza vaccine that has been licensed in the United States to the present time is made from killed influenza viruses, which CANNOT cause infection. Less than 1/3 of those who receive vaccine have some soreness at the vaccination site and about 5-10% experience mild side effects, such as headache or low-grade fever for about one day after vaccination. These side effects are most likely to occur in children who have not been exposed to influenza virus in the past.
Vaccine efficacy varies from one person to another. Studies of healthy, young adults have shown influenza vaccine to be 70%-90% effective in preventing illness.
Although only a few different influenza viruses circulate at any given time, people continue to get ill with the flu throughout their lives. The reason is that the viruses are continually changing, usually as a result of mutation in the viral genes. The vaccine contains killed viruses representing three different strains. Each year the vaccine is updated to include the most current influenza virus strains and it is suggested that individuals get their shot every year.
The flu season typically peaks from January through March. Vaccine supply for this fall is sufficient to vaccinate the "at risk" population as well as healthy individuals.