Among elderly nursing home residents, flu vaccine is most effective in preventing severe illness, secondary complications, and deaths. As long as flu vaccine is available, and flu activity is continuing, it is appropriate for persons at high-risk for serious complications from influenza to receive flu vaccine. Each year, influenza viruses are collected by many laboratories throughout the world, including the United States. This information, along with epidemiologic information on flu activity, is summarized and presented to an advisory committee of the Food and Drug Administration and at a WHO meeting. Usually one or two virus strains change in the vaccine each year.
Flu is merely a nuisance.
The licensed flu vaccine used in the United States, which is made from inactivated or killed influenza viruses, cannot cause influenza infection and does not cause influenza illness. When the vaccine viruses and circulating viruses are well matched, vaccine can be very effective. There are several different reasons for this belief. People who have received flu vaccine may subsequently develop a respiratory illness that is due to another virus but is mistaken for flu. In the elderly and those with certain chronic medical conditions, the vaccine is often less effective in preventing illness.