The<unk>  or flu shot is a vaccine to protect against the highly variable<unk>  virus.
The annual flu kills an estimated 36,000 people in the United States. The annually updated trivalent flu vaccine for the 2007–2008 season consists of hemagglutinin (HA) surface glycoprotein components from<unk>  H3N2, H1N1, and B<unk>  viruses.
Each year the<unk>  virus changes and different strains become dominant. Due to the high mutability of the virus a particular vaccine formulation usually works for only about a year. The World Health Organization coordinates the contents of the vaccine each year to contain the most likely strains of the virus to attack the next year. The flu vaccine is usually recommended for anyone in a high-risk group who would be likely to suffer complications from<unk> .
(intranasal)
Influenza vaccine
Caries vaccine
Polio vaccine
MMR vaccine
Traveller vaccination influenza
Childhood vaccination schedule
HIV vaccine
Hepatitis B vaccine