Even healthy people can get very sick from influenza (flu) and can spread it to others. The U.S. Centers for Disease Control and Prevention estimates that flu-related hospitalizations since 2010 have ranged from 140,000 to 710,000 annually, while flu-related deaths have ranged from 12,000 to 56,000. During flu season, flu viruses circulate at higher levels in the U.S. population. (“Flu season” in the U.S. can begin as early as October and last as late as May.)
Getting an annual flu vaccine is the best way to reduce your risk of getting sick with flu and spreading it to others. When more people get vaccinated against flu, it spreads less easily through a community. Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine.
The flu vaccine is given annually and it changes slightly from year to year. The vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season. While it may not protect against all strains of influenza, it can lessen the severity of the infection by preparing the immune system for a similar strain.
Source: U.S. Centers for Disease Control and Prevention