The best protection from the flu is to receive the annual flu vaccine. While the vaccine will not guarantee you will not get the flu, it lessens the severity and duration of illness in most of those who do become ill.
In 2010, the US Advisory Committee on Immunization Practices expanded the recommendation for influenza vaccination to include all individuals 6 months of age and older. High risk individuals, their close contacts, and healthcare workers remain high priority populations to receive flu vaccination.
The influenza virus has a high rate of mutation and immunity from infection or vaccination does not confer long lasting protection. Because inactivated vaccines take approximately 6 months to manufacture, each year’s flu vaccine is comprised of the predominant flu strains from the previous year. The protective efficacy of the influenza vaccine is determined by how well the predicted influenza strains of the vaccine “match” the circulating strains of virus circulating during the flu season. The influenza vaccine provides up to 80% protection in healthy individuals when the vaccine is a good “match”. The influenza vaccine is less effective in the population groups that are most susceptible to complications of the flu (the young, the elderly, and persons with weakened immune systems due to chronic illness). More recent literature estimates of the efficacy of the flu vaccine at about 62% (this number includes the healthy population as well as the elderly, the young, and the immunocompromised).
Contrary to popular myth, the flu vaccine cannot cause the flu. The most common adverse effect is mild arm soreness at the injection site. The immune response to the flu vaccine can often cause a low grade fever and mild systemic symptoms for 8 to 24 hours, which can be mistaken for an infection. Protective antibodies usually appear 2 weeks after the flu vaccine.