People should start getting vaccinated for seasonal flu in September and October, but they can get vaccinated as late as "December, January and beyond," according to the CDC.
No vaccine is 100 percent effective, but it's the best protection against flu and can prevent many illnesses and deaths, the FDA said.
People need to get vaccinated each year because the strains of circulating flu differ each year. Every year, experts from the FDA, the CDC, the World Health Organization and elsewhere collect flu virus samples from around the world to identify strains that may cause the most illness during the upcoming season.
Based on these forecasts and on the recommendations of the FDA's Vaccine and Related Products Advisory Committee, the agency determines the strains that should be included in vaccines for the U.S. population. The closer the match between the strains in the vaccine and those circulating, the better the protection against the flu.
It's possible the match between the vaccine and circulating virus is less than optimal. But even in years when the vaccine isn't a good match, a shot can reduce the severity of the flu if you catch it, and it may help prevent flu-related complications, according to the FDA.
Each year in the United States an estimated 5 percent to 20 percent of the population is stricken with the seasonal flu. More than 200,000 people are hospitalized and about 36,000 people die. Older people, young children, and people with chronic health problems are at higher risk for flu-related complications.
The FDA said the six vaccines for 2009-2010 and the manufacturers are: Afluria, CSL Limited; Fluarix, GlaxoSmithKline Biologicals; FluLaval, ID Biomedical Corporation; Fluvirin, Novartis
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