The US Health officials announced that they have approved six versions of the influenza vaccine for 2008-2009 with new strains of the virus likely to spread. With the change in viruses, every season’s vaccines are altered to give better protection. The FDA, the U.S. Centers for Disease Control and Prevention, the World Health Organization and other institutions studied differing virus samples over the period of a year from around the world. Based on that, the FDA selected the three strains the drug manufacturers need to include in the vaccines for Americans. Officials said, the better the match between the circulating virus and the vaccines, the better the protection will be.

Every year the FDA updates the vaccines and one or two strains out of the three are updated, two strains from Type A, an H1N1 and an H3N2 version, and one for Type B. This year however all three strains have been changed and two out of the three strains included in the vaccines for the United States this year are now in use for the Southern Hemisphere's currently ongoing 2008 flu season.

Dr. Jesse L. Goodman, director of FDA's Center for Biologics Evaluation and Research, said, "One of the biggest challenges in the fight against influenza is producing new vaccines every year. There is no other instance where new vaccines must be made every year."

The vaccines that have been cleared by the U.S. Food and Drug Administration this year include GlaxoSmithKline Plc's Fluarix and FluLaval; Novartis AG's Fluvirin; Sanofi Aventis SA's Fluzone and CSL Ltd's Afluria and MedImmune, the FluMist nasal spray flu vaccine made by AstraZeneca Plc unit.

The vaccines for the years 2007-2008 proved to be ineffective as the strains that circulated were different to what was anticipated making it the worst flu season in the last four years, Dr. Dan Jernigan, deputy director of CDC's Influenza Division, said during a teleconference. "In the last 20 seasons, 16 have had good matches, and there have been four that were less than optimal matches," he said. Experts however feel that even if the vaccines and the circulating strains aren't an exact match, the vaccines will provide some protection and may reduce the severity of the illness or prevent flu-related complications.

The Centers for Disease Control and Prevention says influenza outbreaks can start as early as October and continue through till May and it estimates that every year 5-20% of the population gets the flu, more than 200,000 people are hospitalized due to flu complications and 36,000 people die from the flu. Older people, young children as well as people with health conditions are at a high risk for serious flu related complications.