U.S. health regulators have approved six versions of the influenza vaccine to help combat the virus during the 2008-2009 flu season later this year.
The vaccines include GlaxoSmithKline Plc's Fluarix and FluLaval; Novartis AG's Fluvirin; Sanofi Aventis SA's Fluzone and CSL Ltd's Afluria, the U.S. Food and Drug Administration said on Tuesday.
The FDA also cleared the FluMist nasal spray flu vaccine made by AstraZeneca Plc unit MedImmune.
Each vaccine contains the same three strains of the influenza virus, which experts choose every year after weighing which ones are most likely to break out. Experts include two strains from Type A, an H1N1 and an H3N2 version, and one for Type B.
Outbreaks of the influenza virus can start as early as October and last through May, according to the Centers for Disease Control and Prevention.
Earlier this year, the FDA chose to update the vaccine with three new strains rather than only one or two as it usually does.
Vaccines for this past 2007-2008 flu season appeared largely ineffective in part because different strains than expected began circulating, experts have said. Still, a record 140 million doses were provided, the CDC has said.
Both Sanofi Aventis and MedImmune have already begun shipping their products.
MedImmune said earlier this week it plans to make 12 million doses of its nasal mist vaccine, which is approved for those ages 2 to 49.
Sanofi, which made 40 percent of last year's U.S. supply, last week said it had begun shipping an initial 1.3 million doses of its vaccine, which is approved for those at least 6 months old. It plans to double its U.S. capacity for the 2009- 2010 season.
In past years, the United States has experienced flu vaccine shortages when just three companies made the shots. In 2004, a contamination at then-flu vaccine maker Chiron Corp prevented roughly one-half of the U.S. flu vaccine supply from hitting the market. Novartis now owns Chiron.