The Food and Drug Administration approved the ordinary seasonal flu vaccine on Monday and said Americans should plan to be vaccinated.

Vaccines against seasonal flu usually become available in September or October and flu experts say it is worthwhile to be immunized as late as January, as the U.S. influenza season usually peaks in February.

This year will be different -- the new H1N1 swine flu virus has circulated all summer and companies are working to make a separate vaccine against the pandemic strain.

The seasonal influenza vaccine will not protect against the 2009 H1N1 influenza virus that resulted in the declaration of a pandemic by the World Health Organization on June 11, 2009, the FDA said in a statement.

Although this year's seasonal vaccine is directed against other strains of influenza expected to be circulating and will not provide protection against the 2009 H1N1 influenza virus, it is still important for those Americans for whom it is recommended to receive the seasonal influenza vaccine.

The U.S. government says a swine flu vaccine should be available by mid-October and it likely will be offered to younger adults and older children, with healthcare workers first in line so they can stay healthy to vaccinate everyone else.

Six companies make seasonal flu vaccine for the U.S. market: GlaxoSmithKline Plc and ID Biomedical Corp, Novartis AG, Sanofi-Aventis SA and AstraZeneca, through its MedImmune unit, and CSL Ltd.

The seasonal flu vaccine includes three strains of the most common circulating flu viruses.

Between 5 percent and 20 percent of the U.S. population develops influenza each year. More than 200,000 are hospitalized from its complications and about 36,000 people die -- with 250,000 to 500,000 deaths globally.

The new pandemic strain is believed to have infected millions of people.

Medicine