Federal health officials said on Thursday they were changing two of the three strains in this winter's influenza vaccine and lowering the age for which a flu shot is recommended.
The government's Advisory Committee on Immunization Practices recommended that people aged 50 years and older should receive the flu vaccine. Previously, the flu shot was recommended for adults 65 and older.
The committee said it was recommending the flu vaccine for people aged 50 to 65 because almost one-third of adults in that age group have one or more medical conditions that put them at high risk of flu-related hospitalization and death.
It said fewer than 40% of the 41 million people in that age group were vaccinated against influenza in 1997, the latest year for which information was available.
Health officials also recommended updating the virus designation to include new versions of two type A flu strains. The overwhelming majority of last winter's flu cases were type A.
The winter 2000-2001 flu vaccine will include types A/Moscow and A/New Caledonia, two strains first identified in 1999. They will replace the A/Beijing and A/Sydney strains included in the 1999-2000 flu vaccine.
The Centers for Disease Control and Prevention (CDC) said the B/Beijing strain included in last year's vaccine would also be part of this winter's shot.
The CDC said 20,000 to 40,000 people die from flu outbreaks every year. The agency said last winter's flu season was no worse than the previous five winters, in terms of severity and timing.
The flu vaccine is changed every year to reflect the strains that researchers expect to circulate. The influenza vaccine licensed in the United States is made from killed influenza viruses, which cannot cause infection.
