Babies, toddlers and the people who care for them are encouraged to get a shot starting in October. Other healthy people, including those aged 50 to 64, should get their shot beginning in November.

In the past, only young children at high risk for flu complications, such as those with chronic lung disorders, were recommended to get the vaccine. However, even generally healthy children aged 6 to 23 months are at increased risk for influenza-related hospitalizations, according to Harper,

In addition, health care workers, people at increased risk of developing influenza-related complications due to health conditions and household members of those at high risk should be vaccinated during October, the agency advises.

As in previous years, flu shots are strongly recommended for many people at high risk of complications. Such individuals include nursing home residents, adults and children with chronic heart or lung conditions, such as asthma, and those who need regular care due to chronic health problems such as diabetes, kidney disease or a weakened immune system. Women who will be more than 3 months pregnant during the flu season are also recommended to get the shot, according to the CDC.

"A lot of people think of influenza as a severe cold but, in fact, it is a potentially life-threatening infection and kills about 20,000 Americans every year and hospitalizes over 100,000 Americans every year," Harper said.

This season's flu vaccine has been matched to the three viral strains currently circulating around the world, CDC officials said at a press conference.

A yearly flu shot can prevent the onset of influenza during flu season, which in the United States lasts from the fall through the beginning of the following year. Each year, vaccine makers produce a new vaccine matched as closely as possible to the strains expected to be prevalent during the coming flu season. A vaccine well matched to circulating strains is more effective than one that is not.

While nobody knows exactly which influenza virus types will predominate or how severe the 2002-2003 flu season will be, "the optimal time to receive influenza vaccine" is during the months of October and November, according to the report in the October 4th issue of the Morbidity and Mortality Weekly Report.

The CDC tracks the types of influenza virus circulating in the US and worldwide annually in preparation for the upcoming influenza season. The data is gathered by the World Health Organization ( news - web sites) Collaborating Center for Surveillance, Epidemiology, and Control of Influenza at the CDC, which analyzes flu virus samples from laboratories around the world.

Currently, influenza A (H1), A (H3N2) and B viruses have circulated worldwide since May, and in North American only sporadic cases have been reported, the report indicates.

Harper said that the three US influenza vaccine manufacturers will distribute 80% of the 94 million doses by the end of October, and the remaining doses will likely be distributed in November and December.