The symptoms may resemble those of a nasty cold -- headache, fever, sore throat -- but as any flu sufferer knows, they are much more vicious. Unlike a cold, the flu produces a sensation of having been run over by a Mack truck.

So, many people are beginning to ask if it's worth getting a flu shot. Health officials suggest one only for people in certain high-risk groups.

This year, the Centers for Disease Control (CDC) in Atlanta predicts a return of the same three influenza viruses that circulated in the United States last year -- A-Taiwan, A-Leningrad and B-Ann Arbor. The flu season extends from September to March with a peak in January and February.

"We are not predicting a major change in the flu this season," said Dr. Steven R. Mostow, assistant chairman of the Department of Medicine at Rose Medical Center in Denver and a member of the National Influenza Advisory Board.

As a result, many people will still have a resistance, and doctors hope the flu season will be relatively mild. But even though no new major strains have developed, flu viruses of the same strain constantly change into new forms, causing people to get the flu more than once.

Flu viruses "mutate frequently," said CDC epidemiologist Nancy Arden, "so that the antibody formed because of infection with a prior strain no longer recognizes the changes in the new virus."

So new flu vaccines, which are made out of "inactive," or dead, viruses, must be developed every year to keep up with the changes.

Influenza kills 10,000 Americans in a non-epidemic year and 50,000 in an epidemic year, Rose Medical Center's Mostow said. He attributes a lot of this to the low numbers of people getting vaccinated. Of the 45 to 50 million people in high-risk groups, only an estimated 20 percent get flu shots.

"It drives me nuts that we have a preventable illness that is not being prevented," Mostow said.

Public health guidelines on who should get a flu shot are aimed at protecting those at risk of dying because they develop complications. Those who should be vaccinated include: :: People of any age with chronic heart or lung disease and residents of chronic care facilities. :: Healthy people 65 and older and people of any age with a metabolic disease such as diabetes, asthma, severe forms of anemia or a suppressed immune system. The shot is also recommended for children and teen-agers with kidney disease. :: Children and teens on chronic aspirin therapy. This is because taking aspirin during the flu can lead to Reye syndrome, a condition that causes liver and brain damage. (Children with the flu should be given Tylenol or other acetaminophin pill to ease symptoms.) :: People who work in nursing homes and neonatal care centers who are likely to transmit the virus to others. It is also advised for families with a household member in a high-risk group living at home, such as a grandmother with heart disease.

For young, healthy people, getting the shot is a matter of choice, CDC's Arden said. "The chance of a healthy younger person having a life-threatening complication following the flu is relatively low."

But the flu is a real nuisance. And in a bad year, 20 to 30 percent of the population can be affected, Arden said. She estimates that the flu costs $3 billion to $5 billion a year, including the cost of nonprescription drugs, medical care, hospitalization and loss of time from work.

So why don't people, particularly those in high-risk groups, get vaccinated?

One reason, said Mostow, is because people don't believe the vaccine works. "It prevents influenza in 70 percent of the people who get it and it modifies the disease {people get a milder case} in the other 30 percent."

So even though it works well seven times in 10, there are still a lot of people who get the shot and also get the flu, leading to widespread doubt of its effectiveness.

Another reason is that people think the shot hurts. The vaccine is prepared in a preloaded syringe and the needles are small, Mostow said. "Some 20 percent of people will have a sore arm the next day, but they can still play golf or tennis."

A misconception that the vaccine actually causes the flu has also contributed to an avoidance of the shot. This is based on people's experience with earlier vaccines, Arden said. Vaccines developed in the 1940s were very crude, causing reactions that mimicked flu symptoms, she said.

Today, about 5 to 10 percent of people may have a mild fever response to the vaccine and some degree of headache or muscle ache.

People also think a flu shot will prevent colds and this is simply not so, Mostow said. It only helps prevent influenza.

The flu virus was isolated in 1934 and since then, epidemics have taken place in 1957, 1968 and 1977. Researchers believe that flu viruses originate in animals. The viruses are found in aquatic birds, said Dr. Robert G. Webster, director of WHO's Collaborating Laboratory on Influenza in Lower Animals, and the theory is that they pass from ducks and pigs to humans. "We think this is why these events occur in China, because the main food supply is ducks and pigs."

Few people get the vaccine, Moscow theorizes, because of a lack of public education and a failure by doctors to push the vaccine. "A lot of doctors don't have a system to identify high-risk patients," he said.

Flu shots cost about $15 in a doctor's office and are also available at public clinics.