National health officials promise that they have enough flu vaccine to protect people from the dominant strains of the disease that are expected to hit this fall and winter.

Julie I. Gerberding, director of the Centers for Disease Control and Prevention, said that 143 million to 146 million doses of influenza vaccine should be available nationwide. Many flu shot clinics in Western Pennsylvania open Wednesday.

As usual, the vaccine contains three strains of flu. This year, there are two Type A Brisbane strains and one Type B Florida strain.

Daniel B. Jernigan, deputy director of the CDC influenza division, said in contrast to last year at this time, there is no indication that the three strains used to make up the vaccine supply will not be the strains that hit the United States.

"We are optimistic that this year's vaccine will be on target," he said, adding that the effectiveness depends on the immune status, health and age of the person receiving the vaccine, and whether the vaccine matches the virus in circulation.

"The closer the match, the more effective," Dr. Jernigan said. "In the last 20 years, we had good matches in 16 years. Last year we had only a partial match; two out of three [strains in the vaccine] did not have vaccine effectiveness."

With new CDC recommendations issued in March that all children, except those under 6 months of age, receive the vaccine, a larger supply than ever is needed. Demand for the vaccine is far below the number of people who are at risk from influenza.

Dr. Gerberding said there are 261 million people who should be vaccinated. In addition to children 6 months to 18 years old, they are: adults over 50, anyone with chronic illnesses such as heart disease or diabetes or compromised immune systems, pregnant women, and healthy people who have contact with those vulnerable people.

Even with the CDC recommendations, many of these people do not get the vaccine, from a majority of health care workers, 60 percent, to a sizable portion of adults over 65 about 30 percent, Dr. Gerberding said.

"There are still 36,000 deaths and 200,000 hospitalizations each year," she said.

She said older children, even those without health issues, need the vaccine because of the time they spend in school, susceptible to catching and spreading the virus.

The addition of healthy children adds about 30 million more people who need the vaccine, Dr. Gerberding said. Children under 6 months have a limited ability to develop immunity; children under 9 years old will need two doses of vaccine, four weeks apart.

Renee R. Jenkins, president of the American Academy of Pediatrics, emphasized the need for the vaccination of children:

"Up to a third of all children will become affected this year; approximately 100 children will die," she said. In the 2007-08 season, 86 children died -- including some otherwise healthy children.

"Children are highly susceptible, they're two to three times more likely than adults to get sick from influenza," Dr. Jenkins said, adding that the academy's projection may underestimate the effect on children this year.

"We urge parents and health care professionals to vaccinate all children through the entire season," she said.

Dr. Jenkins said that one in five children has a chronic disease, such as asthma or diabetes, and they need to be vaccinated, as well as people who come into contact with them.

There's still room for improvement in vaccinating the elderly, said Kerry Weems, acting administrator for the Centers for Medicare and Medicaid Services. People on Medicare can get a flu shot and pneumonia vaccine for free, at doctor's offices, hospitals, nursing homes, health departments, pharmacies and visiting nurse associations.

"Free should be cheap enough," he said. "Sadly, in any given state, 27 percent are not getting the vaccine."

A recent survey by the National Foundation for Infectious Diseases found that doctors need to talk more with their patients about the importance of flu vaccines, according to Ardis D. Hoven, infectious disease specialist and member of the American Medical Association board of trustees.

"The flu vaccine has been around for more than 50 years, but thousands still die from the virus. Our patients need to hear from us about the importance of [vaccination]," Dr. Hoven said.

"Patients don't ask questions; they think their health care provider would bring it up if they thought it was important. ... The vaccine is the best way to protect yourself and your family from the flu."

The vaccination rate of health care workers themselves is too low, Dr. Hoven said. "Health care professionals are the front line in the yearly battle against the flu. ... Getting the vaccine protects their patients and their loved ones."

Issuing a challenge to hospitals to improve their vaccination rates to 43 percent or above is the nonprofit Joint Commission Resources, an affiliate of the Joint Commission, which accredits and certifies health care organizations and programs in the United States. Details of the challenge can be found at the Web site www.fluvaccinationchallenge.com.

Allegheny General Hospital is joining that challenge, according to Cheryl Herbert, director of infection control. She said the vaccination rate of AGH employees matches the national average of 40 percent, but the drive is on to educate employees about the importance of getting their free vaccination.

"It's critical to vaccinate health care workers. Sometimes they feel they're invincible, they can't get sick," she said.

At the larger University of Pittsburgh Medical Center hospitals, where the rate is also in the 40 percent range, spokeswoman Amy Dugas Rose said there are roving carts delivering the free vaccine to employees as they work.

The Allegheny County Health Department flu shot clinic opens Oct. 20, while supplies last, at the ACHD office, 3441 Forbes Ave., Oakland. The shots will be $25 a dose for people not covered by Medicare. Pediatric thimerosal-free flu vaccine is also available, at $25 a dose. The nasal spray, its cost supported with a grant, will be $10. Clinic hours are: 9 a.m. to 3 p.m., Mondays, Tuesdays, Thursdays and Fridays 9 a.m. to 7 p.m. Wednesdays. No appointment is necessary.

Other flu shot clinics include those operated by the Health Hope Network (www.healthhopenetwork.org), Take Care Health (www.TakeCareHealth.com), and Minute Clinics (www.minuteclinic.com). Average cost of the flu shot is $24.99; the nasal spray is slightly higher.

For more information on influenza and vaccines for children, see AAP.org.