Not all is lost if you cannot get a flu shot.

Experts say a lesser-known vaccine pioneered by a University of Pennsylvania professor more than 30 years ago can help stave off serious complications of influenza and save lives.

Pneumovax 23 protects against a potentially fatal bacterial infection that can accompany influenza. While it is not a substitute for the flu vaccine, Pneumovax offers an important defense that many people overlook.

Available for a generation, Pneumovax remains underused, reaching only about half of its main target population – seniors – among the most vulnerable to the infection, according to government health experts.

Like other adult vaccines, Pneumovax often flies below the radar of doctors and patients. Physicians fail to offer it, patients do not know to ask about it, and health officials do not adequately publicize it.

Now, because of the current flu-vaccine shortage, public agencies from the U.S. Centers for Disease Control and Prevention to the Camden County, N.J., health department are stepping up their campaign for more widespread use of the pneumococcal vaccine.

“It is one of the things we can do now … to prevent some of the well-known complications of influenza,” said physician Anthony Fauci, director of the National Institute of Allergy and Infectious Disease.

Anticipating the demand, Merck & Co., the only maker of an adult pneumococcal vaccine in the United States, said it plans to triple its output this year to 18 million doses at its West Point, Pa., plant.

Pneumovax is just one strategy being promoted by health officials to reduce flu problems this year. The federal government said the nation had enough antiviral medicines on hand to prevent or treat influenza virus in more than 40 million people. Public health officials also are encouraging basic personal hygiene, such as hand washing or covering a cough or sneeze, to reduce the spread of the flu.

Health officials announced last month the nation had lost about half its flu vaccine supply. Chiron Corp., one of two major vaccine producers, announced it would not be providing 48 million doses because of quality problems at its British plant. Since then, government officials have scrambled to locate additional supplies, both in the United States and abroad. Aventis Pasteur, the other major U.S. supplier, plans to provide almost 90 percent of the anticipated 66 million doses available this year.

The nation’s supply still will fall well below the 98 million expected before the shortage.

Pneumovax has been designed to protect people against a bacterium, called pneumococcus, that can lead to pneumonia, bloodstream infections and meningitis. It causes an estimated 40,000 deaths a year. Research suggests it accounts for a large number of the estimated 8,000 influenza-related pneumonia deaths each year.

Neil Fishman, director of health-care epidemiology at the University of Pennsylvania Medical Center, said Pneumovax should be a particularly useful tool during this year’s flu season. “It is a very safe vaccine and well tolerated,” he said. “There is very little downside.”

He said pneumonia was the most common and serious complication of influenza. And Pneumovax prevents the most common type of pneumonia.

But it is not a perfect shield. It prevents disease in about 60 percent to 75 percent of inoculated individuals, experts say.

While those figures may not look impressive, the vaccine protects against a spectrum of the most prevalent pneumococcal strains, combining 23 inoculations in a single injection. An individual may become immune to a number of strains, but not necessarily all.

“This is a good vaccine; it is moderately effective,” said Raymond Strikas, an associate director in the National Immunization Program.

His program recommends the vaccine for people 65 and older, those with chronic conditions and patients with low resistance to infection. It is aimed at nearly the same target group as the flu vaccine. And unlike the flu shot, which is given annually, a shot of Pneumovax can cover an adult for life.

Robert Austrian, the 88-year-old University of Pennsylvania professor emeritus who pioneered the vaccine, became intrigued with pneumonia while a medical student at Johns Hopkins in the 1930s. And he still spends five or six days a week huddled over a microscope in his Penn lab, assessing pneumococcal strains for the World Health Organization. He describes the bacterium as a beautiful and “fastidious organism.”

Austrian, a physician who has been much honored for his research, started out as a maverick in the 1950s, studying the bacterial infection when so many others considered the disease already treatable. Because antibiotics had become such a potent weapon against infections, many people believed the disease had largely disappeared. A vaccine developed during World War II was abandoned as unnecessary.

But Austrian found antibiotics did not cure everyone, and thousands of people still died from pneumococcal infections. Armed with the data, he finally secured grant money from the National Institutes of Health to pursue vaccine development in the late 1960s.

A few years later, he went to South Africa to test his vaccine in gold mines where pneumonia was rampant. He said the studies showed the pneumococcal vaccine of that era, which protected against 13 strains, reduced the number of pneumonia cases by half. And the presence of infection in patients’ blood fell by about 80 percent.

Austrian developed a vaccine using polysaccharides, or complex sugars, from the outer coating of the bacterial cells. Today’s adult vaccine relies on the same method. (Using some of that technology, Wyeth sells a new vaccine designed specifically for children under 24 months.)

“He is really an icon and very humble,” Fishman said. “He was the one in the late 1940s who went against the grain of medical thought and said this is a disease that needs to be dealt with.”

Still, only 56 percent of seniors have been vaccinated against pneumococcal disease – a far cry from the 90 percent goal set by public health officials by 2010.

“Traditionally as a society we have not done a great job administering vaccine to adults,” Fishman said.

There are a lot of reasons, he said, starting with a lack of public funding to push it.

Austrian said he believed the adult vaccine still was not more widely used because people do not like to receive an injection, or they are not aware of the potential risks for disease.

Frank Leone, a pulmonary professor at Thomas Jefferson University, said some people had the misconception the pneumonia vaccine, like the flu vaccine, would cause disease.

“We need to educate that it is safe and can’t cause illness,” he said. “It is something that health care needs to do a better job on.”