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Staph Vaccine Shines in Difficult Test

Cuts infection rate 57% in vulnerable kidney patients

WEDNESDAY, Feb. 13, 2002 (HealthDayNews) -- An experimental vaccine for one of the most aggressive bacterial infections has passed a major test, proving it can protect even patients with severely hobbled immune systems from the deadly illness.

The vaccine is the first to ward off so-called opportunistic pathogens, microbes that thrive in people with weakened immune function. Staphylococcus aureus is one of the worst, a usually drug-resistant bacterium that kills between 10 percent and 25 percent of the people it infects.

However, a study in tomorrow's issue of the New England Journal of Medicine finds the new vaccine, called StaphVax, cut the incidence of blood-borne staph infections by nearly 60 percent in patients with end-stage kidney disease. The vaccine also managed to provoke an immune response in 86 percent of these patients, who are extremely vulnerable to infections.

"The fact that it worked in this population is really remarkable," says Dr. John Robbins, a vaccine expert at the National Institute of Child Health and Human Development and a co-author of the journal article. Robbins, who helped shepherd the shot from its birth at Penn State University in the mid-1970s, says it would likely provide patients with stronger immune systems even more protection.

Staph infections are a common complication of frequent needle use and surgeries ranging from hip replacement to heart bypass. They also cause toxic shock syndrome. Studies have found staph is becoming more and more resistant to antibiotics -- even the most powerful one, vancomycin.

Robbins and a colleague, Dr. Rachel Schneerson, received the prestigious Pasteur and Lasker awards for their work on the vaccine for Haemophilus influenzae type B (Hib). Like that germ, S. aureus relies on a sugar-coated outer wall for safe passage through the body's defenses. Like the Hib vaccine, StaphVax belongs to a class of inoculations that use mimics of these long sugar molecules, or polysaccharides, to alert the immune system to this trick. In the case of StaphVax, the polysaccharides hitch a ride into the body on a harmless carrier protein plucked from a toxin of another microbe, Pseudomonas aeruginosa.

The vaccine, which is being developed commercially by Nabi Corp. of Boca Raton, Fla., stimulates antibodies -- sentinel proteins that warn the body's killer immune cells of an invasion -- to two strains of S. aureus, 5 and 8. Together, these types account for about 85 percent of staph infections.

In the latest study, researchers tested the injection in 1,804 patients with end-stage kidney disease. All were undergoing kidney dialysis to clean their blood of waste products, and had severely suppressed immune systems, the result of both their condition and the treatment for it.

About three-quarters of the patients stayed in the study for 54 weeks. Of those, roughly half were given a single dose of the vaccine and half received sham injections. By the end of the study, the researchers, say, staph infections occurred in 11 of 892 vaccinated patients versus 26 of the 906 who didn't get the therapy -- a 57 percent difference.

The shot triggered a sharp rise in antibodies to staph within about 10 days of being given, and remained effective for about 40 weeks. However, during the last three months of the study, the vaccine began losing its ability to prevent infection, and by the end of the trial it was no better than the dummy injection.

Still, Robert Naso, Nabi's senior vice president and a co-author of the study, says his company is "pretty enthusiastic about the response we got" in such a sick group of people. Naso thinks as many as 10 million patients a year could be eligible for the vaccine, most of whom would be far less ill than end-stage kidney failure patients.

Naso says it will be at least three years before the company seeks U.S. Food and Drug Administration approval for its staph vaccine. In the meantime, the company plans to repeat the latest trial to verify its results. It is also developing a purified antibody therapy to support the vaccine by boosting the immune system, as well as a vaccine to prevent the third most common form of S. aureus, type 336.

What To Do

To learn more about staph infections, try KidsHealth.

For a look at staph germs, check out the University of Wisconsin.

To find out more about hospital-acquired illnesses, visit the Centers for Disease Control and Prevention.

SOURCES: Interviews with John Robbins, M.D., chief, laboratory of developmental and molecular immunity, National Institute of Child Health and Human Development, Bethesda, Md.; Robert Naso, Ph.D., senior vice president, Nabi Corp., Boca Raton, Fla.; Feb. 14, 2002, New England Journal of Medicine
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