Although it was successful in one late-stage trial, StaphVax, a vaccine in development to combat Staphylococcus aureus, failed to meet the primary end point in a second pivotal trial.
The vaccine's development is now on hold, perhaps indefinitely, according to Thomas H. McLain, president and CEO of Rockville, Md.-based Nabi Biopharmaceuticals.
StaphVax targets S. aureus types 5 and 8, eliciting antibodies to the bacteria's polysaccharide capsule, Mr. McLain said in an interview. The initial market would be people having elective invasive procedures.
In a randomized, double-blind, placebo-controlled study of 3,600 hemodialysis patients, there was no reduction in the incidence of infection with S. aureus types 5 and 8 compared with placebo.
The company issued only a press release in November; full data will likely be released after several months of analysis, Mr. McLain said. Meanwhile, the company withdrew its application for European Union approval and halted all development.
In the first phase III study, StaphVax induced partial immunity for 40 weeks in an end-stage renal disease population (N. Engl. J. Med. 2002;346:491–6).
Results also seemed to be promising in a recently completed substudy, according to its principal investigator, Dr. Todd K. Rosengart head of cardiothoracic surgery at Stony Brook University Hospital, N.Y. In that study, conducted when Dr. Rosengart was at Evanston Northwestern Healthcare, Ill., 120 patients undergoing elective, open cardiac surgery were given either the vaccine or a sham injection 7–40 days before the procedure. “We found dramatic increases in antibodies to types 5 and 8 S. aureus in 90% of our patients,” Dr. Rosengart said in an interview.
A vaccine is definitely needed, he noted, adding that although infections occur in only 1% of cases, the mortality rate with an infection is 5–10 times greater than for open heart surgery alone. “Infection is probably one of the greatest concerns for our patients,” he said.
Antibiotics, as well as screening and prevention programs, are starting to make a dent against S. aureus, but the bacteria—particularly the methicillin-resistant S. aureus (MRSA) strains that are on the rise—are still anathema to hospitals, surgeons, and patients. MRSA is one of the top 10 causes of death in the United States. About 126,000 people a year are infected with the resistant strain.
The bar for vaccine acceptance will be high, given the success of other S. aureus elimination techniques, said Dr. Lance Peterson, a colleague of Dr. Rosengart's at Evanston Northwestern. Patients at Evanston are tested for MRSA on admission and treated with a nasal antibiotic ointment for 5 days before a procedure in an effort to reduce postsurgical infections. The effort seems to be paying off so far, although there are data only from a pilot study in knee surgery.
The vaccine would need to be at least 75% effective, said Dr. Peterson, director of microbiology and infectious disease research at the Chicago-area health system. To be safe, the vaccine should not permanently destroy nasal carriage of S. aureus, he added.
Even if Nabi does not proceed with StaphVax's development, it is going forward with what Mr. McLain calls its next-generation approach—a vaccine that attacks the bacteria's cell walls. That investigation is in a phase I study.