Staph infections remain a significant problem for hospital patients, and scientists are trying to develop vaccines to prevent Staphylococcus aureus bacteria from establishing itself in vital areas like the heart, lungs or blood. But it’s turning out to be a difficult task: A promising vaccine intended to protect heart-surgery patients from staph infections worked no better than a placebo, a new study reported.

Making matters worse, patients who developed staph infections despite getting the vaccine were more likely to die than infected patients who got the placebo, the study found.

The results, released Tuesday by the Journal of the American Medical Association, were from a double-blind, randomized, placebo-controlled trial involving about 8,000 patients in 26 countries. The vaccine, dubbed V710, had seemed to work well in animals. In human volunteers, a single dose produced antibodies, as intended. But the larger clinical trial was halted ahead of schedule, after safety monitors noticed that the vaccine didn’t protect patients better than the dummy shot when given under real-world conditions.

— Los Angeles Times