Over the years, Robert Daum has learned to respect his adversary. In 1995, he and his co-workers at the University of Chicago children's hospital in Illinois were investigating infections that had affected two dozen children in their emergency department. Three children had fast-moving pneumonia. A fourth had an abscess the size of his fist buried in the muscle of one buttock. In a fifth, the bacterium had infiltrated the bones of one foot. The infections were resistant to many common antibiotics, including methicillin. To Daum's surprise, the culprit was MRSA — methicillin-resistant Staphylococcus aureus — a bacterium that was thought to spread only among hospital inpatients. But none of these kids had been to the hospital for months before becoming ill.

Few researchers were willing to accept the implications. Daum wrangled for 18 months with editors at the Journal of the American Medical Association over a paper reporting the cases and showing that this strain was dangerous, acquired in the community and differed genetically from hospital strains. His article was eventually published in 1998 and is now widely considered to be the early warning of an epidemic that currently results in millions of visits to doctors and hospitals a year.

Daum, a paediatric infectious-disease physician and founder of the University of Chicago's MRSA Research Center, is still raising the alarm about the epidemic. He sees the fight as more urgent than ever, and now thinks he knows how to win it. A few days before Christmas, he and Brad Spellberg, a physician who conducts vaccine research at the University of California, Los Angeles, published an article calling for a vaccine that would vanquish S. aureus. “We can't treat this,” Daum says. “We have to prevent it.”...