A staph vaccine: How much would it help?

One more post on research from the meeting of the Society for Healthcare Epidemiology of America: Many MRSA researchers believe that the only way to truly control the pathogen — especially out in the community — will be through a vaccine.

Lay aside for the moment how problematic introducing a new vaccine can be these days, since the cost issues, along with shifts in the public's willingness to accept new vaccines, are ferocious hurdles. And lay aside also the difficulties that pharma companies have already faced in attempting to develop a staph vaccine.

But if such a vaccine were achieved, how many people could it help? Researchers from the Centers for Disease Control and Prevention attempted to answer that question in research presented at SHEA.

Background assumptions, part 1: The number of invasive MRSA infections now tops an estimated 105,000/year (a recalculation of the 94,000/year estimate from last October); more than 40% of invasive infections occur in those over 65; more than 50% are associated with a recent hospitalization; and 15% of MRSA infections recur at least once. And background assumptions part 2: A vaccine would have an efficacy rate of 40-75%, and an acceptance rate similar to flu-vaccine uptake: 20-50% among those 15-44, 35-70% among those 45-64, and 50-70% among those 65 and older.

Given those assumptions, Cynthia Lucero, MD and colleague predicted:

• If given only to those 65 and older, a vaccine would prevent from 12,720 to 32,270 invasive MRSA infections;
• If given to those over 65 and also those 15 and older who have already had an invasive infection, a vaccine would prevent 14,130 to 38,310 invasive MRSA infections;
• And if given to those over 65 and also anyone over 15 who is being discharged from a hospital, a vaccine would prevent from 17,240 to 49,940 invasive MRSA infections.

The best bang for the buck, the agency said, would be the middle strategy: It would prevent from 660 to 1,170 cases for every million doses of vaccine used. And since the vaccine would also cover methicillin-sensitive staph, it would likely prevent an equal number of serious MSSA cases as well.

The CDC is not by law allowed to lobby — or even, for the most part, allowed to offer a professional opinion unless Congress has asked it to do so. So these numbers are purely a thought experiment. But they're also a strong argument for the broad usefulness of a staph vaccine if one could be achieved.