I never make this stuff up.
The campaign produced a sustained improvement in compliance with hand hygiene, coinciding with a reduction of nosocomial infections and MRSA transmission. The promotion of bedside, antiseptic handrubs largely contributed to the increase in compliance.
www.thelancet.com
Pittet et al. "Effectiveness of a hospital-wide programme to improve compliance with hand hygiene"
After implementing a very aggressive handwashing program across an entire hospital system, MRSA infections came down from 2 per 10,000 patient days to 1 per 10,000 days. This technically is a 50% decline in the rate but you can see its a tiny absolute risk reduction. Handwashing liquid used per day increased by 5x fold across the hospital system with a reduction in infection by that much. Staph infections are actually the best disease I think to track for handwashing effectiveness because its directly transmitted by physical contact. Some other studies look at things like respiratory infections and blood stream infections which are more murky because contact isn't necessarily how those things develop.