Trap-neuter-release programs for community cats help protect human health. That’s not just because altered cats are less likely to fight and roam, thus creating fewer opportunities for disease spread. It’s also because TNR programs routinely vaccinate their feline patients against rabies, a disease nearly always fatal to humans.
From the 2012 Maddie’s® Institute webcast Shelter Crowd Control: Keeping Community Cats Out of Shelters, given by Julie Levy, DVM, PhD, DACVIM, Director of Maddie's® Shelter Medicine Program at the University of Florida:
There are a number of papers that have been published to show that even a single vaccine given to a kitten or an adult cat is very likely to give them years of protection.
And we’ve also vaccinated cats in our program and then re-trapped them a couple months later to see how well they responded. ... (T)here was a very low proportion of cats that have protective antibodies against rabies before they were vaccinated, and when we re- trapped them a couple months later, 99 percent of the cats were protected against rabies. And that’s the same proportion that you would get from vaccinating pet animals.
Because we know even a single vaccine lasts for years, we think we’re promoting public health in a very dramatic way.
You can view Dr. Levy’s complete presentation here.