So far, we’ve used vaccines to entirely wipe out two diseases: smallpox and rinderpest, which infects cattle.

We’ve also come extremely close to eradicating polio, with less than 500 new cases annually, largely in Afghanistan, Nigeria, and Pakistan.

In the United States, a long list of diseases have been nearly eradicated by vaccines: diphtheria, bacterial influenza, measles, mumps, rubella, and tetanus, among others.

Still, there are many developing countries that have limited vaccine supplies and scant funding for childhood vaccination services, which has allowed preventable diseases like whooping cough and rotavirus to continue spreading.

On the whole, though, the world has made progress: Global vaccination rates for measles, for example, climbed to 84 percent in 2013. UNICEF and the World Health Organization are always working to increase this number, focusing heavily on underdeveloped or developing countries with low vaccination rates.

The global vaccine coverage goals are crucial because diseases can’t infect or spread through vaccinated people — so if enough people are vaccinated, a pathogen won’t be able to find a new host and will eventually die off.