The measles virus is one of the most infectious diseases known to man. A person with measles can cough in a room and leave, and hours later, if you’re unvaccinated, you could catch the virus from the droplets in the air the infected person left behind.
No other virus can do that.
For anyone born before 1960, there’s a good chance they suffered through a measles infection. They may have lived to tell about it, but they probably had friends who didn’t. In the US, before a vaccine was introduced in 1963, there were 4 million measles cases with 48,000 hospitalizations and 500 deaths in the US every year. Measles was also a leading killer of children globally.
The beauty of the vaccine is that most people who get the proper doses will never get sick with measles, even if they’re exposed. And by 2000, because of widespread vaccination, the virus was declared eliminated in the US: Enough people were immunized that outbreaks were uncommon, and deaths from measles were scarcely heard of.