I’ve found several historical accounts of the incidence and mortality from measles in the USA. Most of this is pre-vaccine and is attributed to general better health: nutrition, sanitation, less over-crowding.
This graph is from the American Journal of Public Health, 1980.
There are 3 numbers to keep track of
1) the incidence of measles in the population (also called the number of cases / 100,000 population)
2) the case-fatality ratio (what percentage of those with the disease die from that disease) and
3) Disease mortality rate (number of people who die of the disease in the population–deaths per 100,000 population).
The mortality rate in the USA from measles fell from 100 per million in 1912, down to ~1 per million in 1965 — all pre-vaccine. (The mid 1960s is the time when the measles vaccine was being introduced.) This drop is due to generally better health and better supportive medical care. Higher socioeconomic status and city/suburban locations did better than poor rural locations.
The vaccine itself is probably responsible for dropping that mortality down another big notch to 0.1 per million by 1975, as the number of cases dropped with the introduction of the vaccine (not shown well in this truncated figure).
General improvements in health and socioeconomic status are strongly correlated with lower measles mortality. For example, in a poor “third world” setting, mortality rates are almost 60-80 times higher than in developed nations.
Supportive medica care, like IV fluids for vomiting and dehydration, and antibiotics for secondary bacterial pneumonia also reduce the case fatality ratio and overall mortality.
A similar graph on an analog scale. Below 1 in 1 million is given as zero on this scale. This projection emphasize that credit for declining measles mortality cannot be all attributed to the vaccine.
Currently, the CDC advises that about 250 measles cases per year occur in the USA, almost all of which are imported by travelers.
With a case fatality ratio currently in the USA of 1 in 10,000, this lets us predicts that in the USA there will be ONE measles death and TWO cases of measles encephalopathy every 40 years.
It is a shocking conclusion: Right now in the USA, the disease is safer than the vaccine!