4

CDC lists a death rate up to 1 in 500, but mentions that before the vaccine there were thought to be 3-4 million cases and 500 deaths each year, which would be a 1 in 6,000-8,000 death rate (Source:https://www.cdc.gov/vaccines/pubs/pinkbook/meas.html)

Also, case-fatality rate calculated by dividing the total number of cases from 1994 to 2014 (excluding 2005 due to missing data) by the total number of deaths for the same time period and rounding the result to the nearest ten gives 1 in 250.

Source for the number of cases and deaths: https://www.cdc.gov/vaccines/pubs/pinkbook/downloads/appendices/E/reported-cases.pdf