Between June 1970 and January 1971, 633 cases of measles occurred in Texarkana, a city bisected by the Texas-Arkansas state line.
A total of 606 (95.7%) of the cases occurred in Texarkana (Bowie County), Tex, a community that had never had a measles vaccination campaign. The level of prior immunity, natural plus vaccine-induced, in the 11,185 children aged 1 to 9 years in Bowie County was estimated to be 57%. Only 27 cases occurred in Texarkana (Miller County), Ark, where more than 95% of the 6,016 children aged 1 to 9 years were immune. Nineteen of the 27 Arkansas patients had documented exposures in Texas.
Twenty-seven cases of measles occurred in previously vaccinated children. Six of these children had received vaccine with measles immune globulin prior to 1 year of age. Vaccine efficacy was calculated to be 95.9%.
Landrigan PJ. Epidemic Measles in a Divided City. JAMA. 1972;221(6):567-570. doi:10.1001/jama.1972.03200190013003