Age limit does not replace serologic testing for determination of immune status for measles.

TL;DR: Adults more than 40 years old are not necessarily immune to measles, but a measles outbreak that involved healthcare workers occurred after contact with a 44-year-old patient revealed that 117 of 2,600 individuals tested seronegative for measles were more than40 years old.

Abstract: Adults more than 40 years old are not necessarily immune to measles. A measles outbreak that involved healthcare workers occurred after contact with a 44-year-old patient. Results of a hospital-wide program of mass screening revealed that 117 (4.5%) of 2,600 individuals tested seronegative for measles; 31 (26.1%) of these 117 individuals were more than 40 years old.