Hull HF, Montes JM, Hays PC, Lucero RL. Risk factors for measles vaccine failure among immunized students. Pediatrics. 1985 Oct;76(4):518-23.

An outbreak of measles occurred in a municipal school system which had reported 98% of students immunized against measles. A case-control study was conducted to determine reasons for vaccine failure. Vaccine failure was associated with immunizations that could not be documented in the provider's records. Among children with provider-documented immunization, vaccine failure was associated with vaccination at 12 to 14 months of age with an odds ratio of 4.73. Among children vaccinated at 15 months or older, vaccine failure was not associated with time elapsed since vaccination. Studies should be conducted to determine whether unreliable immunization records are a more widespread problem. Further consideration should be given to routine revaccination of children previously vaccinated at 12 to 14 months of age.

We have here a 98% vaccinated population and vaccine failure occurred in those immunized at 12 to 14 months of age and 15 months and older. Time after vaccination was not a factor in vaccine failure.