Briss PA, Fehrs LJ, Parker RA, Wright PF, Sannella EC, Hutcheson RH, Schaffner W. Division of Field Epidemiology, Centers for disease Control and Prevention, Atlanta, Georgia. Sustained Transmission Of mumps In A Highly Vaccinated Population: Assessment Of primary vaccine failure And Waning Vaccine-Induced Immunity. J Infect Dis. 1994 Jan;169(1):77-82.

From January to July 1991, an outbreak of mumps occurred in Maury County, Tennessee. At the primarily affected high school, where 98% of students and all but 1 student with mumps had been vaccinated before the outbreak, 68 mumps cases occurred among 1116 students (attack rate, 6.1%). Students vaccinated before 1988 (the first year mumps vaccination was required for school attendance in Tennessee) may have been at greater risk of mumps than those vaccinated later (65[6.1%] of 1001 vs. 2[2.2%] of 89; risk ratio, 2.9; 95% confidence interval, 0.7-11.6). Of 13 persons with confirmed mumps who underwent serologic testing, 3 lacked IgM antibody in well-timed acute- and convalescent-phase serum specimens. Vaccine failure accounted for a sustained mumps outbreak in a highly vaccinated population. Most mumps cases were attributable to primary vaccine failure. It is possible that waning vaccine-induced immunity also played a role.