Information has been received from a published literature article and refers to a subject of unknown gender (aged 18-28). This report refers to a 20 year old subject enrolled in a not blinded other studies. The study population comprised patients of the private, multispeciality group practice with regional centers, the clinic maintained an electronic vaccination registry for immunizations administered by clinic providers, local public health agencies, and immunization providers. No measles cases were reported in the area during the study period. Two cohorts comprising 685 subjects were enrolled during 2009-2010. Cohort 1 (113 subjects) participated in a 10-year longitudinal study at the clinic examining immunogenicity and adverse events following the second MMR II vaccine dose (hereafter, "the longitudinal study"). To achieve adequate sample size, the clinic's vaccination registry was used to recruit subjects from cohort 2 for whom receipt of 2 MMR II doses was documented but who did not participate in the longitudinal study (572 subjects). Invitation letters were mailed to both cohorts, and follow-up telephone calls were made. Additionally, cohort 1 subjects who participated in the measles cell mediated immunity (CMI) substudy during the longitudinal study were asked to participate in the current CMI substudy. Although only 16 cohort 1 subjects (14.2%) had low or undetectable MeV antibody concentrations during the longitudinal study, 93 of 113 cohort 1 subjects had low or undetectable concentrations of antibody (defined previously) to at least one of the viruses targeted by MMR II during the longitudinal study, and all cohort 2 subjects were offered a third dose of MMR II. Serum was collected from all subjects immediately before (baseline) and 1 month and 1 year after MMR3 receipt. At each visit, subjects were questioned about measles occurrence, exposures, vaccinations, and other health events. MMR vaccine was administered during the initial visit. Informed consent was obtained from all subjects. Institutional review boards of the Clinic Research Foundation and the Centers for Disease Control and Prevention approved the study. Sample size determination and exclusion criteria were previously described. The 60 participants in the longitudinal measles CMI substudy or subjects with a low or undetectable MeV antibody concentration in greater then or equal to 1 serum specimen collected during the longitudinal study were asked to participate in the current CMI substudy. However, only 34 subjects (56.7%) meeting these criteria were re-enrolled. A convenience sample from cohort 2 was used to reach the recruitment goal of 60 subjects. Laboratory testing was performed at the end of the study. Other than each subject's unique identifier code and serum collection dates, laboratories were blinded to study information. Plaque Reduction Neutralization (PRN) Testing was performed using low-passage Edmonston MeV on Vero cell monolayers, as previously described. End points were determined for all serum samples tested, and 50% neutralizing doses were calculated using the Karber method. Serial 4-fold dilutions of serum were tested in duplicate starting at 1:8 and ending at 1:8192 against virus diluted to give 35-35 plaques/well and run in parallel with the Second WHO International Standard Reference Serum (66/202). After incubating the virus-serum mixtures at 337 degrees centigrade with 5% CO2, the mixtures were transferred onto corresponding 24-well tissue culture plates containing confluent Vero monolayers; after incubating for 1 hour at 37 degrees C, the inoculum was removed, and cells were overlaid with medium containing carboxy methylcellulose and returned to the incubator for 5 days prior to staining with neutral red and plaque counting. Serum samples from individual subjects were tested in the same assay run. Titers were standardized against the WHO reference serum, with a titer of 1:8 corresponding to 8 miU/mL in this assay. Cyropreserved peripheral blood mononuclear cells (PBMCs) were thawed and cultured overnight in 5% CO2 at 37 degrees C, medium supplemented with 4% human serum type AB (Lanza), 1% penicillin/streptomycin, an 1% 200 mM L-glutamine. Following the overnight culture, interferon gamma (IFN-gamma) production by T cells were assessed using enzyme-linked immunospot assays of PBMCs (5 x 10 ^5 cells/well), as previously described. PBMCs were stimulated either with a mixture of MeV hemagglutinin, fusion, and nucleoprotein proteins as 20-amino acid peptides (11 amino acids overlapping) at 1 microg/mL or with a lysate from MeV infected Vera cells at 10 microg/mL for 40 hours. RPMI medium and concanavalin A (5 microg/mL) were used as negative and positive controls, respectively. After stimulation, the plates were incubated with biotin-conjugated antibodies to human IFN-gamma and then developed and read, as previously described. Low and positive T-cell responses were categorized as <20 and greater than or equal to 20 spot-forming cells (SFCs)/million PBMCs, respectively. MeV IgG antibody avidity was evaluated to determine whether there was a correlation between neutralizing antibody concentrations and strength of antibody binding. After neutralization results were available, avidity testing was performed using the method described previously. Serum samples from all 662 subjects were split into quartiles based on baseline PRN antibody concentration. Subjects with undetectable neutralizing antibody concentrations were negative for MeV and IgG by the Captia Measles IgG enzyme immunoassay thus, avidity could not be measured. All subjects with low MeV neutralizing antibody concentrations at baseline, 1 month after MMR3 receipt, or 1 year of MMR3 receipt were tested for MeV antibody avidity. A random number generator selected specimens from at least 10 subjects from each of the remaining 3 quartiles for avidity testing; specimens from 59 subjects were evaluated. Each specimen was classified as negative if, at a 1:21 dilution, the Captia assay did not detect IgG and as having low avidity, if the end-titer avidity index (AI) was less than or equal to 30%; intermediate avidity, if the end-titer AI was greater than 30% less than 70% (intermediate results were retested); and high avidity, if the end-titer AI was greater than or equal to 70%. Based on previous studies, serum samples were categorized as negative for MeV neutralizing antibody (level, less then 8 miU/L), indicating susceptibility to infection and disease; having a low MeV neutralizing antibody level (121-900 miU/mL), indicating potential susceptibility to infection but not disease; and having a high MeV neutralizing antibody level (greater than 900 miU/mL), indicating nonsusceptibility to infection or disease. Serum samples were also dichotomized as indicating potential susceptibility (MeV neutralizing antibody level, less than 121 miU/mL) and nonsusceptibility (greater than or equal to 121 miU/mL). Cohorts 1 and 2 were combined during analysis because there were no statistically significant differences between the cohorts by sex, race/ethnicity, or age. However, cohort 1 had significantly lower geometric mean concentrations (GMCs) of MeV neutralizing antibody at baseline (P = .0289), so the reporters stratified the X2 risk factor analysis at 1 month and 1 year after MMR3 receipt by baseline MeV neutralizing antibody concentrations. Mental-Haenszel x2 and Fisher exact tests were performed to assess categorical variables. Wilcoxon rank sun tests were used for continuous variables. GMCs of MeV neutralizing antibody were calculated from base 2 log-transformed data. Statistical significance was assigned for P values of less than .05. Data were analyzed with SAS 9. Reverse cumulative distribution curves were created in Excel to compare the shift in curves from baseline and 1 month and 1 year after MMR3 receipt. The researchers 194 of 200 persons from the longitudinal study; 113 (58.2%) were enrolled, 45 (23.2%) refused, and 36 (18.5%) were ineligible (15 had previously received MMR3, and 21 had other reasons). To achieve adequate sample size, researchers contacted 1379 of 1795 additional persons (76.8%). Of those, 572 (41.4%) were enrolled, 664 (48.2%) refused, and 143 (10.4%) were ineligible (4 had previously received MMR3, and 139 had other reasons). Baseline serum samples were obtained from 685 enrolled subjects. 20 cohort 1 subjects (2.9%) were excluded who had medium or high concentrations of antibody for all 3 antigens throughout the longitudinal study and were, therefore, not given MMR3. An additional 3 (0.4%) were excluded because the only had baseline samples. There were 662 subjects (96.6%) who received MMR3 and provided a serum specimen at 1 month; 617 (92.6%) provided a specimen at 1 year. Subjects were aged 18-28 years (mean age plus or minus standard deviation 20.8 plus or minus 2.1 years); 294 (44.4%) were male. The mean interval between the second and third MMR doses was 15.8 years (range, 6.7-20.4 years). Of 662 subjects at baseline, 1 (0.2%) was seronegative, 23 (3.5%) had low MeV neutralizing antibody concentrations, 337 (50.9%) had medium concentrations and 301 (45.5%) had high concentrations. The seronegative subject was a female aged 20 years who received her last MMR dose 18 years prior. At 1 month and 1 year after MMR3 receipt, she had medium MeV neutralizing antibody concentrations. Of 23 subjects with low baseline antibody concentrations, 1 was seronegative, 5 had low concentrations, 14 had medium concentrations, and 3 had high concentrations 1 month after MMR3 receipt. One year after MMR3 receipt, 19 of 23 had serum specimens collected; 5 had low, 14 had medium and 0 had high MeV neutralizing antibody concentrations. Overall, at 1 month after MMR3 receipt, 1 of 662 subjects (0.2%) had no detectable MeV neutralizing antibodies, 6 (0.9%) had low MeV neutralizing antibody concentrations, 256 (38.7%) had medium neutralizing antibody concentrations, and 399 (60.3%) had high MeV neutralizing antibody concentrations. One year after MMR3 receipt, all 617 subjects who returned were positive for MeV neutralizing antibodies; 10 (1.6%) had low concentrations, 299 (48.5%) had medium concentrations, and 308 (49.9%) had high concentrations. The action taken with MMR II was unknown. The outcome of the event was unknown. The investigator considered the event to be related to MMR II. Additional information has been requested.