Table 1.
Characteristics of the Sample, by Vaccination Group
| Variable | Total (N = 2000) | Immunized at ≤15 mo (n = 360) | Immunized at 16–23 mo (n = 958) | Immunized at ≥24 mo (n = 682) | P Value | |||
|---|---|---|---|---|---|---|---|---|
| Overall |
≤15 vs 16–23 mo | ≤15 vs ≥24 mo | 16–23 vs ≥24 mo | |||||
| Age at enrollment, y, mean ± SD (range) | 21.1 ± 2.4 (18.0–38.0) | 20.7 ± 2.0 (18.0–28.0) | 20.8 ± 2.2 (18.0–35.0) | 21.8 ± 2.8 (18.0–38.0) | < .0001 | .749 | < .0001 | < .0001 |
| Female sex, No. (%) | 1387 (69.4) | 239 (66.4) | 680 (71.0) | 468 (68.6) | .240 | .463 | .106 | .304 |
| Protective IgG titer at enrollment, No. (% [95% CI]) | 1695 (84.8 [83.1–86.3]) | 288 (80.0 [75.5–84.0]) | 794 (82.9 [80.3–85.2]) | 613 (89.9 [87.4–92.0]) | < .0001 | < .0001 | < .0001 | .224 |
| GMT IgG value at enrollment, AU/mL (95% CI) | 77.2 (73.0–81.6) | 58.5 (51.2–66.9) | 71.7 (65.6–77.9) | 99.1 (90.7–108.2) | < .0001 | .007 | < .0001 | < .0001 |
| Seroconverted after third MMR booster dose, No. (% [95% CI]) | 157/212 (74.1 [67.6–79.8]) | 40/52 (76.9 [62.8–80.2]) | 80/111 (72.1 [66.0–80.1]) | 37/49 (75.5 [61.1–86.7]) | .777 | .512 | .868 | .651 |
| IgG value after third MMR booster dose in seronegative subjects at enrollment, GMT, AU/mL (95% CI) | 46.1 (39.1–54.4) | 51.1 (36.5–71.5) | 43.7 (34.4–55.7) | 46.7 (34.1–64.0) | .762 | .693 | 1.000 | 1.000 |
Abbreviations: CI, confidence interval; GMT, geometric mean titer; IgG, immunoglobulin G; MMR, measles-mumps-rubella vaccine; SD, standard deviation.