Table 3.
Estimates of 18-Month Postintervention HAI and NAI Titers and Times to Decrease Titer by 2-fold, Stratified by Peak Postintervention Titera
| All Subjects N (%) | Model Estimated 18-Month Titer (95% CI)b | Days to 2-fold Titer Decrease (95% CI)b,c | |
|---|---|---|---|
| Influenza A (H3N2) | |||
| Peak HAI Titera | |||
| 4 | 15 (1.6) | 5 (4 to 6) | ∞ |
| 8 | 55 (5.8) | 9 (7 to 10) | ∞ |
| 16 | 86 (9.1) | 14 (13 to 16) | 173 623 (3188 to ∞) |
| 32 | 128 (13.6) | 24 (22 to 26) | 2945 (1672 to 12 345) |
| 64 | 147 (15.6) | 40 (37 to 43) | 1485 (1104 to 2269) |
| 128 | 153 (16.3) | 67 (62 to 72) | 993 (803 to 1300) |
| 256 | 110 (11.7) | 112 (103 to 122) | 746 (620 to 936) |
| 512 | 120 (12.8) | 187 (169 to 207) | 597 (499 to 742) |
| 1024 | 67 (7.1) | 312 (275 to 354) | 498 (416 to 619) |
| 2048 | 36 (3.8) | 521 (448 to 607) | 427 (356 to 533) |
| 4096 | 24 (2.6) | 871 (728 to 1042) | 374 (310 to 469) |
| Peak NAI Titera | |||
| 5 | 63 (11.8) | 5 (4 to 6) | ∞ |
| 10 | 61 (11.4) | 8 (7 to 8) | ∞ |
| 20 | 104 (19.4) | 12 (11 to 13) | 2508 (1557 to 6445) |
| 40 | 101 (18.8) | 18 (16 to 19) | 1135 (886 to 1578) |
| 80 | 61 (11.4) | 27 (25 to 29) | 734 (603 to 935) |
| 160 | 80 (14.9) | 41 (37 to 46) | 542 (452 to 677) |
| 320 | 35 (6.5) | 63 (55 to 72) | 430 (359 to 534) |
| 640 | 19 (3.5) | 96 (82 to 114) | 356 (297 to 443) |
| 1280 | 12 (2.2) | 147 (121 to 180) | 304 (254 to 379) |
| Influenza B Yamagata | |||
| Peak HAI Titera | |||
| 4 | 15 (1.6) | 6 (5 to 8) | ∞ |
| 8 | 20 (2.1) | 10 (9 to 12) | ∞ |
| 16 | 31 (3.3) | 17 (15 to 20) | ∞ |
| 32 | 92 (9.8) | 29 (26 to 33) | 96 097 (3253 to ∞) |
| 64 | 121 (12.9) | 49 (45 to 53) | 2455 (1523 to 6337) |
| 128 | 158 (16.8) | 81 (76 to 88) | 1244 (971 to 1728) |
| 256 | 159 (16.9) | 136 (126 to 146) | 833 (698 to 1032) |
| 512 | 135 (14.3) | 227 (209 to 247) | 626 (536 to 751) |
| 1024 | 104 (11.1) | 379 (343 to 420) | 501 (432 to 598) |
| 2048 | 53 (5.6) | 634 (558 to 719) | 418 (360 to 499) |
| 4096 | 53 (5.6) | 1058 (908 to 1234) | 359 (308 to 429) |
Abbreviations: CI, confidence interval; HAI, hemagglutination inhibition; NAI, neuraminidase inhibition.
a Titer at 1-month postvaccination follow-up.
b Rates of antibody change were estimated in linear mixed models with log2 titers as the dependent variable, time in days from the 1 month postvaccination blood draw as the independent variable, and an interaction term between the peak log2 titer and time. Because peak log2 titer was included in the model as a covariate, a separate intercept was not estimated and only post-1-month log2 titers were included in the dependent variable. To account for correlation of titers within individuals over time, time was modeled as a random effect.
c Time in days to decrease 2-fold (1 log2 titer) was calculated as the reciprocal of the model estimated rates.