Table 3. Proportions of vaccinated participants reaching hemagglutination inhibition antibody titers of ≥1:40, ≥1:80, ≥1:160 on one-month post vaccination.
| IIV3 vaccine strain | HI titer cut point | Seroprotection on Day 28 among vaccinated participants* | p-value | |
|---|---|---|---|---|
| Pregnant (n = 33) % (95% CI) | Non-pregnant (n = 33) % (95% CI) | |||
| A/Michigan/45/2015 (H1N1)pdm09 | ≥1:40 | 88.2 (75.0, 101.4) | 78.7 (65.2, 92.2) | 0.517 |
| ≥1:80 | 73.5 (61.6, 85.4) | 65.9 (53.8, 78.0) | 0.263 | |
| ≥1:160 | 67.7 (55.4, 80.0) | 54.2 (41.7, 66.8) | 0.119 | |
| A/Singapore/INFIMH-16-0019/2016 (H3N2) | ≥1:40 | 91.7 (78.7, 104.7) | 92.6 (79.6, 105.7) | 0.896 |
| ≥1:80 | 84.9 (72.5, 97.2) | 77.6 (65.2, 90.0) | 0.565 | |
| ≥1:160 | 62.7 (50.2, 75.2) | 67.1 (54.6, 79.6) | 0.921 | |
| B/Phuket/3073/2013 | ≥1:40 | 88.1 (77.6, 98.6) | 82.0 (71.4, 92.7) | 0.434 |
| ≥1:80 | 78.7 (67.1, 90.4) | 65.1 (53.3, 76.8) | 0.256 | |
| ≥1:160 | 38.6 (26.7, 50.5) | 50.4 (38.4, 62.4) | 0.466 | |
Abbreviations: IIV3, trivalent inactivated influenza vaccine; HI, hemagglutination inhibition; CI, confidence interval.
*Point estimates, 95% CI, and p-values calculated using multilevel regression, controlling for previous year vaccination and baseline antibody titer.