Table 2.
Maternal Hemagglutination Inhibition Antibody Responses
| Time Point | Subjects, No. | Seroprotectiona (%) (95% CI) | Geometric Mean Titer (95% CI) | Seroresponseb (%) (95% CI) | Complete Responsec (%) (95% CI) |
|---|---|---|---|---|---|
| Entry | 127 | 21 (15–29) | 14 (12–17)d | … | … |
| 21 d post–dose 1 | 119 | 73 (64–81)e | 85 (66–111)f | 66 (57–75) | 61 (51–69) |
| 10 d post–dose 2 | 107 | 80 (72–87)e,g | 92 (72–116)f | 72 (62–80) | 65 (56–74) |
| 21 d post–dose 2 | 94 | 77 (67–85)e | 81 (62–106)f,h | 67 (57–76) | 63 (52–73) |
| Delivery | 115 | 67 (58–75)e,g | 54 (43–69)f,h | 57 (48–67)i | 51 (42–61)j |
| 3 mo postdelivery | 105 | 60 (50–69)e | 39 (32–49)f,h | 51 (41–61) | 46 (36–56) |
| 6 mo postdelivery | 66 | 59 (46–71)e | 39 (30–51)f | 58 (45–70) | 48 (36–61) |
Abbreviation: CI, confidence interval; HAI, hemagglutination inhibition.
Entry antibody titers were analyzed for subjects who received at least the first vaccination. Antibody responses after the first vaccination were analyzed for subjects with available data who received the first vaccine dose and had the day 21 postvaccine dose 1 visit prior to delivery. Responses 10 and 21 days after the second vaccination were analyzed for women with available data who received both doses of vaccine and had the respective visits prior to delivery. Maternal antibody levels at delivery and 3 and 6 months postdelivery were analyzed for those women with available data who received both doses of vaccine and delivered subsequent to the 10-day postvaccine dose 2 timepoint.
a Seroprotection defined as HAI titer ≥40.
b Seroresponse defined as ≥4-fold rise in HAI titer from entry.
c Complete response defined as HAI titer ≥40 and ≥4-fold rise in HAI titer from entry.
d Baseline titers did not differ according to whether seasonal influenza vaccine had been received prior to entry (P = .7).
e P < .0001 (McNemar test) for the comparison to seroprotection at entry.
f P < .0001 (sign test) for the comparison to geometric mean titer at entry.
g P ≤ 008 (McNemar test) for the comparison to seroprotection at previous timepoint.
h P ≤ .04 (sign test) for the comparison to geometric mean titer at previous timepoint.
i P = .007 (McNemar test) for the comparison to seroresponse at previous timepoint.
j P = .007 (McNemar test) for the comparison to complete response at previous timepoint.