Table 2. Neonatal and Early Infant Outcomes.
| Pre-IPTW | Post-IPTWa | |||||
|---|---|---|---|---|---|---|
| Unvaccinated (n = 7591) | Vaccinated (n = 16 697) | Risk ratio (95% CI) | Unvaccinated (n = 7452) | Vaccinated (n = 16 738) | Risk ratio (95% CI) | |
| Follow-up time, d | 152 (88-209) | 126 (76-179) | 130 (71-197) | 134 (81-185) | ||
| Gestational age at delivery, No.(%) | ||||||
| <37 wk (Overall preterm) | 315 (4.1) | 730 (4.4) | 1.10 (0.95-1.27) | 358 (4.8) | 699 (4.2) | 0.95 (0.83-1.10) |
| <32 wk (Early preterm) | 48 (0.6) | 60 (0.4) | 0.52 (0.33-0.82) | 62 (0.8) | 60 (0.4) | 0.45 (0.29-0.70) |
| 32-36 wk (Late preterm) | 267 (3.5) | 670 (4.0) | 1.18 (1.02-1.38) | 296 (4.0) | 638 (3.8) | 1.03 (0.89-1.20) |
| Birth weight, No. (%) | ||||||
| SGA | 468 (6.7) | 1040 (6.6) | 0.98 (0.88-1.09) | 473 (6.9) | 1053 (6.7) | 0.97 (0.87-1.08) |
| Low birth weight, <2500 g | 324 (4.6) | 730 (4.6) | 0.98 (0.86-1.13) | 352 (5.1) | 705 (4.5) | 0.89 (0.78-1.01) |
| Very low birth weight, <1500 g | 43 (0.6) | 47 (0.3) | 0.44 (0.27-0.70) | 53 (0.8) | 49 (0.3) | 0.41 (0.26-0.65) |
| Unknown, No. | 619 | 833 | 561 | 932 | ||
| All-cause hospitalizations, No. (%) | ||||||
| Neonatal (1-28 d after birth) | 416 (5.5) | 916 (5.5) | 1.00 (0.89-1.13) | 408 (5.5) | 911 (5.4) | 0.99 (0.88-1.12) |
| Postneonatal (>28 d after birth) | 475 (6.3) | 777 (4.7) | 0.87 (0.78-0.98) | 398 (5.3) | 846 (5.1) | 0.95 (0.84-1.07) |
| Phototherapy | 71 (0.9) | 205 (1.2) | 1.31 (1.01-1.73) | 73 (1.0) | 203 (1.2) | 1.24 (0.95-1.63) |
| Infant death over the study period | 8 (0.1) | 22 (0.1) | 1.43 (0.66-3.43) | 13 (0.2) | 24 (0.1) | 0.84 (0.43-1.72) |
Abbreviations: IPTW, inverse probability of treatment weights; SGA, small for gestational age.
a
IPTW was used to balance groups in terms of maternal age, conception timing, parity, seasonal influenza vaccination, population subgroup, and socioeconomic status. Post-IPTW numbers slightly differ from crude pre-IPTW because of propensity weighting.