Table 3.
Association of influenza vaccination during pregnancy with the risk of preterm delivery (PTD) among mothers of non-malformed infants, stratified by influenza season
| All | PTD | Unadjusted | Adjusteda | |||||
|---|---|---|---|---|---|---|---|---|
| Influenza vaccination timing | n | % | n | % | HR | [95% CI] | HR | [95% CI] |
| 2006–07 Season | ||||||||
| All | 436 | 100.0 | 33 | 7.6 | ||||
| None | 365 | 83.7 | 29 | 7.9 | ||||
| Anytime during pregnancy | 71 | 16.3 | 4 | 5.6 | 0.79 | [0.28, 2.26] | 1.03 | [0.32, 3.33] |
| 2007–08 Season | ||||||||
| All | 585 | 100.0 | 43 | 7.4 | ||||
| None | 482 | 82.4 | 38 | 7.9 | ||||
| Anytime during pregnancy | 103 | 17.6 | 5 | 4.9 | 0.64 | [0.25, 1.63] | 0.79 | [0.28, 2.21] |
| 2008–09 Season | ||||||||
| All | 529 | 100.0 | 29 | 5.5 | ||||
| None | 425 | 80.3 | 23 | 5.4 | ||||
| Anytime during pregnancy | 104 | 19.7 | 6 | 5.8 | 1.12 | [0.46, 2.75] | 1.08 | [0.40, 2.95] |
| 2009–10 Seasonb | ||||||||
| All | 378 | 100.0 | 21 | 5.6 | ||||
| None | 346 | 91.5 | 12 | 3.5 | ||||
| Anytime during pregnancy | 32 | 8.5 | 9 | 28.1 | 9.96 | [4.19, 23.7] | 7.81 | [2.66, 23.0] |
a
Adjusted for propensity score.
b
Represents the unvaccinated and the vaccinated against seasonal influenza only; 385 vaccinated against pandemic H1N1 were excluded from the analysis (including 20 PTD).
PTD, preterm delivery; HR, hazard ratio; CI, confidence interval.