Table 2.
Analysis of Birth Outcomes by Maternal Vaccination Status and Influenza Activity Among Women Who Had Live Births (n = 4854)
| Outcome | Total N (%) | Vaccinated N (%) | Unvaccinated N (%) |
P Value for Crude Analysis |
Crude Risk to Vaccinated (95% CI) |
Adjusteda Risk Ratio to Vaccinated (95% CI) |
|---|---|---|---|---|---|---|
| Proportion small for gestational age | 156/3699 (4.2) | 85/1811 (4.7) | 71/1888 (3.8) | .16 | 1.25 (.92–1.70) | 1.25 (.91–1.72) |
| High influenza activity | 129/3129 (4.1) | 71/1532 (4.6) | 58/1597 (3.6) | .16 | 1.28 (.91–1.79) | 1.22 (.86–1.74) |
| Low influenza activity | 27/570 (4.7) | 14/279 (5.0) | 13/291 (4.5) | .76 | 1.12 (.54–2.35) | 1.50 (.71–3.17) |
| Proportion preterm | 378/3709 (10.2) | 136b/1819 (7.5) | 242/1890 (12.8) | <.001 | 0.58 (.48–.71) | 0.70 (.57–.87) |
| High influenza activity | 316/3137 (10.1) | 111/1538 (7.2) | 205/1599 (12.8) | <.001 | 0.56 (.45–.70) | 0.69 (.55–.87) |
| Low influenza activity | 62/572 (10.8) | 25/281 (8.9) | 37/291 (12.7) | .14 | 0.70 (.43–1.13) | 0.83 (.50–1.37) |
| Difference in means (vaccinated–unvaccinated) |
Difference in marginal means (vaccinated–unvaccinated) |
|||||
| Mean birth weight, g (standard deviation) | 3070 g (451) | 3082 g (423) | 3060 g (471) | .09 | +22 g | +1.6 gc |
| High influenza activity (n = 4079) | 3077 g (453) | 3092 g (425) | 3065 g (473) | .06 | +27 g | +9 gd |
| Low influenza activity (n = 767) | 3035 g (439) | 3030 g (412) | 3039 g (458) | .78 | −9 g | −39 ge |
Abbreviations: CI, confidence interval; g, grams.
Adjusted for mother’s age, parity, province, ethnicity, education, income, number of antenatal visits, number of household members, and distance to hospital. The model for the first row for each outcome includes births occurring at any point (April 2014– February 2015) with a term included for influenza activity (high/low). The model for the row “high influenza activity” only includes births occurring in months August 2014–February 2015 and the model for the row “low influenza period” only includes births occurring in the months April–July 2014. For these models, the term for influenza activity was not included in the model.
The proportion of infants born preterm by trimester of maternal vaccination: 42/441 (9.5%) first trimester, 83/976 (8.5%) second trimester, 11/402 (2.7%) third trimester (P < .001).
Mean and 95% Wald CI for vaccinated (3019 g, 2987–3051) and unvaccinated (3018 g, 2990–3051).
Mean and 95% Wald CI for vaccinated (3043 g, 3010–3076) and unvaccinated (3034 g, 3006–3062).
Mean and 95% Wald CI for vaccinated (2957 g, 2888–3027) and unvaccinated (2996 g, 2940–3051).