Table 2.
Sensitivity Analyses for Estimated Effectiveness of Maternal Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Influenza Among Infants <6 Months of Age
| Sensitivity Analysis | Influenza-Positive Cases | Influenza-Negative Controls | Adjusted OR (95% CI)a | Vaccine Effectiveness, % (95% CI)a,b |
|---|---|---|---|---|
| Primary outcome | ||||
| Reclassify those who received previous season's vaccine as vaccinated | 56/1783 (3.1) | 1897/22 077 (8.6) | 0.41 (.31–.54) | 59 (46–69) |
| Reclassify those vaccinated within 14 d of birth as vaccinated | 56/1783 (3.1) | 1867/22 077 (8.5) | 0.41 (.31–.54) | 59 (46–69) |
| Reclassify those who received previous season's vaccine and those vaccinated within 14 d of birth as vaccinated | 70/1783 (3.9) | 2098/22 077 (9.5) | 0.44 (.35–.57) | 56 (43–65) |
| Add gestational age at birth, wk, to fully adjusted model | 42/1783 (2.4) | 1666/22 077 (7.5) | 0.36 (.26–.49) | 64 (51–74) |
| Add rural/urban status to fully adjusted model | 42/1783 (2.4) | 1666/22 077 (7.5) | 0.35 (.26–.48) | 65 (52–74) |
| Add any maternal preexisting medical comorbidity to fully adjusted model | 42/1783 (2.4) | 1666/22 077 (7.5) | 0.35 (.26–.49) | 65 (51–74) |
| Limit to health care encounters with an ARI code, hospitalizations and ED visitsc | 30/1381 (2.2) | 793/9852 (8.0) | 0.29 (.20–.42) | 71 (58–80) |
| Secondary outcome | ||||
| Limit control group to hospitalized infants who tested negative for influenzad | 24/933 (2.6) | 1051/12 877 (8.2) | 0.34 (.22–.51) | 66 (49–78) |
Data are number of infants born to vaccinated mothers/total number of infants (%).
Abbreviations: ARI, acute respiratory infection; CI, confidence interval; ED, emergency department; ICD-10, CM International Classification of Diseases-Tenth Revision; OR, odds ratio.
aAdjusted for infant age at test, season of birth, prenatal care adequacy, neighborhood income, and influenza season.
bVaccine effectiveness was estimated as 1 minus the adjusted OR, comparing the odds of maternal influenza vaccination during pregnancy among test-positive infant cases relative to test-negative infant controls.
cARI codes: ICD-10 codes B34, B97, J00-J06, J09-J18, J20-J22, J39.8, J39.9, J40, J45, J80, J81, J96, J98, R05, R06.0-R6.2, R06.4, R06.7, R06.8, R07.0, R07.1, R09.2, R09.3, R50, R53.
dCase and control specimens were limited to those collected during an admission to a hospital ward or intensive care unit.