Odds of seasonal influenza vaccination by maternal and child characteristics for children born in Western Australia between 1 April 2012 and 1 July 2016
| Characteristic | Maternally unvaccinated (n=124 851) n (%) | Maternally vaccinated (n=15 663) n (%) | OR (95% CI) |
| Maternal characteristics | |||
| Age (years) | 1.01 (1.00 to 1.01) | ||
| ≤19 | 3942 (3.2) | 501 (3.2) | 1.12 (1.01 to 1.25) |
| 20–24 | 17 188 (13.8) | 1947 (12.4) | Reference |
| 25–29 | 35 774 (28.7) | 4329 (27.6) | 1.07 (1.01 to 1.13) |
| 30–34 | 42 177 (33.8) | 5573 (35.6) | 1.17 (1.10 to 1.23) |
| ≥35 | 25 770 (20.6) | 3313 (21.2) | 1.13 (1.07 to 1.20) |
| Aboriginal status | |||
| Aboriginal | 6503 (5.2) | 832 (5.3) | 1.02 (0.95 to 1.10) |
| Non-Aboriginal | 118 348 (94.8) | 14 831 (94.7) | Reference |
| Socioeconomic status* | |||
| Quintile 1 (most disadvantaged) | 24 965 (20.0) | 2925 (18.7) | 0.89 (0.85 to 0.94) |
| Quintile 2 | 25 681 (20.6) | 3277 (20.9) | 0.97 (0.92 to 1.03) |
| Quintile 3 | 26 558 (21.3) | 3248 (20.7) | 0.93 (0.89 to 0.98) |
| Quintile 4 | 24 787 (19.9) | 3219 (20.6) | 0.99 (0.94 to 1.05) |
| Quintile 5 (least disadvantaged) | 22 860 (18.3) | 2994 (19.1) | Reference |
| Body mass index | 1.00 (1.00 to 1.00) | ||
| <18.5 (underweight) | 4243 (3.4) | 501 (3.2) | 0.92 (0.84 to 1.01) |
| 18.5 to <25 (normal) | 59 174 (47.4) | 7582 (48.4) | Reference |
| 25 to <30 (overweight) | 35 544 (28.5) | 4302 (27.5) | 0.94 (0.91 to 0.98) |
| ≥30 (obese) | 25 890 (20.7) | 3278 (20.9) | 0.99 (0.95 to 1.03) |
| Parity | |||
| Primiparous | 53 244 (42.7) | 7335 (46.8) | Reference |
| 1 prior birth | 43 296 (34.7) | 5405 (34.5) | 0.91 (0.87 to 0.94) |
| ≥2 prior births | 28 311 (22.7) | 2923 (18.7) | 0.75 (0.72 to 0.78) |
| Pre-existing medical conditions | |||
| Asthma† | 12 859 (10.3) | 1731 (11.1) | 1.08 (1.03 to 1.14) |
| Essential hypertension† | 1623 (1.3) | 282 (1.8) | 1.39 (1.23 to 1.58) |
| Pre-existing diabetes mellitus† | 1044 (0.8) | 202 (1.3) | 1.55 (1.33 to 1.80) |
| Pregnancy complications | |||
| Gestational diabetes† | 12 487 (10.0) | 969 (6.2) | 0.59 (0.55 to 0.63) |
| Gestational hypertension† | 5719 (4.6) | 464 (3.0) | 0.64 (0.58 to 0.70) |
| Pre-eclampsia† | 4107 (3.3) | 319 (2.0) | 0.61 (0.54 to 0.69) |
| Smoked during pregnancy | 12 549 (10.1) | 1403 (9.0) | 0.88 (0.83 to 0.93) |
| Trimester at the first prenatal care visit | |||
| First trimester | 82 329 (65.9) | 11 131 (71.1) | Reference |
| Second trimester | 36 161 (29.0) | 4075 (26.0) | 0.83 (0.80 to 0.87) |
| Third trimester | 6130 (4.9) | 449 (2.9) | 0.54 (0.49 to 0.60) |
| No prenatal care | 231 (0.2) | 8 (0.1) | 0.26 (0.13 to 0.52) |
| Year of birth | |||
| 2012 | 22 844 (18.3) | 1400 (8.9) | Reference |
| 2013 | 29 458 (23.6) | 3165 (20.2) | 1.75 (1.64 to 1.87) |
| 2014 | 29 827 (23.9) | 3513 (22.4) | 1.92 (1.80 to 2.05) |
| 2015 | 27 444 (22.0) | 5558 (35.5) | 3.30 (3.11 to 3.51) |
| 2016 | 15 278 (12.2) | 2027 (12.9) | 2.16 (2.02 to 2.32) |
| Season of birth | |||
| Summer (December–February) | 30 700 (24.6) | 2382 (15.2) | Reference |
| Autumn (March–May) | 36 337 (29.1) | 2524 (16.1) | 0.90 (0.84 to 0.95) |
| Winter (June–August) | 29 431 (23.6) | 5893 (37.6) | 2.58 (2.45 to 2.71) |
| Spring (September–November) | 28 383 (22.7) | 4864 (31.1) | 2.21 (2.10 to 2.33) |
| Child characteristics | |||
| Sex‡ | |||
| Male | 64 244 (51.5) | 8005 (51.1) | Reference |
| Female | 60 604 (48.5) | 7658 (48.9) | 1.01 (0.98 to 1.05) |
| Aboriginal status | |||
| Aboriginal | 7043 (5.6) | 915 (5.8) | 1.04 (0.97 to 1.11) |
| Non-Aboriginal | 117 808 (94.4) | 14 748 (94.2) | Reference |
| Birth outcomes | |||
| Preterm birth | 8576 (6.9) | 980 (6.3) | 0.90 (0.85 to 0.97) |
| Moderate-to-late preterm | 7572 (6.1) | 908 (5.8) | 0.95 (0.88 to 1.02) |
| Very preterm | 644 (0.5) | 54 (0.3) | 0.66 (0.50 to 0.88) |
| Extremely preterm | 360 (0.3) | 18 (0.1) | 0.40 (0.25 to 0.64) |
| Small-for-gestational age§ | 10 202 (8.2) | 1304 (8.3) | 1.02 (0.96 to 1.08) |
Bold values indicate statistically significant associations.
*Socioeconomic status was based on the Socioeconomic Index for Areas Index of Relative Socioeconomic Advantage and Disadvantage, an area-based index of relative access to resources for households within the same census collection district.15
†Comparisons were between the presence and absence of the condition by treatment groups.
‡The sex of <5 maternally unvaccinated children was unknown.
§Small-for-gestational age was based on the Australian national birth weight percentiles by sex and gestational age.31