Table 2.
Inactivated Influenza Vaccine Effectiveness Against Hospitalization Among Children Aged 6 Months to 17 Years, 2012–2013 to 2016–2017
| Estimated Vaccine Effectiveness, a % (95% Confidence Interval)) | ||||
|---|---|---|---|---|
| Inactivated Influenza Vaccine Effectiveness by Characteristic | Cases Who Were Vaccinated, No./Total No. (%) | Controls Who Were Vaccinated, No./Total No. (%) | Unadjusted | Adjustedb |
| Overall | 132/490 (26.9) | 209/490 (42.7) | 50.4 (35.2 to 62.1) | 51.3 (34.8 to 63.6) |
| Influenza B–infected casesc | 43/139 (30.9) | 209/490 (42.7) | 39.8 (10.0 to 59.7) | 37.1 (2.3 to 59.5) |
| Influenza A–infected casesc | 89/352 (25.3) | 209/490 (42.7) | 54.5 (38.6 to 66.3) | 54.7 (37.4 to 67.3) |
| By age group, y | ||||
| 0 to <5 | 49/214 (22.9) | 98/214 (45.8) | 64.8 (46.7 to 76.8) | 64.3 (44.1 to 77.1) |
| 5 to <9 | 42/127 (33.1) | 47/122 (38.5) | 21.2 (–32.5 to 53.1) | 17.1 (–44.6 to 52.5) |
| 9+ | 41/149 (27.5) | 64/154 (41.6) | 46.6 (13.6 to 67.0) | 52.2 (19.5 to 71.6) |
| By season | ||||
| 2012–2013 | 39/128 (30.5) | 43/128 (33.6) | 13.4 (–46.5 to 48.8) | 12.0 (–54.4 to 49.9) |
| 2013–2014 | 7/56 (12.5) | 26/56 (46.4) | 83.5 (57.4 to 93.6) | 83.6 (55.3 to 94.0) |
| 2014–2015 | 29/116 (25.0) | 52/116 (44.8) | 59.0 (28.4 to 76.5) | 62.3 (31.9 to 79.1) |
| 2015–2016 | 18/70 (25.7) | 41/70 (58.6) | 75.5 (49.9 to 88.0) | 74.4 (45.4 to 88.0) |
| 2016–2017 | 39/120 (32.5) | 47/120 (39.2) | 25.2 (–27.0 to 56.0) | 24.4 (–33.6 to 57.1) |
| Immunocompromised | ||||
| Yes | 31/67 (46.3) | 43/63 (68.3) | 59.9 (18.1 to 80.4) | 43.5 (–23.3 to 74.1) |
| No | 101/423 (23.9) | 166/427 (38.9) | 50.7 (33.7 to 63.3) | 52.4 (34.9 to 65.2) |
| Cases and controls admitted to the intensive care unit | 26/134 (19.4) | 65/192 (33.9) | 53.0 (20.7 to 72.1) | 51.3 (14.7 to 72.1) |
| Cases and controls with radiographic pneumoniad | 22/114 (19.3) | 39/97 (40.2) | 64.4 (34.1 to 80.8) | 65.5 (32.3 to 82.4) |
| Time of the season | ||||
| Early | 61/245 (24.9) | 109/252 (43.3) | 56.5 (36.3 to 70.3) | 58.1 (36.8 to 72.2) |
| Late | 71/245 (29.0) | 100/238 (42.0) | 43.7 (17.9 to 61.4) | 43.4 (15.1 to 62.3) |
| Cases and controls hospitalized during peak influenza circulatione | 130/465 (28.0) | 194/446 (43.5) | 49.6 (33.6 to 61.7) | 50.6 (33.4 to 63.4) |
aCalculated as (1 – odds ratio [OR]) × 100%, where OR is the odds of vaccination among cases compared with the odds of vaccination among controls.
bAdjusted for demographic characteristics (age at admission in years, sex, race/ethnicity, study hospital, and season), neurologic disorder, and chronic conditions with significant bivariate associations with vaccination or case status as identified in Table 1 (blood disorder, cardiac disorder, immunocompromised status, kidney disorder, hematologic malignancy, solid organ malignancy, and respiratory disorder).
cOne case coinfected with influenza A and B included in both subgroups.
dDefined by International Classification of Diseases, Ninth Revision, Clinical Modification, codes before October 2015 and International Classification of Diseases, Tenth Revision, Clinical Modification, codes beginning in October 2015.
ePeriod within each season when >4% of all sampling was positive.