Table 2.
Overall and Strain-Specific, Vaccine Effectiveness Against Hospitalization With Laboratory-Confirmed Influenza, Hospitalized Adult Influenza Vaccine Effectiveness Network 2016–2018 (N = 6129)
| Outcome | Year | Vaccinateda Positives, n/Total (%) | Unvaccinated Positives, n/Total (%) | Unadjusted VE (95% CI) | Adjustedb VE (95% CI) |
|---|---|---|---|---|---|
| Influenza, all | 2016–2017 | 302/1886 (16.0) | 161/719 (22.4) | 33.4 (17.5 to 46.3) | 30.6 (12.4 to 45.0) |
| 2017–2018 | 557/2350 (23.7) | 353/1174 (30.1) | 26.6 (14.2 to 37.3) | 34.2 (21.9 to 44.6) | |
| 2016–2018 (2 y) | 859/4236 (20.3) | 514/1893 (27.2) | 31.0 (21.7 to 39.2) | 33.5 (23.6 to 42.0) | |
| A/H3N2 | 2016–2017 | 214/1658 (12.9) | 95/596 (15.9) | 21.4 (−2.2 to 39.5) | 18.0 (−9.2 to 38.3) |
| 2017–2018 | 343/2044 (16.8) | 187/970 (19.3) | 14.9 (−3.7 to 30.1) | 23.8 (5.3 to 38.7) | |
| 2016–2018 (2 y) | 557/3702 (15.0) | 282/1566 (18.0) | 18.8 (5.0 to 30.6) | 22.8 (8.3 to 35.0) | |
| A/H1N1 pdm09 | 2016–2017 | 7/391 (1.8) | 4/150 (2.7) | … | … |
| 2017–2018 | 48/1567 (3.1) | 56/729 (7.7) | 61.92 (43.4 to 74.4) | 56.1 (33.1 to 71.2)c | |
| 2016–2018 (2 y) | 55/1958 (2.8) | 60/879 (6.8) | 60.5 (42.5 to 72.8) | 53.7 (31.4 to 68.7)c | |
| B/Yamagata | 2016–2017 | 56/1356 (4.1) | 39/502 (7.8) | 45.0 (15.1 to 64.3) | 47.9 (16.8 to 67.3) |
| 2017–2018 | 119/1615 (7.4) | 82/738 (11.1) | 36.2 (14.1 to 52.5) | 50.2 (31.4 to 63.8) | |
| 2016–2018 (2 y) | 175/2971 (5.9) | 121/1240 (9.8) | 42.0 (26.1 to 54.4) | 49.4 (34.3 to 61.1) |
Abbreviations: CI, confidence interval; VE, vaccine effectiveness.
aAll denominators exclude other influenza types and any enrollments occurring outside of influenza type-specific periods for each site.
bAdjusted VE models are adjusted for enrollment hospital, age (18–49, 50–64, 65–74, ≥75 y), race, tertiles (for 1 y) or 6 quantiles (for 2 y) of calendar time including a site-specific and influenza-type specific peak for each year, days from illness onset to specimen collection (0–1, 2–4, 5–10 d), self-reported health (poor/fair vs good/very good/excellent), and self-reported past year hospitalizations.
cVE could not be calculated due to small numbers in 2016–2017. Adjusted VE models for A/H1N1 are adjusted for site instead of enrollment hospital due to small case numbers per hospital.