Table 3.
Unadjusted and Adjusted Vaccine Effectiveness Stratified by Combinations of Prior (2013–2014) and Current (2014–2015) Influenza Vaccination Status Among Patients Aged ≥9 Years
| Vaccination Status | Influenza-Positive Cases |
Influenza-Negative Controls |
Unadjusted | Adjusteda | ||
|---|---|---|---|---|---|---|
| No. Cases/ Row Total | (%) | No. Controls/ Row Total | (%) | VE, % (95% CI) | VE, % (95% CI) | |
| Influenza A/H3N2b | ||||||
| Vaccinated current 2014–2015 only | 175/910 | (19.2) | 735/910 | (80.8) | 15 (−4 to 30) | 8 (−14 to 26) |
| Vaccinated current 2014–2015 and prior 2013–2014 | 576/2564 | (22.5) | 1988/2564 | (77.5) | −4 (−19 to 9) | −2 (−20 to 13) |
| Vaccinated prior 2013–2014 only | 133/589 | (22.6) | 456/589 | (77.4) | −5 (−30 to 16) | 3 (−23 to 23) |
| Not vaccinated either 2013–2014 or 2014–2015 | 461/2115 | (21.8) | 1654/2115 | (78.2) | REF | REF |
| Influenza B/Yamagatac | ||||||
| Vaccinated current 2014–2015 only | 23/758 | (3.0) | 735/758 | (97.0) | 61 (39 to 75) | 59 (34 to 74) |
| Vaccinated current 2014–2015 and prior 2013–2014 | 85/2073 | (4.1) | 1988/2073 | (95.9) | 47 (30 to 60) | 56 (39 to 68) |
| Vaccinated prior 2013–2014 only | 21/477 | (4.4) | 456/477 | (95.6) | 43 (8 to 34) | 43 (7 to 65) |
| Not vaccinated either 2013–2014 or 2014–2015 | 133/1787 | (7.4) | 1654/1787 | (92.6) | REF | REF |
Abbreviations: CI, confidence interval; REF, reference; VE, vaccine effectiveness.
a Adjusted for site, age (spline), any high-risk International Classification of Diseases, 9th Edition, Clinical Modification code in the year prior to enrollment, and calendar time.
b The P value for interaction of prior (2013–2014) and current (2014–2015) season vaccination was .40.
c The P value for interaction of prior (2013–2014) and current (2014–2015) season vaccination was .07.