Table 2.
Reenrolled Participants Developing Influenza and Relative Vaccine Efficacy
| Vaccination Patterna |
Laboratory-Confirmed Influenzab, Any Strain |
Culture-Confirmed Influenzab, Any Strain |
Laboratory-Confirmed Influenzab, Vaccine-Similar Strains |
Culture-Confirmed Influenzab, Vaccine-Similar Strains |
||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Y1 | Y2 | No. | Cases, No. (%) | Relative VE, %c (95% CI) | Cases, No. (%) | Relative VE, %c (95% CI) | Cases, No. (%) | Relative VE, %c (95% CI) | Cases, No. (%) | Relative VE, %c (95% CI) |
| IIV-HD | IIV-HD | 1943 | 52 (2.7) | 25.1 (−8.9 to 48.8) | 47 (2.4) | 28.2 (−6.2 to 51.7) | 17 (0.9) | 23.2 (−51.4 to 61.7) | 16 (0.8) | 27.8 (−44.0 to 64.5) |
| IIV-SD | IIV-HD | 1880 | 46 (2.4) | 31.6 (−.8 to 53.9) | 43 (2.3) | 32.1 (−1.4 to 54.9) | 17 (0.9) | 20.7 (−56.4 to 60.5) | 16 (0.9) | 25.3 (−48.8 to 63.3) |
| IIV-HD or -SD | IIV-HD | 3823 | 98 (2.6) | 28.3 (1.0–47.8) | 90 (2.4) | 30.1 (2.3–49.8) | 34 (0.9) | 22.0 (−40.0 to 55.7) | 32 (0.8) | 26.6 (−32.6 to 58.6) |
| IIV-HD | IIV-SD | 1890 | 60 (3.2) | 11.2 (−27.4 to 38.2) | 55 (2.9) | 13.6 (−25.7 to 40.8) | 27 (1.4) | −25.3 (−131 to 31.3) | 26 (1.4) | −20.7 (−123 to 34.2) |
| IIV-SD | IIV-SD | 1930 | 69 (3.6) | Reference | 65 (3.4) | Reference | 22 (1.1) | Reference | 22 (1.1) | Reference |
Abbreviations: CI, confidence interval; IIV-HD, high-dose inactivated influenza vaccine; IIV-SD, standard-dose inactivated influenza vaccine; VE, vaccine efficacy; Y1, year 1; Y2, year 2.
a Based on vaccine assigned on randomization in Y2, and vaccine actually received in Y1.
b Confirmed influenza associated with protocol-defined influenza-like illness in Y2.
c Efficacy relative to Y1 IIV-SD, Y2 IIV-SD vaccination pattern. Confidence intervals for relative VE were calculated by the Clopper–Pearson exact method conditional on the total number of cases.