Table 2.
Estimated absolute and relative efficacies of the trivalent inactivated influenza vaccine (TIV) and the live attenuated influenza vaccine (LAIV) during the 2005–2006 influenza season in Michigan.
| Relative reductiona (95% CI) |
|||||||||
|---|---|---|---|---|---|---|---|---|---|
| Cumulative incidence, no. (%) of participants |
RR (95% CI) |
Absolute efficacy |
|||||||
| End point | TIV (n = 867) |
LAIV (n = 853) |
Placebo (n = 338) |
TIV vs. placebo | LAIV vs. placebo | TIV vs. LAIV | TIV vs. placebo | LAIV vs. placebo | Relative efficacy, TIV vs. LAIV |
| Virus isolationb | 12 (1.4) | 6 (0.7) | 6 (1.8) | 0.77 (0.27 to 2.53) | 0.39 (0.11 to 1.48) | 1.95 (0.68 to 6.39) | 23 (−153 to 73) | 61 (−48 to 89) | −95 (−539 to 32) |
| Real-time PCR identification c | 12 (1.4) | 14 (1.6) | 6 (1.8) | 0.77 (0.27 to 2.53) | 0.92 (0.33 to 2.94) | 0.84 (0.36 to 1.96) | 23 (−153 to 73) | 8 (−194 to 67) | 16 (−96 to 64) |
| Virus isolation and/or real-time PCR identificationd | 13 (1.5) | 14 (1.6) | 6 (1.8) | 0.84 (0.30 to 2.71) | 0.92 (0.33 to 2.94) | 0.91 (0.40 to 2.10) | 16 (−171 to 70) | 8 (−194 to 67) | 9 (−110 to 60) |
| Seropositivitye | 10 (1.2) | 23 (2.7) | 14 (4.1) | 0.28 (0.11 to 0.67) | 0.65 (0.32 to 1.37) | 0.43 (0.18 to 0.93) | 72 (33 to 89) | 35 (−37 to 68) | 57 (7 to 82) |
| Virus isolation and/or seropositivityf | 19 (2.2) | 23 (2.7) | 16 (4.7) | 0.46 (0.23 to 0.96) | 0.57 (0.29 to 1.15) | 0.81 (0.42 to 1.56) | 54 (4 to 77) | 43 (−15 to 71) | 19 (−56 to 58) |
| Virus isolation and/or real-time PCR identification and/or seropositivityg | 19 (2.2) | 24 (2.8) | 16 (4.7) | 0.46 (0.23 to 0.96) | 0.60 (0.30 to 1.20) | 0.78 (0.40 to 1.48) | 54 (4 to 77) | 40 (−20 to 70) | 22 (−48 to 60) |
NOTE. The population was all 2058 enrolled participants who were randomly assigned to a vaccine or placebo group and who received vaccine or placebo. The TIV used was Fluzone (Sanofi Pasteur), and the LAIV used was FluMist (MedImmune). The placebo was physiologic saline administered as an intramuscular injection or normal allantoic fluid administered as an intranasal spray. Efficacy estimates were adjusted for participation in year 1 (2004–2005); exact 95% confidence intervals (CIs) were calculated. RR, relative risk; PCR, polymerase chain reaction.
Point estimates of vaccine efficacy were calculated as follows: (1−RR) × 100.
Defined as a symptomatic influenza illness episode that was laboratory-confirmed as influenza by isolation of virus in cell culture and identification by fluorescent antibody assay.
Defined as a symptomatic influenza illness episode that was laboratory-confirmed as influenza by means of real-time PCR assay.
A combined end point, defined as a symptomatic influenza illness episode that was laboratory-confirmed as influenza by virus isolation in cell culture and/or by means of real-time PCR assay.
Defined as a symptomatic influenza illness episode in which a ≥4-fold increase in antibody titer was observed (when preseason [obtained 30 days after vaccination] and postseason blood samples were compared) to vaccine or circulating influenza A or B strain, as determined by hemagglutination-inhibition assay.
A combined end point and the primary study end point, defined as a symptomatic influenza episode that was laboratory-confirmed as influenza by virus isolation in culture or by serologic analysis, as defined above.
A combined end point, defined as a symptomatic influenza episode that was laboratory-confirmed as influenza by isolation in culture, identification by real-time PCR, and/or serologic analysis, as defined above.