Table 2.
Protective efficacy of cell- and egg-based trivalent inactivated influenza virus vaccines in adults
| Strains | TIVc (n = 3776a) | TIVe (n = 3638a) | Placebo (n = 3843a) | Vaccine efficacyb | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| TIVc vs. placebo | TIVe vs. placebo | |||||||||
| No. of cases | Attack rate (%) | No. of cases | Attack rate (%) | No. of cases | Attack rate (%) | % | Lower limit of 97.5% CIc | % | Lower limit of 97.5% CIc | |
| Antigenically matchedd(i.e. vaccine-like) strains | ||||||||||
| Overalle | 7 | 0.19 | 9 | 0.25 | 44 | 1.14 | 83.8** | 61.0 | 78.4* | 52.1 |
| A/H1N1 | 5 | 0.13 | 8 | 0.22 | 43 | 1.12 | 88.2** | 67.4 | 80.3* | 54.7 |
| A/H3N2f | 2 | 0.05 | 1 | 0.03 | 0 | 0 | ||||
| Bf | 0 | 0 | 0 | 0 | 1 | 0.03 | ||||
| Non-antigenically matchedg(i.e. non-vaccine-like) strains | ||||||||||
| Overall | 30 | 0.79 | 29 | 0.80 | 74 | 1.93 | 58.7 | 33.5 | 58.6 | 32.9 |
| A/H1N1 | 1 | 0.03 | 0 | 0 | 8 | 0.21 | 87.3 | 4.6 | 100 | 33.9 |
| A/H3N2 | 0 | 0 | 2 | 0.05 | 8 | 0.21 | 100 | 36.3 | 73.6 | − 30.1 |
| B | 29 | 0.77 | 27 | 0.74 | 59 | 1.54 | 50.0 | 17.5 | 51.7 | 19.4 |
| All culture-confirmed influenza | ||||||||||
| Overall | 42 | 1.11 | 49 | 1.35 | 140 | 3.64 | 69.5** | 55.0 | 63.0* | 46.7 |
| A/H1N1 | 6 | 0.16 | 10 | 0.27 | 57 | 1.48 | 89.3** | 73.0 | 81.5** | 60.9 |
| A/H3N2 | 6 | 0.16 | 12 | 0.33 | 25 | 0.65 | 75.6 | 35.1 | 49.3 | − 9.0 |
| B | 30 | 0.79 | 27 | 0.74 | 61 | 1.59 | 49.9 | 18.2 | 53.2 | 22.2 |
Results of V58P13 (NCT00630331) [19]. Efficacies of TIVc and TIVe exceeded the CBER efficacy criteria
CBER Center for Biologics Evaluation and Research, TIVc cell-based trivalent inactivated influenza virus vaccine, TIVe egg-based trivalent inactivated influenza virus vaccine
*p < 0.01, **p < 0.001 (adjusted p-values; p < 0.025 indicates a vaccine efficacy significantly larger than 40%)
aEfficacy per protocol population (participants who were evaluable during their individual 6-month surveillance period)
b(1 − relative risk) × 100
cSimultaneous one-sided 97.5% CIs for vaccine efficacy of TIVc or TIVe relative to placebo; efficacy success criterion was a lower limit > 40% (prespecified for overall analyses but not for individual strains [11])
dIsolates were considered matched if there was a ≤ 4-fold difference in titre of the isolate and the vaccine strain against a reference antiserum
ePrimary endpoint (overall vaccine efficacy of each vaccine relative to placebo) achieved for each vaccine [13, 19]; see success criterion above
fToo few cases to adequately assess vaccine efficacy [10, 11]
gIsolates were considered non-vaccine-like if the haemagglutination inhibition antibody titre was ≥ 1:8 against specific reference strain antisera