Skip to main content

Table 2 Attack rates and TIV efficacy for culture confirmed influenza in adults (total cohort for efficacy)

From: Challenge of conducting a placebo-controlled randomized efficacy study for influenza vaccine in a season with low attack rate and a mismatched vaccine B strain: a concrete example

Type of culture confirmed Trivalent inactivated split virus influenza vaccine
N = 4137
Placebo
N = 2066
Vaccine efficacy (1-RR)
  Number of cases % Attack rate Number of cases % Attack rate % 95% CI† P value †
       LL UL  
Any 28 0.7 18 0.9* 22.3 -49.1 58.5 0.433
Influenza A 6 0.1 4 0.2 25.1 -260.9 82.2 0.740
Influenza B 22 0.5 14 0.7 21.5 -65.9 61.6 0.481
  1. * Sample size calculation was based on expected attack rate of at least 4% in the placebo group
  2. † Two-sided Fisher Exact test, the 95% confidence intervals for vaccine efficacy was calculated using a conditional exact method.