Skip to main content

Table 3 Attack rates and TIV efficacy for ILI during the influenza season* (ATP 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

Trivalent inactivated split virus influenza vaccine

N = 4011

Placebo

N = 2003

Vaccine efficacy

      

%

95% CI†

p value †

Number of events

Number of subjects reporting at least one event

% Attack rate

Number of events

Number of subjects reporting at least one event

% Attack rate

 

LL

UL

 

254

240

6.0

120

113

5.6

-6.1

-33.8

15.5

0.642

  1. * Influenza season starts the first week with two culture confirmed cases in the area, and closes at the end of the last week with one culture confirmed case in the areas.
  2. † Two-sided Fisher Exact test, the 95% confidence intervals for vaccine efficacy was calculated using a conditional exact method.