Seven studies (n not reported in some instances) were included in the review. One study was a single-blind placebo controlled RCT, two were open-label CCTs and four were retrospective cohort studies.
The single RCT (n not reported) was terminated early after a statistically significant difference (statistics not reported) between the groups. This was based on seven cases of Q fever in the non-vaccinated group versus 0 cases in the vaccinated group.
The efficacy of the vaccine in the two CCTs was 92% in each case (95% CIs 42% to 99% and 70% to 98%).
Efficacy in the cohort studies ranged from 83% to 100%.