Figure 2. Relative odds of shedding vaccine poliovirus after challenge among individuals vaccinated with OPV compared with unvaccinated individuals.

Odds ratios (ORs) and 95% confidence intervals for individual studies are indicated by the boxes and grey lines. The summary odds ratio for each serotype is given by a diamond with the 95% confidence interval (CI) indicated by its width. The χ² test for heterogeneity among studies was significant for serotypes 2 and 3 (p-values 0.33, <0.001, and 0.001 for serotypes 1, 2, and 3, respectively) and for the overall odds ratio (p-value<0.001). Details of the studies included are given in Table S1. *Ghendon et al. 1961 [17] compare vaccinated and unvaccinated children who were confirmed seropositive and seronegative, respectively.