The contribution of the case-control approach to vaccine evaluation: Pneumococcal and Haemophilus influenzae type B PRP vaccines.

Case-control studies have had an increasing role in the postlicensure evaluation of vaccine efficacy. We review the contribution of case-control studies to the evaluation of vaccines for Streptococcus pneumoniae (pneumococcus) and Haemophilus influenzae type b (Hib) and compare these studies with clinical trials of these vaccines. We located one clinical trial and eight case-control studies of Hib PRP vaccine efficacy and three clinical trials and four case-control studies of pneumococcal vaccine efficacy. The pooled estimate of Hib PRP vaccine efficacy based on the case-control studies (0.38, 95% CL = 0.15-0.55) was lower than the efficacy of the clinical trial conducted in Finland (0.8, 95% CL = 0.57-0.98). The pooled estimate of pneumococcal vaccine efficacy based on the case-control studies (0.56, 95% CL = 0.44-0.66) was also lower than the pooled efficacy of the South African clinical trials (0.79, 95% CL = 0.69-0.86). Although the clinical trials provided crucial evidence that these vaccines worked in selected international settings, the direct evidence of efficacy in the United States rests largely on the case-control results. The utility of the case-control approach is supported.