A randomized, double-blind, placebo-controlled trial to evaluate the prime-boost strategy for pneumococcal vaccination in adult liver transplant recipients

Background. The 23-valent pneumococcal polysaccharide vaccine (PPV23) is recommended for disease prevention in solid-organ transplant recipients, but it may have suboptimal immunogenicity. It may be possible to enhance immunogenicity by priming the recipient with the 7-valent pneumococcal conjugate vaccine (PCV7), followed by boosting with PPV23. Methods. We randomized adult liver transplant recipients to receive either (1) PCV7 followed by a PPV23 booster 8 weeks later (the primed group) or (2) placebo followed by a standard single dose of PPV23 (the unprimed group). Quantitative and functional antibody titers for 7 serotypes contained in both vaccines were measured at baseline, 8 weeks after enrollment, and 16 weeks after enrollment. Of 130 randomized patients, 113 completed the study. Results. At week 16, response to at least 1 serotype was seen in 48 (85.7%) of 56 and 52 (91.2%) of 57 patients for the primed and unprimed groups, respectively (P = not significant). The mean number of serotypes to have responded (+/- SD) was 3.7 +/- 2.3 and 4.4 +/- 2.2 for the primed and unprimed groups, respectively (P = not significant). Functional antibody titers, which were measured with use of the opsonophagocytic assay, were also similar in both groups. Conclusions. The immunogenicity of pneumococcal vaccination was not enhanced by the prime-boost strategy, compared with vaccination with PPV23 alone. Administration of a single dose of PPV23 should continue to be the standard of care for adult liver transplant recipients. Clinical trials registration. NCT00152802 (http://www.clinicaltrials.gov).