Immunogenicity in high-risk and immunocompromised children and adults

In the developing world, human immunodeficiency virus (HIV) is a major contributor to adult pneumococcal disease, while the contributions of diabetes, chronic cardiopulmonary disease, and the other high-risk conditions are unknown but likely to be significant and increasing. The assessment of vaccine efficacy for many of the less frequent immunocompromising conditions in conventional randomized controlled trials with clinical end points is impractical, and thus, immunogenicity studies combined with case control or postmarketing surveillance studies are the most practical way to assess vaccine effectiveness. Several studies evaluating pneumococcal conjugate vaccine (PCV) in HIV-infected infants and older children have been published, including the only clinical efficacy trial of the nine-valent PCV conjugated to CRM, a nontoxic mutant diphtheria toxin (PCV9-CRM), in South Africa. Children with sickle-cell diseases (SCD) in the United States and Western Europe are particularly susceptible to pneumococcal infection. Several investigators have reported failure to elicit protective responses to pneumococcal polysaccharide vaccine (PPSV) when administered prior to 2 years after the transplant. Chronic obstructive pulmonary disease (COPD) increases the risk of invasive pneumococcal disease (IPD) to up to 10 times that of the age-matched population.