Safety and efficacy profile of conjugate vaccines: A review of published studies

Invasive diseases caused by Streptococcus pneumoniae, Neisseria meningitidis, or Haemophilus influenzae (H. influenzae), such as meningitis and bloodstream infections, are life-threatening conditions. Owing to the introduction of universal vaccination programs, the incidence of invasive diseases is decreasing worldwide. Nevertheless, individuals with underlying diseases or those who have undergone an organ or stem cell transplantation are at a high risk of these diseases due to a compromised immune system. Therefore, effective preventive measures are warranted for these high-risk populations. Conjugate vaccines (conjugation of bacterial capsular polysaccharides covalently linked to a protein carrier) were developed to elicit a stronger, long-lasting immune response compared with conventional capsular polysaccharide vaccines in a T-cell-dependent manner. The use of the 13-valent pneumococcal conjugate vaccine (PCV13) for the prevention of pneumococcal pneumonia in high-risk individuals is recommended in Europe and the United States, and their use has been implemented in some countries. This article summarizes the epidemiology of bacterial meningitis and invasive pneumococcal disease (IPD) in Japan; provides an overview of conjugate vaccines (PCV13 for pneumococcal pneumonia, quadrivalent meningococcal groups A, C, W-135, and Y conjugate vaccine for meningococcal meningitis, and H. influenzae type b [Hib] conjugate vaccine for Hib infection); and discusses the efficacy, immunogenicity, and safety of the conjugate vaccines as reported by published clinical trials.