Protein conjugate polysaccharide vaccines: challenges in development and global implementation.

Pneumonia and meningitis caused by Haemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis are among the leading causes of under five mortality and morbidity. Polysaccharide vaccines to prevent these infections are available since 1980s, but these are not effective in infants and children who are the common targets; therefore, protein conjugated were developed. The aim of this article is to understand the need for peumococcal protein conjugate vaccines, the challenges related to their development and global implementation, and the impact of these vaccines on global child health. Challenges in development of new vaccines are as follows:While pneumonia is a major threat in developing countries, available vaccine 7-valent pneumococcal conjugate vaccine (PCV7) protects against only 30% of invasive disease.Serogroup B of Neisseria meningitidis causes 32% of the cases in the USA and 45-80% or more in Europe. Due to similarity of its capsular polysaccharide with the cell surface glycoprotein on fetal brain tissue, developing a vaccine against this bacterium remains a challenge.Challenges in implementation are as follows:Replacement by nonvaccine serotypes;capsule switching;time duration of the antibody protective effect following vaccination;costs of the vaccines, programme costs, lack of knowledge of the disease burden, and targeting population groups for vaccination.