Review on global disease burden of pneumonia in young children and pneumococcal vaccination policy

Abstract

Pneumonia is one of the top causes of deaths in children younger than 5 years of age. According to WHO estimation, globally there are nearly 2 millions young children who die from pneumonia every year, and more than 70% of these deaths occurred in Africa and Southeast Asia. Pneumonia caused by Streptococcus pneumoniae (also called pneumococcus) is a vaccine preventable disease, accounting for 39% of community-acquired pneumonia. There are two types of pneumococcal vaccines that are pneumococcal polysaccharide vaccine (PPV) and pneumococcal conjugate vaccines (PCV). The latter one is routinely advised for children younger than five years. The aims of this paper are to review the global disease burden caused by Streptococcus pneumoniae in children younger than 5 years and to gather vaccine program information globally. For narrative review and policy analysis, WHO websites, other websites of health organizations or institutions, and literatures from Pubmed were reviewed, using key words “children pneumonia”, “Streptococcus pneumoniae”, “pneumonia vaccine”, “pneumococcal conjugate vaccine ”, “PCV-7”, “7-valent PCV”, “PCV-13”, “13-valent PCV”. Numerous literatures have reported that obvious incidence decrease of invasive pneumococcal diseases (IPD) in young children after PCV vaccination. In July 2000 PCV-7 (“7-valent pneumococcal conjugate vaccine”) was incorporated into National Immunization Program (NIP) in United States. Although since then the incidence of IPD caused by vaccine-covered serotypes markedly decreased, those caused by non-vaccine-covered serotypes were found substantially increased. In February 2010, PCV-13 (“13-valent pneumococcal conjugate vaccine”) replaced PCV-7 in NIP in United States. With a wider range of serotypes, PCV-13 was expected to be more effective than PCV-7 in children under 5. Using modeling method, many scholars estimated that PCV-13 was likely to be more cost-effective in reported settings when herd immunity was taken into consideration. Schedule of vaccine was another issue that needs to be investigated. There are three schedules commonly adopted by health authorities: 2 primary doses with 1 booster dose (2p+1), and 3 primary doses with 1 booster (3p+1) or without 1 booster dose (3p+0). In individual report, it seems three schedules were all effective. From result of systematic review, more evidence supported to use 3p+0 schedule (and 3p+1 schedule). However, emerging evidences are in support of 2p+1 schedule tool. WHO recommended both 3p+0 and 2p+1 schedule. If the country with high incidence rate in young infant (less than 32 weeks) 2p+1 schedule may not provide adequate protection for special individual serotype. In addition 2p+1 schedule may also lead to lower antibody level between the second primary dose and the booster dose, but the booster dose could induce higher antibody level, which is important for protecting certain serotypes. Countries should consider local factors and choose suitable vaccine schedule accordingly. In terms of global PCV programs, around 80 countries have already added PCV into their NIP, 58 countries (30%) were planning to introduce the program; nevertheless remaining 51 countries (26%) of countries have no schedule to introduce it yet. Most countries that have implemented PCV programs were western industrialized countries. With support from Global Alliance for Vaccines and Immunization (GAVI), 15 eligible African countries have had routine PCV programs. Comparatively, in Asia, India and China, two countries with the largest population and largest number of IPD cases in the world, have no PCV program to the children. Even industrialized economies like Japan and Taiwan have not implemented yet. Asia was lagging behind for decades. PCV program needs to be prioritized in Asian countries. Asian governments should consider investing more in PCV programs (high-income countries) and/or cooperating with other organizations such as GAVI (low-income countries) to increase the coverage of PCVs in children under 5 and to protect them from pneumococcal diseases.