Invasive pneumococcal disease among children under five years of age in Southern Vietnam: Epidemiology and Vaccine Effectiveness
(2026)
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- Abstract
- Pneumococcal disease remains one of the leading causes of morbidity and mortality among children under five years of age worldwide, particularly in low- and middle-income countries (LMICs). Streptococcus pneumoniae is responsible for a broad spectrum of clinical manifestations ranging from non-invasive illnesses such as pneumonia and otitis media to severe, life-threatening invasive pneumococcal diseases (IPD), including meningitis and bacteremia. Although pneumococcal conjugate vaccines (PCVs) have substantially reduced IPD incidence in many high-income settings, gaps in local data, limited surveillance capacity, and delayed vaccine introduction continue to hinder their optimal use in LMICs. In Vietnam, where Hib vaccination has virtually eliminated Haemophilus influenzae type b meningitis, S. pn has become the dominant bacterial pathogen causing meningitis in young children. This thesis provides the first comprehensive investigation into the burden, microbiological characteristics, and real-world vaccine effectiveness of PCVs in Vietnamese children under five years of age. Using a multidisciplinary approach, it integrates (i) a ten-year retrospective hospital-based surveillance study to describe long-term epidemiological trends of bacterial meningitis, (ii) clinical and microbiological analyses of pneumococcal meningitis to determine clinical characteristics, serotype distribution, and antibiotic resistance genes, and (iii) a three-year matched case-control study assessing the effectiveness of PCV against IPD in real-world conditions. Together, these components offer a detailed picture of pneumococcal disease dynamics in Vietnam from the post-Hib period to the pre-national PCV introduction era. The findings demonstrate that S. pneumoniae accounts for over 85% of confirmed bacterial meningitis cases in Vietnamese children. Serotypes 6A/B, 19F, and 19A predominate, with more than 75% of IPD cases attributable to serotypes included in current PCV10 and PCV13 formulations. However, a steady rise in non-vaccine serotypes, particularly 15A/F, 11A/D, and 23A, was observed over time, suggesting early signs of serotype replacement. Molecular analysis revealed alarmingly high antibiotic resistance rates to macrolide (87.6%), tetracycline (92.0%), and penicillin (68.6%). The resistance levels are consistent with reports from several high-burden settings, including Zambia (2010-2019), central Vietnam (2015-2016), and China (2014-2016), and are higher than those observed in some high-income countries, such as France (2001-2022), Israel (2004-2016), and the United States (2007-2009). Despite these challenges, PCVs demonstrated strong real-world protection, even under conditions of limited coverage and mixed vaccine use, reinforcing their potential to substantially reduce IPD burden in Vietnam. The implications of these findings extend beyond disease prevention. Introducing PCV13 into the national Expanded Program on Immunization (EPI) will not only prevent invasive bacterial infections and pneumonia-related hospitalizations but also indirectly contribute to controlling antibiotic resistance by reducing unnecessary antibiotic use. The results provide a robust, evidence-based foundation for national policy decisions regarding vaccine introduction, schedule optimization, and long-term disease surveillance. Ultimately, this thesis bridges a critical evidence gap in the Western Pacific by generating locally relevant data that inform global pneumococcal control strategies. It highlights the importance of integrating vaccination, molecular diagnostics, and antibiotic stewardship to achieve sustainable prevention of pneumococcal disease. The insights gained from this research will support Vietnam’s forthcoming introduction of PCV13 into the national EPI from 2026 onwards and serve as a model for other LMICs seeking to strengthen vaccine policy through locally driven scientific evidence.
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Truong, H. (2026). Invasive pneumococcal disease among children under five years of age in Southern Vietnam: Epidemiology and Vaccine Effectiveness. https://hdl.handle.net/2078.5/272886