Streptococcus pneumoniae, commonly known as pneumococcus, is associated with significant morbidity and mortality worldwide. This pathogen is notorious for causing invasive pneumococcal disease (IPD) along with various non-invasive diseases, impacting particularly vulnerable populations such as young children and the elderly. With over 98 known serotypes, the development and administration of vaccines that cater to the diversity of these serotypes are critical for public health.

In Thailand, the challenge of pneumococcal disease prevention takes on additional layers of complexity. Despite the global burden of pneumococcal diseases and the existence of pneumococcal conjugate vaccines (PCVs), Thailand’s National Expanded Programme of Immunization (EPI) did not have a PCV in its schedule at the time of this particular study. A systematic review led by researchers Rebecca E. Hocknell, David W. Cleary, Somporn Srifeungfung, and Stuart C. Clarke aimed to highlight the serotype distribution of disease-causing Streptococcus pneumoniae in Thailand to inform potential vaccine implementation strategies.

Published in the journal Vaccine (DOI: 10.1016/j.vaccine.2019.04.085), this systematic review meticulously gathered data from the NCBI PubMed database and Google Scholar to identify relevant papers published between January 1st, 1990, and August 21st, 2017. They found 15 relevant articles that shed light on the prevalence of pneumococcal serotypes associated with IPD and non-invasive pneumococcal diseases in the country.

The distribution of serotypes was categorized into two age groups: ≤5 years old and >5 years old, as these were the most commonly reported parameters. However, when age demographics were not clearly stated, or the data was combined, the researchers categorized the results as encompassing all ages. Through these collected studies, they identified the five most prevalent disease-causing serotypes in Thailand to be, in descending order of frequency, 6B, 23F, 14, 19A, and 19F.

It was argued that if PCV10 (Synflorix®) or PCV13 (Prevnar 13®) vaccines were introduced to the Thai public health program, vaccine coverage would be 55.3% for PCV10 and 69.7% for PCV13. While these numbers indicate a substantial portion of the population would be protected, there’s still a shortage of data concerning non-invasive disease-causing pneumococcal serotypes. In light of this, the comprehensive surveillance of both IPD and non-IPD is necessary to fully assess vaccine effectiveness should PCVs be integrated into Thailand’s national immunization agenda.

The call for better surveillance data stems from the need to ensure that the selected vaccines are effectively targeting the serotypes that are most prevalent and causing disease. This is crucial in a country like Thailand, where monetary and healthcare resources must be allocated judiciously. With a well-structured surveillance system, it would be possible to monitor the changes in serotype distribution post-vaccination, a phenomenon known as serotype replacement. This occurrence is where non-vaccine serotypes potentially fill the ecological niche left by vaccine-targeted serotypes, potentially leading to a shift in the epidemiology of the disease.

The authors of the study point out several implications of their findings. Establishing a comprehensive pneumococcal vaccination program could significantly curb the rates of morbidity and mortality in Thailand, especially amongst the most vulnerable children under five years of age. Additionally, the insights from this review are instrumental in the argument for including PCVs in Thailand’s EPI schedule. This systematic review has laid the groundwork for a data-driven approach to fighting pneumococcal diseases in Thailand.

In conclusion, while the systematic review by Hocknell and colleagues sheds light on the predominant pneumococcal disease-causing serotypes in Thailand, it also calls attention to gaps in the existing data and the need for an enhanced surveillance system. With global health efforts directed toward the prevention of pneumococcal diseases, research such as this plays a pivotal role in shaping vaccination policies and ultimately reducing disease burden.

References

1. Hocknell, R. E., Cleary, D. W., Srifeungfung, S., & Clarke, S. C. (2019). Serotype distribution of disease-causing Streptococcus pneumoniae in Thailand: A systematic review. Vaccine, 37(24), 3159-3166. doi: 10.1016/j.vaccine.2019.04.085
2. World Health Organization. (2021). Pneumococcal vaccines WHO position paper – March 2021. Retrieved from https://www.who.int/news-room/feature-stories/detail/pneumococcal-vaccines-who-position-paper—march-2021
3. Centers for Disease Control and Prevention. (2020). Pneumococcal Vaccination: What Everyone Should Know. Retrieved from https://www.cdc.gov/vaccines/vpd/pneumo/public/index.html
4. Global Burden of Disease Study collaborators. (2018). Global, regional, and national age-sex-specific mortality for 282 causes of death, 1980–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet, 392, 1736-1788. doi: 10.1016/S0140-6736(18)32203-7
5. Weiser, J. N., Ferreira, D. M., & Paton, J. C. (2018). Streptococcus pneumoniae: transmission, colonization and invasion. Nature Reviews Microbiology, 16(6), 355-367. doi: 10.1038/s41579-018-0001-8

Keywords

1. Pneumococcal Vaccines Thailand
2. Streptococcus Pneumoniae Serotypes
3. Pneumococcal Conjugate Vaccine (PCV)
4. Invasive Pneumococcal Disease (IPD)
5. National Expanded Program Immunization (EPI) Thailand