In March 2015, Bangladesh introduced the 10-valent pneumococcal conjugate vaccine (PCV10) to combat invasive pneumococcal disease (IPD) and severe pneumonia in children. This study assesses the vaccine’s impact on both IPD and clinically identified severe pneumonia among children aged 2 to 24 months in the rural sub-district of Mirzapur, Bangladesh. It also evaluates the vaccine’s effectiveness against invasive disease caused by vaccine serotypes through population-based surveillance.

The study used two complementary designs. First, a before-after study was conducted in Mirzapur to compare the incidence of IPD and severe pneumonia before (April 2012 to March 2015) and after (April 2015 to March 2019) the introduction of PCV10. Second, an indirect cohort study was carried out across four sentinel sites to estimate the vaccine’s effectiveness against IPD caused by vaccine serotypes.

Population-based surveillance in Mirzapur was key to gathering data. The Kumudini Women’s Medical College Hospital (KWMCH), the largest non-profit private hospital in Bangladesh, served as the main healthcare facility for the surveillance. Trained Village Health Workers (VHWs) referred children with symptoms of pneumonia, suspected sepsis, or meningitis to KWMCH for further evaluation, including blood cultures to detect pneumococcal infections.

The study enrolled 20,187 children, of whom 3,395 were monitored in the pre-vaccine period and 16,792 in the post-vaccine period. Overall, these children contributed 34,608 child-years of observation.

In children under two, the incidence of IPD decreased by 25% following PCV10 introduction, from 106.1 cases per 100,000 child-years before the vaccine to 79.3 cases in the post-vaccine period. While the overall decline was not statistically significant (95% CI: −1.2% to 76%, p = 0.59), a notable 77% reduction in IPD caused by vaccine serotypes was observed (from 85.7 to 19.8 cases per 100,000 child-years; p = 0.068). However, cases caused by non-vaccine serotypes (NVT-IPD) increased from 10.9 to 44.5 cases per 100,000 child-years, though this rise was not driven by any specific serotype.

The incidence of severe pneumonia decreased significantly, with a 54% reduction (p < 0.001) observed after PCV10 introduction. At baseline, the crude incidence of severe pneumonia was 50.1 per 1,000 child-years, which dropped to 33.8 per 1,000 child-years by the fourth year of post-vaccine observation. Adjusted rates showed even greater reductions, falling from 97.4 to 45.2 cases per 1,000 child-years.

An indirect cohort analysis of data from four sentinel sites, including Mirzapur, showed that the effectiveness of PCV10 after the first dose was 37% (95% CI: −141% to 83%, p = 0.49). After two or three doses, vaccine effectiveness increased to 63% (95% CI: 3.3% to 85.9%, p = 0.0411), providing stronger protection against vaccine serotype IPD.

This study demonstrates that PCV10 has contributed to a significant reduction in severe pneumonia hospitalisations and provided substantial protection against vaccine serotype IPD among children under two years of age in Bangladesh. However, the increase in non-vaccine serotype IPD highlights the need for ongoing surveillance and potentially broader vaccines to address emerging pneumococcal strains.

Reference:
Malakar, R. et al, Effectiveness of ten-valent pneumococcal conjugate vaccine on invasive pneumococcal disease among children <2 years old: A prospective population-based study in rural Bangladesh. Vaccine, Volume 42, Issue 2, 2024, Pages 255-262, Sciencedirect.com. [cited 2024 Oct 20]. Available from: https://www.sciencedirect.com/science/article/pii/S0264410X23014408#s0060