SG sees drop in paediatric pneumococcal disease burden

The introduction of pneumococcal conjugate vaccines (PCV) into Singapore's National Childhood Immunisation Schedule (NCIS) has reduced the incidence of invasive pneumococcal disease (IPD) in children by nearly a third, as reported in a study.

Analysis of data from the KK Women's and Children's Hospital showed that the mean incidence of IPD decreased from 4.7 per 100,000 children between 2000–2009 (period 1) to 3.2 per 100,000 between 2010 and 2023 (period 2) (incidence rate ratio [IRR], 0.7, 95 percent confidence interval [CI], 0.6–0.8; p<0.001). [Open Forum Infect Dis 2025;12:ofaf093]

This overall reduction was primarily driven by a significant decline in IPD incidence among children in the younger age groups: from 13.3 to 4.7 per 100,000 among those ≤2 years (IRR, 0.4, 95 percent CI, 0.3–0.5; p<0.001) and from 15.2 to 8.9 per 100,000 among those between 2.1 and 5.0 years (IRR, 0.60, 95 percent CI, 0.5–0.7; p<0.001).

On the other hand, the incidence of IPD among children >5 years of age remained low and nearly unchanged, from 1.2 to 1.6 per 100,000 (IRR, 1.2, 95 percent CI, 0.9–1.7; p=0.11).

Pneumococcal serotypes

“PCV formulations contain a limited number of the >100 known serotypes, and nonvaccine types may replace vaccine serotypes in the upper airway, causing disease. This phenomenon of serotype replacement has led to the development of higher-valency PCVs after PCV7, such as PCV10, PCV13, and, more recently, PCV15 and PCV20,” the investigators said. [Vaccine 2018;36:6883-6891; Paediatr Drugs  2023;25:613-619]

In Singapore, PCV7 was available in the private sector from 2005 to 2009, but uptake remained limited, with IPD incidence persisting at 14.8 per 100,000 between 2005 and 2007. Subsequently, PCV7 was incorporated into the NCIS, followed by a transition to PCV13 in 2011 to expand serotype coverage. National PCV coverage was >80 percent from 2017 to 2023. [https://isomer-user-content.by.gov.sg/3/c1701d39-189c-4494-bf6a-1ad2240b4779/childhood-immunisation-2012.pdf; Int J Infect Dis  2012; 16:e209–15; Ministry of Health 2011;MOH circular:MH34:55/2]

From period 1 to 2, the percentage of children with IPD due to PCV7 serotypes effectively decreased from 68.0 percent to 22.0 percent (odds ratio [OR], 0.1, 95 percent CI, 0.1–0.2; p<0.001) and IPD due to PCV13 serotypes from 80.5 percent to 70.2 percent (OR, 0.6, 95 percent CI, 0.4–0.9; p=0.03).

However, a marked increase in IPD due to ST3 and ST19A was observed despite both serotypes being included in PCV13. IPD due to ST3 rose from 1.0 percent in period 1 to 8.9 percent in period 2 (OR, 10.0, 95 percent CI, 2.2–50.0; p<0.001), while those caused by ST19A jumped from 6.5 percent to 38.7 percent (OR, 9.1, 95 percent CI, 4.8–16.7; p<0.001).

“ST19A contributed to a significant proportion of severe IPD cases requiring ICU care, thoracoscopic drainage, or chest drain insertions in our cohort. Rising nonsusceptibility of ST19A to conventional antibiotics such as penicillin and ceftriaxone was also observed,” the investigators noted.

ST19A's persistent threat

As is the case in the UK and Peru, ST19A continues to pose a challenge as a disease-causing serotype after PCV13 implementation locally. This trend is unlikely to be a result of the adoption of a vaccination schedule of two major doses plus one booster dose, considering evidence from previous systematic reviews showing that 2 + 1 and 3 + 1 schedules are both effective in reducing IPD incidence, and the contribution of varying schedules to breakthrough IPD is inconclusive, as the investigators pointed out. [Pediatr Infect Dis J 2014;33(suppl 2):S109-S118; https://terrance.who.int/mediacentre/data/sage/SAGE_Docs_Ppt_Oct2017/9_session_PCV/Oct2019_session9_PCV_PRIMEsummary.pdf]

“Ongoing transmission of ST19A despite high-population PCV coverage may indicate that higher antibody concentrations are needed to protect against carriage. As ST19A predominates in Singapore in the post-PCV13 era, it is important that future PCVs improve protection against this particular serotype,” they continued.

The investigators called for additional research and surveillance given that higher-valency vaccines (PCV15 and PCV20) may have lower predicted immunogenicity against ST19A as compared with PCV13 and to ensure that the introduction of these higher-valency vaccines in Singapore does not result in any further increase in the burden of ST19A IPD. [Can Commun Dis Rep 2024;50:35-39; Expert Rev Vaccines 2024;23:60-68]