Studies from Belgium, Spain, and the United States highlight that vaccine failures in young children are uncommon but linked to specific serotypes, underscoring the need for ongoing surveillance as newer vaccine formulations are introduced.
Pneumococcal vaccine failure in young children appears to be uncommon, but researchers say continued tracking will be essential as newer formulations are rolled out. A study published in Vaccine found that among Belgian children aged 0 to 5 years during the PCV13 era from 2019 to 2024, just 5.8% of vaccinated children had vaccine failures and 8.2% experienced breakthrough infections. The cases were mainly linked to serotypes 19A, 3 and 14, and were more often seen in older children with invasive pneumonia.
That Belgian analysis fits a broader pattern seen in earlier research. A narrative review in Vaccines said residual vaccine-type pneumococcal disease still occurs despite large childhood immunisation programmes, with serotype 3 standing out as a persistent challenge. The review noted that standard antibody thresholds used for vaccine licensure do not fully capture the stronger immune response needed to protect against serotypes 3 and 19A, which may help explain why those strains keep appearing in breakthrough cases.
Evidence from Spain points in the same direction. A prospective paediatric study published in Emerging Infectious Diseases found 24 vaccine failure cases between 2012 and 2016, with complicated pneumonia, including empyema, the most common presentation. The Spanish researchers said most diagnoses were confirmed by polymerase chain reaction, not culture, reflecting how often antibiotics make traditional testing come back negative in children.
Longer-term data from the United States suggest these events remain rare at the population level. A Pediatrics study covering 2001 to 2016 found breakthrough infections were uncommon overall, although children who received a two-dose primary series without a booster had higher rates in the first year of life than those who received three primary doses. The findings have helped inform ongoing review by the Advisory Committee on Immunization Practices, while CDC guidance also stresses that administration errors, such as doses given too close together, can undermine protection. Against that backdrop, the Belgian study offers a useful benchmark for PCV20 and future higher-valent vaccines, where researchers say surveillance will be needed to see whether the newer products close the remaining gaps.
Disclaimer: This content is for informational purposes only and is not intended to be a substitute for professional medical judgment, advice, diagnosis, or treatment.
