Few vaccine failures with 10-valent pneumococcal conjugate vaccine in children, Finland, 2010-2025

Abstract Background Invasive pneumococcal disease (IPD) is a major cause of communicable disease burden in Europe and globally. Pneumococcal vaccines cover common IPD serotypes; vaccine failures should be monitored to follow-up National Vaccination Programmes (NVPs). In Finland, the 10-valent pneumococcal conjugate vaccine (PCV10) was included in the NVP with a 2 + 1 schedule in 09/2010 for children born since 06/2010. We performed a retrospective register-based study of IPD among PCV10 eligible children to identify vaccine failures and breakthrough cases. Methods We retrieved notified IPD cases during 09/2010-02/2025 in children born after 01/06/2010 from the National Infectious Diseases Register, and their PCV10 vaccination status from the National Vaccination Register. Vaccine failure was defined as PCV10 serotype IPD in a fully vaccinated child (3 doses) and vaccine breakthrough infection as PCV10 serotype IPD in a child who had received 1-2 doses of PCV10 ≥14 days before a positive laboratory test. Results Among 441 IPD cases, serotypes were available for 428 (97%); of these, 361 (84%) were partially (n = 92) or fully (n = 269) vaccinated prior to diagnosis. Among those, the most common serotypes were non-PCV10 serotypes 19A (n = 183), 3 (n = 55), 6C (n = 17), 22F (n = 16), and 23B (n = 14). We identified nine vaccine failures and six vaccine breakthrough cases, i.e. 3.3% and 6.5% of the fully and partially vaccinated IPD cases, respectively. Vaccine failures were serotypes 6B (n = 4), 19F (n = 2), 23F (n = 2), and 14 (n = 1). Vaccine breakthrough cases were serotypes 19F (n = 2), 23F (n = 2), 7F (n = 1), and 1 (n = 1). Most vaccine failure (7/9) and breakthrough (4/6) cases were female, all were <5 years of age. 5/6 breakthrough cases had received one PCV10 dose. Conclusions Vaccine failures and breakthroughs were rare, indicating success of the NVP. Higher-valency vaccines cover the most common IPD serotypes in partially and fully vaccinated children, which has informed an upcoming NVP change to PCV13. Key messages • Vaccine failures and breakthroughs were rare after more than 14 years of 10-valent pneumococcal conjugate vaccine use in the national vaccination programme for children in Finland. • Higher-valency conjugate vaccines cover the most common IPD serotypes in partially and fully vaccinated children. This has informed an upcoming national vaccination programme change.