Emily J. Doucette, Leah J. Ricketson, Luis Murguía-Favela, Nicola Wright, James D. Kellner
Although PCVs remain highly effective overall, serotypes 3 and 19F continue to account for a disproportionate number of breakthrough IPD infections. Breakthrough disease became more common during the later PCV13 era and was associated with pneumonia/empyema but not underlying comorbidities, suggesting serotype specific factors may play a greater role than host susceptibility. Continued surveillance is needed to monitor breakthrough disease and the impact of evolving pneumococcal vaccine programs.
BACKGROUND: Since the introduction of pneumococcal conjugate vaccines (PCV7 in 2002 and PCV13 in 2010) in Alberta, the overall burden of invasive pneumococcal disease (IPD) in children has declined. However, vaccine-type invasive pneumococcal disease (VT-IPD) continues to occur, including in vaccinated children. METHODS: The Calgary Area Streptococcus pneumoniae Epidemiology Research (CASPER) study is a prospective, population-based surveillance program capturing all IPD cases in the Calgary area. We compared clinical features and outcomes of 227 vaccinated children (<18 years, ≥2 PCV doses) with IPD between 2003 and 2024. Among these, 44 (19.4%) had breakthrough infection and 183 (80.6%) had non-vaccine-type IPD (NVT-IPD). RESULTS: In multivariable analysis, pneumonia/empyema (OR: 5.9, 95% CI: 2.3-14.6) and IPD between 2018 and 2024 (OR: 4.0, 95% CI: 1.2-13.5) were associated with breakthrough infections, whereas comorbidities were not. Serotypes 3 (included in PCV13) and 19F (included in PCV7 and PCV13) accounted for most breakthrough infections. During the late PCV13 era, over 25% of IPD cases were breakthrough infections. Immunologic evaluation of a subset of children with breakthrough disease was largely unremarkable. CONCLUSIONS: Although PCVs remain highly effective overall, serotypes 3 and 19F continue to account for a disproportionate number of breakthrough IPD infections. Breakthrough disease became more common during the later PCV13 era and was associated with pneumonia/empyema but not underlying comorbidities, suggesting serotype specific factors may play a greater role than host susceptibility. Continued surveillance is needed to monitor breakthrough disease and the impact of evolving pneumococcal vaccine programs.