BACKGROUND: The 13-valent pneumococcal conjugate vaccine (PCV13) is the only PCV licensed to protect against serotype 3 in children. However, conflicting estimates exist of PCV13’s direct and indirect protection vaccine effectiveness (VE) for serotype 3.
OBJECTIVE: Our study examined the of PCV13 for serotype 3 using different assumptions for PCV13 direct and indirect VE to model trends in serotype 3 invasive pneumococcal disease (IPD) and comparing these to observed data from the United Kingdom (UK). Methods: A dynamic transmission model of the spread of pneumococcal carriage and development of IPD was used to fit pre-PCV13–modeled IPD incidence with observed data. To allow for comparison across scenarios, post-PCV13–modeled IPD incidence was fit to observed data using assumptions for three different scenarios: (scenario 1) serotype 3 as a nonvaccine serotype, (scenario 2) VE against serotype 3 IPD of 63.5% based on a recent meta-analysis, and (scenario 3) a model-estimated VE against serotype 3.
RESULTS: Post-PCV13 introduction, modeled 2017 and average annual serotype 3 IPD incidence were within 20% and 59% of observed values for scenarios 2 and 3, respectively, but deviated by >100% for scenario 1. For adults aged ≥65 years, modeled 2017 IPD incidence in scenario 1 differed from observed data by 16% versus roughly 8% in scenarios 2 and 3.
CONCLUSIONS: Observed data do not support a scenario of no serotype 3 VE, but rather a combination of direct protection among vaccinated children and a lower level of indirect protection among older adults. Policymakers should consider transmission dynamics when examining VE against covered serotypes.
