Modelling the Epidemiological Impact of Different Adult Pneumococcal Vaccination Strategies in the United Kingdom

Pneumococcal conjugate vaccines (PCVs) were first introduced in the paediatric United Kingdom (UK) immunisation programme in 2006 which led to significant declines in invasive pneumococcal disease (IPD) caused by targeted serotypes. Although paediatric PCVs provide some indirect protection to adults, a significant IPD burden remains in older adults. Here, we compared three adult (65+ years-old) and risk group (2–64-year-old) vaccination scenarios, namely a continuation of the status quo with PPSV23 vaccination, using the recently licensed-in-adults PCV20, or using the new adult-focused 21-valent PCV, V116. A population-level compartmental dynamic transmission model (DTM) was adapted to the UK setting. The model described Streptococcus pneumoniae carriage transmission dynamics and disease progression in the presence of age- and serotype-specific pneumococcal vaccines. We calibrated the DTM to age- and serotype-specific IPD data in the UK and used the model to make projections under the different adult vaccination scenarios while keeping PCV13 immunisation in children. The calibrated model yielded reasonable parameter values and model fits that closely matched observed IPD dynamics. Among 65+ year-olds, 10-year model projections predicted that the routine use of V116 would reduce IPD incidence by 15.5%, while PCV20 would reduce IPD incidence by 8.9% and the continued use of PPSV23 would increase incidence by 3.83%. There was a notable decrease in IPD incidence in the serotypes unique to V116. In the serotypes included in PCV20 but not V116, the model did not predict a resurgence of IPD. Projections revealed that in adults, V116 led to significantly greater reductions in IPD in the 65+ year-old population compared with PCV20 or PPSV23.