BACKGROUND/OBJECTIVES: Policymakers in the UK are considering modifying the pneumococcal conjugate vaccination (PCV) program from a 2+1 to a 1+1 schedule. Our dynamic transmission model estimated an increase in invasive pneumococcal disease (IPD) in <2 year-olds due to the proposed schedule. This study builds upon previous work by investigating differential risk of IPD in those who do not receive the booster dose in the two schedules.
METHODS: An established transmission dynamic model was parameterized using UK serotype-specific IPD data and published literature to predict 5-year cumulative IPD incidence per 100,000. For children ages 1 - <2, IPD incident risk ratios (IRR) were calculated as the risk of IPD without a booster dose compared to no booster dose. These IRR were then compared between 2+1 and 1+1 schedules. Scenario analyses examined the impact of modeling assumptions and parameter uncertainty.
RESULTS: For a 2+1 schedule, the model predicted a 5-year cumulative IRR of VT IPD in 1 - <2 year-olds of 1.08 for those who miss the booster dose versus those receiving the booster dose. In a 1+1 schedule, this IRR was 1.37, a 27.3% relative increase compared to a 2+1 schedule. Scenario analyses found that effectiveness of a priming dose was the main driver of increased disease when individuals miss a booster, with relative increases ranging from 16.7% to 45.6%.
CONCLUSION: Results demonstrate continued use of a 2+1 schedule would provide greater IPD protection to younger populations than the proposed 1+1 schedule. This outcome is magnified if single priming dose effectiveness is lower than hypothesized. Policymakers should consider the decreased protection afforded to children who may be more likely to miss their booster dose.
