BACKGROUND AND AIMS: PCVs have been successfully implemented in 3+1, 2+1, and 3+0 schedules. However, due to limited resources and crowded infant vaccination schedules a number of studies are ongoing to evaluate immunogenicity and effect on nasopharyngeal carriage of 1+1 PCV dosing schedule. Because of uncertainty of real-world impact of 1+1 schedule implementation, we modeled invasive pneumococcal disease (IPD) under 2+1 and 1+1 PCV13 schedules.
METHODS: A dynamic transmission model was built to simulate the effects of a 2+1 or a 1+1 schedule. The model was parameterized using UK serotype-specific invasive pneumococcal disease (IPD) surveillance data and published literature. The model was run prospectively to predict cumulative differential impact of each schedule on IPD incidence. Scenario analyses were undertaken to examine impact of model assumptions and parameter uncertainty around vaccine effectiveness, implementation, and population dynamics.
RESULTS: Compared with a 2+1 schedule over 5 years, reducing to a 1+1 schedule resulted in 87 to 231 more cases of IPD in the UK corresponding to a 22% – 50% increase in vaccine-type IPD in <2 year-olds. Scenario analyses suggest that effectiveness of a 1+1 schedule to impact nasopharyngeal carriage and maintain the herd effect has the most substantial impact on results.
CONCLUSION: The results demonstrate continued use of a 2+1 schedule would provide a greater public health benefit compared to switching to 1+1. Policy makers should consider the uncertainty of clinical effects of a 1+1 schedule when considering modifications to a successful vaccine program.
