Understanding the impact of disease and vaccine mechanisms on the importance of optimal vaccine allocation

Abstract

AbstractVaccination is an important epidemic intervention strategy. Resource limitations and an imperative for efficient use of public resources drives a need for optimal allocation of vaccines within a population. For a disease causing severe illness in particular members of a population, an effective strategy to reduce illness might be to vaccinate those vulnerable with a vaccine that reduces the chance of catching a disease. However, it is not clear that this is the best strategy, and it is generally unclear how the difference between various vaccine strategies changes depending on population characteristics, vaccine mechanisms and allocation objective. In this paper we develop a conceptual mathematical model to consider strategies for vaccine allocation, prior to the establishment of community transmission. By extending the SEIR model to incorporate a range of vaccine mechanisms and disease characteristics, we simulate the impact of vaccination on a population with two sub-groups of differing characteristics. We then compare the outcomes of optimal and suboptimal vaccination strategies for a range of public health objectives using numerical optimisation. Our comparison serves to demonstrate that the difference between vaccinating optimally and suboptimally may be dependent on vaccine mechanism, diseases characteristics, and objective considered. We find that better resources do not guarantee better outcomes. Allocating optimally with lesser vaccine resources can produce a better outcome than allocating good vaccine resources suboptimally, dependent on vaccine mechanisms, disease characteristics and objective considered. Through a principled model-based process, this work highlights the importance of designing effective vaccine allocation strategies. This design process requires models that incorporate known biological characteristics, realistic parameters based on data analysis, etc. Overall, we see that allocation of resources can be just as crucial to the success of a vaccination strategy as the strength of resources available.