Navigating the Herd Immunity Surface: A Novel Framework for Optimising Epidemic Response Strategies

Background: The typical reaction strategy to an epidemic involves the implementation of various pharmaceutical (e.g., vaccination) and non-pharmaceutical interventions (e.g., social distancing) to reach the so-called "herd immunity threshold," ensuring that new surges of the epidemic dampen out. Aim: We introduce a novel concept: the "Herd Immunity Surface." Unlike traditional approaches, which focus on a single herd immunity threshold, our framework considers heterogeneous population classes, such as different age cohorts or geographical regions. Methods: We demonstrate that multiple herd immunity thresholds can achieve equivalent epidemic-dampening outcomes, even when resulting from different strategies (e.g., uniform vaccination vs. prioritizing the elderly, generalized vs. selective lockdowns, etc.). Results: This discovery opens the door to policy optimization, where the specific herd immunity threshold chosen becomes a strategic decision with profound economic, logistic, political, and ethical implications. Importantly, it facilitates informed decision-making regarding the selection of vaccination strategies, allowing for versatility in achieving effective epidemic control. Conclusions: Our study introduces the concept of the Herd Immunity Surface, offering a novel framework that transcends traditional epidemic response strategies. By highlighting the redundancy in achieving herd immunity, our research provides a foundation for optimizing policy decisions, particularly in the context of vaccination strategies, with far-reaching implications for public health and policymaking.