Efficient vaccination strategies to reduce the epidemic mortality in population with heterogeneous fatality rate

Jhun, Bukyoung; Choi, Hoyun

An insufficient supply of effective SARS-CoV-2 vaccine in most countries demands an effective vaccination strategy to minimize the damage caused by the disease. Currently, many countries vaccinate their population in descending order of age to minimize the deaths caused by the disease; however, the effectiveness of this strategy needs to be quantitatively assessed. We employed the susceptible-infected-recovered-dead (SIRD) model to investigate various vaccination strategies. In complex network, the case fatality rate (CFR)-based method was shown to be more effective than the load-based strategy when there is a low supply of vaccine; however, when there is a sufficient quantity of vaccine, the load-based strategy is more effective than the CFR-based strategy. We also constructed a metapopulation model with empirical human contact and CFR data for SARS-CoV-2 and investigated vaccination strategies. We found that the age-based strategy, which is currently employed in many countries, is more effective when the basic reproduction number is high and vaccination supply is low, but the rate-based method outperforms the age-based strategy when there is sufficiently high supply of vaccine. Simulated annealing is performed to find the optimal vaccination strategy. We identified a first-order phase transition in the vaccination strategies which is characterized by discontinuous transition in the optimal strategy and the hysteresis. This phase transition implies that mixing the age-based and rate-based strategy is ineffective in reducing the number of deaths. These conclusions are valid even when the heterogeneous degree distribution of human contact is considered.