Strategies for COVID-19 vaccination under a shortage scenario: a geo-stochastic modelling approach

TL;DR

This study uses a geo-stochastic SEIRS model to compare COVID-19 vaccination strategies under shortages, highlighting the effectiveness of targeted vaccination and mobility reduction, with implications for timing and isolation measures.

Contribution

It extends existing models by incorporating vaccination compartments and social behavior, providing a comparative analysis of vaccination strategies during shortages.

Findings

Targeted vaccination in densely populated areas is more effective.

Reducing mobility enhances immunization outcomes.

Timing vaccination campaigns considering immunity lapse improves effectiveness.

Abstract

In a world being hit by waves of COVID-19, vaccination is a light on the horizon. However, the roll-out of vaccination strategies and their influence on the pandemic are still open problems. In order to compare the effect of various strategies proposed by the World Health Organization and other authorities, a previously developed SEIRS stochastic model of geographical spreading of the virus is extended by adding a compartment for vaccinated people. The parameters of the model were fitted to describe the pandemic evolution in Argentina, Mexico and Spain to analyze the effect of the proposed vaccination strategies. The mobility parameters allow to simulate different social behaviors (e.g. lock-down interventions). Schemes in which vaccines are applied homogeneously in all the country, or limited to the most densely-populated areas, are simulated and compared. The second strategy is found to be more effective. Moreover, under the current global shortage of vaccines, it should be remarked that immunization is enhanced when mobility is reduced. Additionally, repetition of vaccination campaigns should be timed considering the immunity lapse of the vaccinated (and recovered) people. Finally, the model is extended to include the effect of isolation of detected positive cases, shown to be important to reduce infections.