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Overall, the study found that increased vaccine-sharing resulted in reduced case numbers in LARs. "In this way, we could assess the dependence of our epidemiological projections on different immunological parameters, regional characteristics such as population size and local transmission rate, and our assumptions related to vaccine allocation," Wagner said. The models also allowed for the regions to be coupled either through case importation, or the evolution of a novel variant in one of the regions. They did so in two model regions: One with high access to vaccines - a high-access region (HAR) - and a low-access region (LAR). The researchers projected forward the incidence of COVID-19 cases under a range of vaccine dosing regimes, vaccination rates, and assumptions related to immune responses. "Our goal was to explore the effects of different vaccine-sharing schemes on the global persistence of COVID-19 infections - as well as the possibility for the evolution of novel variants - using mathematical models," Saad-Roy said.
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"As expected, we have seen large decreases in case numbers in many regions with high vaccine access, yet infections are resurging in areas with low availability," said co-first author Chadi Saad-Roy, a Princeton graduate student in ecology and evolutionary biology and the Lewis-Sigler Institute for Integrative Genomics. "Certain countries such as Peru and South Africa that have had severe COVID-19 outbreaks have received few vaccines, while many doses have gone to countries experiencing comparatively milder pandemic impacts, either in terms of mortality or economic dislocation," said co-first author Caroline Wagner, an assistant professor of bioengineering at McGill University who previously served as a postdoctoral research associate in Princeton's High Meadows Environmental Institute (HMEI).