Vaccine nationalism may strongly impact global trajectories of Covid-19 case numbers and increase the potential emergence of novel variants, warn researchers.

A team of researchers from the US and Canada projected forward the incidence of Covid-19 cases under a range of vaccine dosing regimes, vaccination rates, and assumptions related to immune responses.

They did so in two model regions: One with high access to vaccines (HAR) and a low-access region (LAR). 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. The study is published in the journal Science.

“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 Caroline Wagner, Assistant professor of bioengineering at McGill University.

Overall, the study found that increased vaccine-sharing resulted in reduced case numbers in LARs.

“Because it appears that vaccines are highly effective at reducing the clinical severity of infections, the public health implications of these reductions are very significant,” said Michael Mina, Assistant Professor at the Harvard T.H. Chan School of Public Health.

On the other hand, the models predicted that sustained elevated case numbers in LARs with limited vaccine availability will result in a high potential for viral evolution, underlying the importance of rapid, equitable global vaccine distribution.

As the pandemic progresses, viral evolution may play an increasingly large role in sustaining transmission, the researchers said.

Further, they noted that there are additional considerations for vaccine equity beyond epidemiological and evolutionary ones.

“Ethics also argues against countries stockpiling vaccines or allocating doses for boosters. This study strongly supports that ethical position showing that stockpiling will undermine global health,” said Ezekiel Emanuel, Professor at the University of Pennsylvania.