Vaccine nationalism could increase the number of COVID-19 cases and the emergence of new variants

The allocation of the COVID-19 vaccine between countries has so far tended to vaccine nationalism, in which countries stock vaccines to prioritize access for their citizens rather than equitable sharing of vaccines.

The extent of vaccine nationalism, however, may have a significant impact on global trajectories of the number of COVID-19 cases and increase the potential emergence of new variants, according to a study by Princeton University and the University McGill published August 17 in the journal Science.

“Some countries like Peru and South Africa that have experienced severe COVID-19 outbreaks have received few vaccines, while many doses have gone to countries with relatively milder pandemic impacts, whether in terms of mortality or economic upheaval, ”said co-first author. Caroline Wagner, assistant professor of bioengineering at McGill University who was previously a postdoctoral research associate at the High Meadows Environmental Institute (HMEI) in Princeton.

“As expected, we have seen a sharp decrease in the number of cases in many areas with high access to vaccines, but infections are reappearing in areas with low availability,” said co-lead author Chadi Saad-Roy , Princeton graduate student in Ecology and Evolutionary Biology. and the Lewis-Sigler Institute for Integrative Genomics.

“Our goal was to explore the effects of different vaccine sharing programs on the global persistence of COVID-19 infections – as well as the possibility of evolving new variants – using mathematical models,” Saad said. -Roy.

Researchers projected the incidence of COVID-19 cases across a range of vaccine dosing regimens, vaccination rates, and hypotheses related to immune responses. They did this in two model regions: one with high access to vaccines – a high access region (HAR) – and a low access region (LAR). The models also made it possible to couple the regions either by importing cases or by developing a new variant in one of the regions.

“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,” said Wagner.

Overall, the study found that increased vaccine sharing resulted in a reduction in the number of cases in ARL. “Because vaccines appear to be very effective in reducing the clinical severity of infections, the public health implications of these reductions are very significant,” said co-author Michael Mina, assistant professor at Harvard TH Chan School of Public Health.

Lead author C. Jessica E. Metcalf, associate professor of ecology and evolutionary biology and public affairs at Princeton and associate professor at HMEI, added: Highly vaccinated populations.

The authors also drew on a framework developed in their previous work to begin trying to quantify the potential for viral evolution in different vaccine sharing programs. In their model, repeated infections in individuals with partial immunity – either from a previous infection or from a vaccine – may result in the development of new variants.

“Overall, the models predict that a high number of cases in LARs with limited vaccine availability will lead to a high potential for viral progression,” said lead author Bryan Grenfell, professor of ecology and science. Evolutionary Biology and Public Affairs of Princeton Kathryn Briger and Sarah Fenton. a faculty member associated with HMEI.

“As with our previous work, this study strongly underscores how important the rapid and equitable global distribution of vaccines is,” said Grenfell. “In a plausible scenario where secondary infections in individuals who have previously been infected strongly contribute to viral progression, uneven allocation of vaccines appears particularly problematic. “

As the pandemic progresses, viral evolution may play an increasingly important role in sustaining transmission, said lead author Simon Levin, distinguished professor at James S. McDonnell University of Princeton in Ecology and Evolutionary Biology and Associate Faculty Member of HMEI. “In particular, the antigenically new variants have the potential to threaten vaccination efforts around the world through several mechanisms,” he said, “including higher transmissibility, reduced vaccine efficacy or immune evasion. “

Saad-Roy added, “In this way, global vaccine coverage will reduce the clinical burden of new variants, while also decreasing the likelihood that these variants will emerge. “

There are additional considerations for vaccine equity beyond epidemiological and evolutionary considerations, said co-author Ezekiel Emanuel, University professor Diane vS Levy and Robert M. Levy and co-director of the Healthcare Transformation Institute of the ‘University of Pennsylvania.

“Ethics are also against countries stocking vaccines or allocating doses for boosters,” Emanuel said. “This study strongly supports this ethical position showing that storage will harm global health.”

Co-author Jeremy Farrar, director of the Wellcome Trust, UK, said the timing of vaccines being shared is also likely to be critical: “In particular, parallel sharing is what matters most. impact, not in sequence. “