Vaccine stockpiling by nations could lead to increase in COVID-19 cases,
novel variant emergence, study finds

Date:
August 17, 2021
Source:
Princeton University
Summary:
The extent of vaccine nationalism, wherein countries stockpile
vaccines to prioritize access for their citizenry over equitable
vaccine sharing, may strongly impact global trajectories of COVID-19
case numbers and increase the potential emergence of novel variants,
according to a new study.



FULL STORY ==========================================================================
The allocation of COVID-19 vaccine between countries has thus far tended
toward vaccine nationalism, wherein countries stockpile vaccines to
prioritize access for their citizenry over equitable vaccine sharing. The extent of vaccine nationalism, however, may strongly impact global
trajectories of COVID-19 case numbers and increase the potential
emergence of novel variants, according to a Princeton University and
McGill University study published Aug. 17 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 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).

"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.

"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.

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. 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 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.

"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.



========================================================================== 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 co-author Michael Mina, an assistant professor at the Harvard
T. H. Chan School of Public Health.

Senior author C. Jessica E. Metcalf, a Princeton associate professor
of ecology and evolutionary biology and public affairs and associated
faculty in HMEI, added: "High case numbers in unvaccinated populations
will likely be associated with higher numbers of hospitalizations and
larger clinical burdens compared to highly vaccinated populations."
The authors also drew on a framework developed in their prior work to
begin trying to quantify the potential for viral evolution under different vaccine sharing schemes. In their model, repeat infections in individuals
with partial immunity -- either from an earlier infection or a vaccine --
may result in the evolution of novel variants.

"Overall, the models predict that sustained elevated case numbers in
LARs with limited vaccine availability will result in a high potential
for viral evolution," said senior author Bryan Grenfell, Princeton's
Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary
Biology and Public Affairs and an associated faculty member in HMEI.

"As with our earlier work, the current study strongly underlines how
important rapid, equitable global vaccine distribution is," Grenfell
said. "In a plausible scenario where secondary infections in individuals
who have previously been infected strongly contribute to viral evolution, unequal vaccine allocation appears particularly problematic." As the
pandemic progresses, viral evolution may play an increasingly large
role in sustaining transmission, said senior author Simon Levin,
Princeton's James S. McDonnell Distinguished University Professor in
Ecology and Evolutionary Biology and an associated faculty member in
HMEI. "In particular, antigenically novel variants have the potential
to threaten immunization efforts globally through several mechanisms,"
he said," including higher transmissibility, reduced vaccine efficacy,
or immune escape."


========================================================================== Saad-Roy added: "In this way, global vaccine coverage will reduce the
clinical burden from novel variants, while also decreasing the likelihood
that these variants emerge." There are additional considerations
for vaccine equity beyond epidemiological and evolutionary ones,
said co-author Ezekiel Emanuel, the Diane v.S. Levy and Robert M. Levy University Professor and co-director of the Healthcare Transformation
Institute at the University of Pennsylvania.

"Ethics also argues against countries stockpiling vaccines or allocating
doses for boosters," Emanuel said. "This study strongly supports that
ethical position showing that stockpiling will undermine global health." Co-author Jeremy Farrar, director of the Wellcome Trust, UK, said that
the timing of when vaccines are shared also is likely to be critical:
"In particular, sharing in parallel is what makes the greatest impact,
not in sequence." Additional co-authors of the study include Sinead
Morris, a postdoctoral research scientist at Columbia University who
received her Ph.D. in ecology and evolutionary biology from Princeton;
Rachel Baker, an associate research scholar in HMEI; Andrea Graham,
professor of ecology and evolutionary biology at Princeton and HMEI
associated faculty; Edward Holmes, an ARC Australian Laureate and
professor at the University of Sydney; and Oliver Pybus, professor of
evolution and infectious diseases at the University of Oxford.

The paper, "Vaccine nationalism and the dynamics and control of
SARS-CoV-2," was published online Aug. 17 by Science. The work was
supported by funds from the Natural Sciences and Engineering Research
Council of Canada, the Cooperative Institute for Modeling the Earth
System at Princeton University, the James S. McDonnell Foundation,
the C3.ai Digital Transformation Institute and Microsoft Corporation,
Google, the National Science Foundation, the US Centers for Disease
Control and Prevention, and Flu Lab.

========================================================================== Story Source: Materials provided by Princeton_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Caroline E. Wagner, Chadi M. Saad-Roy, Sinead E. Morris, Rachel
E. Baker,
Michael J. Mina, Jeremy Farrar, Edward C. Holmes, Oliver
G. Pybus, Andrea L. Graham, Ezekiel J. Emanuel, Simon A. Levin,
C. Jessica E. Metcalf, Bryan T. Grenfell. Vaccine nationalism
and the dynamics and control of SARS-CoV-2. Science, 2021; DOI:
10.1126/science.abj7364 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210817152552.htm

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