A modeling study has warned that vaccine hoarding by countries could have a significant impact on global trajectories of Covid case numbers, as well as the potential introduction of novel viral strains. Using mathematical models, the researchers investigated the implications of various vaccine-sharing strategies on the global persistence of Covid infections, as well as the likelihood of the emergence of new varieties.
According to the researchers, COVID-19 preventative vaccine distribution has leaned toward vaccine nationalism, with countries stockpiling vaccines to prioritize access for their population over equitable vaccine sharing.
“Some countries with severe COVID-19 outbreaks have received few vaccines, while many doses have gone to countries with comparatively milder pandemic impacts, either in terms of mortality or economic dislocation,” said Caroline Wagner, an assistant professor at McGill University in Canada, who was a study, co-first author.
“As expected, we’ve seen huge drops in case of numbers in many locations with high vaccination access, but infections are resurging in areas with limited availability,” said Chadi Saad-Roy, a Ph.D. student at Princeton University in the United States.
The researchers calculated the likelihood of Covid cases using a variety of vaccine dosage regimens, immunization rates, and immune response assumptions.
They did so in two model regions: one with high vaccine access, known as a high-access region (HAR), and another with low vaccine access, known as a low-access region (LAR) (LAR).
The models also allowed for the coupling of regions via case importation or the generation of a novel variant in one of the regions.
Increased vaccine sharing led to fewer cases in LARs, according to the study.
“Because vaccines appear to be highly effective at reducing the clinical severity of infections, the public health implications of these reductions are very significant,” said Michael Mina, an assistant professor at Harvard TH Chan School of Public Health in the United States, and co-author of the study.
According to Jessica Metcalf, a Princeton associate professor, high case numbers in unprotected communities will likely be associated with more hospitalizations and heavier clinical burdens than fully vaccinated populations.
The researchers also used a framework they built before to estimate the potential for virus evolution under various vaccine sharing strategies.
According to their model, repeated infections in individuals with limited immunity – either from a previous infection or from a vaccination – resulted in the emergence of novel variations.
“Overall, the models imply that sustained increasing case counts in LARs with limited vaccination availability will result in a significant potential for viral evolution,” said research senior author Bryan Grenfell of Princeton’s High Meadows Environmental Institute (HMEI).
“The study emphasizes the importance of timely and fair global vaccination distribution,” Mr. Grenfell added.
In a scenario where secondary infections in previously infected individuals play a significant role in virus development, unequal vaccine allocation looks to be particularly troublesome, according to the researchers. They said that having a global vaccine coverage will lessen the clinical burden of novel variants while also lowering the likelihood of these variants developing.