Science & Technology

Vaccine stockpiling may do more harm than good

While the high vaccination rate among certain portions of the population has lifted public health restrictions and allowed some semblance of normalcy, the COVID-19 pandemic is far from over. Despite vaccine administration having begun in December 2020, only 37 per cent of the world’s population has received both doses, with high-income countries comprising the highest proportion of vaccinated people.

In a recent study, a team of researchers, including scientists from McGill, ran simulations that explored the impact of vaccine stockpiling by wealthy countries on infection rates in low- and middle-income countries.

Caroline Wagner, an assistant professor in McGill’s Department of Bioengineering and co-first author of the study, explained that the team was motivated to see if there was scientific evidence behind the claim that vaccine nationalism causes harm. 

“I think you can argue against [vaccine stockpiling] on purely ethical grounds, and people have, but we also wanted to think scientifically [about] what the implications might be,” Wagner said in an interview with The McGill Tribune.

The researchers simulated the expected number of infections in two hypothetical regions—one with high access to vaccines and the other with low access—using assumptions based on characteristics like vaccination rates, the strength and duration of natural and vaccine immunity, cross-border transmission, and the potential increase in infections due to viral evolution.

The results showed that in the case of limited vaccine supply, vaccine stockpiling by high-availability regions leads to increased infections in low-availability regions. There is also more potential for the virus to evolve into more contagious variants as the number of infections increases.

“Allowing infections to circulate widely, which is going to be of particular concern in unvaccinated populations, is particularly bad for the potential for viral evolution because every time the virus replicates, mutations can arise,” Wagner said. “If the virus evolves to a point where it can then evade our acquired immunity, then all the efforts to heavily vaccinate a certain region might be futile if a variant comes up that can evade the immunity conferred by that vaccine in the first place.”

In recent months, several new variants of the virus have emerged, such as Delta, Gamma, and Alpha. These variants are more contagious than the original virus and have the capacity to infect vaccinated people. Equitable global vaccine sharing, Wagner explained, would decrease the burden on the health care system in low-income countries and minimize evolution of the COVID-19 virus. 

“The vaccines are not perfect, there are breakthrough infections,” Wagner said. “But by and large, they are super effective at mitigating serious disease. Even if we don’t totally eliminate infections, if we can decrease the clinical burden of this disease around the world through vaccination, that’s very important. Especially in regions which might have less robust health care systems.”

The team presented their research to the World Health Organization and other health policy makers across different countries to encourage them to adopt a global perspective instead of solely considering their country’s interests. In the long run, with cross-border transmission of the new variants, increasing the number of vaccinated people globally would benefit individual countries. 

The team’s current model simulates the effect of vaccine stockpiling in two hypothetical regions. Moving forward, the researchers want to incorporate real-world data and are currently working on a model specific to Canada.

As scientists and policymakers explore the possibility of additional “booster” doses, it becomes increasingly important to consider trade-offs between the benefits gained from a booster shot and the continued viral evolution and harm caused to more than half of the world’s unvaccinated population.

“Everyone is talking about boosters now, so we need to think about incorporating boosters into the model,” Wagner said. “It’s possible that everyone may need boosters, […] but if we allow evolution to happen by not vaccinating the rest of the world, then we don’t know how long the gains from a booster would be beneficial for anyways. While vaccine supplies and availability are limited, it’s a zero-sum game [as] vaccinating here means not vaccinating somewhere else.”

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