Can we vaccinate the world?

Since pandemics do not stop at national borders, richer countries might benefit from helping poorer countries fight them.

Donating surplus vaccines to vaccine-poor countries combating a new variant can actually be in our own self-interest.

Why?

Because quick and large-scale rich-to-poor world vaccine donation might slow or halt the progression of the new variant inside the vaccine-poor world and thus prevent the new variant from reaching the vaccine-rich world’s borders and doing large new damage there.

When will this be the case?

In a study just out at Communications Medicine (Nature Research), I worked together with a multidisciplinary team of researchers from Germany and Israel to develop a ‘Rich-to-Poor Vaccine Donation Game’ to answer this question of key importance for global health.

There are two primary challenges in deciding how to distribute vaccines from rich to poor countries: how many vaccines is it ideal for the rich countries to give and under what circumstances will the rich countries actually cooperate to make such optimal levels of donation really happen in practice.

Below I will elaborate on how we modeled this strategic decision problem and share our findings on whether and when we can expect rich-to-poor vaccine donation to happen.

When will rich-to-poor vaccine donation happen?

Policy-wise, the question is complex. The benefits to vaccine-rich countries of giving away their surplus stock (after full vaccination of their own population) depend on many factors at once.

These include, crucially, the share of the vaccine-poor world which the vaccine-rich countries could actually cover, but also the likely emergence of new variants of concern and the unavoidable cost of a new virus outbreak even when stocking rather than donating all surplus vaccines.

Politically, the question is strategic: since no country can cover the entire vaccine-poor world on its own, the vaccine-rich countries need to work together.

Yet it is safe to assume that national self-interest will dominate the thinking of political decisionmakers, much like vaccine nationalism is likely to loom large in the thinking of their voters.

So we need to address two questions. First, the optimality issue. Which surplus vaccine donation strategy – none, partial, or full - is the single best course of action for the vaccine-rich countries as a whole?

Second, the stability issue. Will each vaccine-rich country actually adopt this optimal strategy willingly and stick to it, rather than opting out or freeriding on the efforts of other vaccine-rich countries?

Four important insights

To address these complex issues, our team developed a game-theoretic model, the ‘Rich-to-Poor Vaccine Donation Game’.

The model analyzes the strategies of rational decision making by the vaccine-rich countries, how they depend on strategies of other rich countries.

It also takes into account parameters such as the fraction of the global unvaccinated population potentially covered, the expected emergence rate of variants of concern, and the unavoidable cost of a new virus outbreak even when all surplus doses are in stock.

To determine whether the optimal strategy for vaccine-rich countries is actually stable, we explored two different equilibrium concepts, Nash equilibrium or self-enforcing agreement.

Our results provide at least four sources of unexpected new insights.

The best argument to donate? Self-interest

1. Doing the same thing jointly is important. The vaccine-rich countries have to adopt the same donation strategy: there are no scenarios in which different countries doing different things is the best course of action.
2. Given the strategic nature of donating one’s own vaccines to produce a public good (global health), the optimal donation strategy will more often be likely to stick when there are fewer rather than more vaccine-rich countries.
   This is because vaccine-rich countries will then find it much easier to monitor each other’s actual contributions and to keep the joint agreement working.
3. But importantly, if vaccine-rich countries can jointly vaccinate a very large share of the vaccine-poor world, it is actually the best course of action from their own viewpoint to donate all of their surplus vaccines, irrespective of how likely it is that new variants of the virus will occur later.
   Because the more vaccinated people there are globally, the less risk there is of new variants emerging.
   And in most cases, this optimal full-donation strategy will also be stable in the real world. In other words, if production of vaccines can be on a large enough scale - a technical question, not a political one – then there are good grounds for actually achieving full world coverage.
4. Lastly, even in a more realistic scenario in which vaccine-rich countries cannot reach this very high level of poor-world coverage, donating some of their surplus vaccines is still their best course of action in a specific set of circumstances, notably a low likelihood of new variants.
   But this optimal partial-donation solution is less often stable, because each individual vaccine-rich country now has much stronger incentives than before to opt out or never enter such a partial-donation coalition.

The policy lesson: a narrow corridor of self-interested donation

These results offer hard foundation for modest hope about win-win global pandemic cooperation.

Notably our high-coverage scenario indicates good grounds for expecting global vaccination to be a reachable goal, especially if relatively small coalitions of vaccine-rich countries can technically achieve a large vaccine production capacity.

As we have shown, if vaccine-rich countries can jointly vaccinate a very substantial part of the vaccine-poor world, it is not just optimal for them to donate all of their surplus vaccines, irrespective of the likelihood of new variants of the virus - they will also willingly adopt this strategy, and stick to it.

More generally, our research shows that a narrow corridor of conditions exists under which strict self-interest alone, without recourse to other motivations such as ‘international solidarity’ or ‘vaccine diplomacy’, will make vaccine-rich countries help the vaccine-poor world in fighting global pandemics.

It is on this narrow corridor that international organizations such as the World Health Organization could more fruitfully focus their coordination and cooperation promotion efforts.

This article was originally published on our Danish sistersite, Forskerzonen.

List of references:

• Pieter Vanhuysse's profile (University of Southern Denmark)
• 'A game theoretic approach identifies conditions that foster vaccine-rich to vaccine-poor country donation of surplus vaccines', Communications Medicine (2022), DOI: 10.1038/s43856-022-00173-w