In the most extreme scenario — with wealthy nations fully vaccinated by the middle of this year, and poor countries largely shut out — the study concludes that the global economy would suffer losses exceeding $9 trillion, a sum greater than the annual output of Japan and Germany combined.

Nearly half of those costs would be absorbed by wealthy countries like the United States, Canada and Britain.

In the scenario that researchers term most likely, in which developing countries vaccinate half their populations by the end of the year, the world economy would still absorb a blow of between $1.8 trillion and $3.8 trillion. More than half of the pain would be concentrated in wealthy countries.