Money is not the main issue. Each additional dose is likely to cost $5 to $7. (The Biden administration is paying roughly $7 per dose for the Pfizer shots it is donating.) In all, a campaign to vaccinate the rest of the world — at a cost of $50 billion to $70 billion — would amount to less than 0.1 percent of global economic output this year. “The costs of being in this pandemic are so enormous,” Rachel Silverman of the Center for Global Development told us. “It will be history’s greatest bargain if for $50 to $70 billion we can vaccinate the world and get out of this crisis.” The cost is low enough that poorer countries can afford to cover much of it on their own. But it represents such a tiny share of rich countries’ budgets that many experts have called on the G7 to take the lead. The International Monetary Fund has suggested using grants from rich countries, nongovernmental agencies and charities.