LONDON — Lost among the jubilation of America's vaccine rollout this week is an uncomfortable reality: The world's poorest countries will have to wait months and possibly years to see any doses at all.

The U.S., Canada, Britain and the European Union have pre-ordered enough Covid-19 shots to inoculate their populations several times over, subject to regulatory approvals.

In this critical game of medicine logistics — where supply is small but demand immediate and universal — campaigners and some officials accuse these wealthy nations of snapping up orders and hoarding more than they need.

The People's Vaccine Alliance, a collaboration between several aid groups including Oxfam and Amnesty International, has said that unless drastic measures are taken nearly 70 poor countries will be unable to vaccinate 90 percent of their populations next year.