As shipments of Covid-19 shots ramp up for billions of people left behind last year, and new vaccines make their way to the public, dozens of countries are struggling to turn supplies into inoculations. A dearth of immunization sites in Cameroon, weak communication and Covid denial in the Democratic Republic of Congo and a syringe shortfall in Kenya are among the hurdles complicating rollouts. In Zimbabwe, which initially raced ahead of many peers, complacency and a perception of omicron as less serious slowed the campaign; long vaccine queues have turned into a trickle.