Rates are stalling in most low-income countries well short of the W.H.O.’s goal to immunize 70 percent of people in every nation. Some public health experts believe the momentum is gone forever. A worker with the South Sudan Ministry of Health called for people in the Mangateen camp for internally displaced people to get their Covid vaccines in Juba last year.Credit…Lynsey Addario for The New York Times In the middle of last year, the World Health Organization began promoting an ambitious goal, one it said was essential for ending the pandemic: fully vaccinate 70 percent of the population in every country against Covid-19 by June 2022. Now, it is clear that the world will fall far short of that target by the deadline. And there is a growing sense of resignation among public health experts that high Covid vaccination coverage may never be achieved in most lower-income countries, as […]