United Airlines says more than half its workers who weren’t vaccinated last month have gotten the shots since the airline announced that it will require proof of vaccination. The airline is detailing rules around its requirement that employees get vaccinated against COVID-19 by late September. United officials said Wednesday that employees who win an exemption from vaccination because of medical conditions or religious beliefs will be placed on unpaid leave in early October. Those whose exemption requests are denied, and who still refuse to get the shots, will be fired. United is citing “dire” statistics around the COVID-19 outbreak in the United States in explaining its new policy.