PEYTON FLEMING DOZENS of children at a clinic in North Kivu, on the eastern border of the Democratic Republic of Congo (DRC), received a measles vaccine in May, made possible by a quiet revolution in refrigeration that keeps vaccines cold, even in places without reliable electric power. The "solar direct-drive" refrigerators – plain, box-like coolers that do not require fuel or batteries - have helped boost child vaccinations in DRC's poorest rural provinces by 50% in the past year, according to global vaccine alliance Gavi. That has helped cut child mortality in DRC to half of what it was two…