JENNIFER RIGBY AFRICAN countries are lining up to approve a new vaccine for malaria, with 20 million doses available for them to buy this year, the shot’s manufacturer told Reuters. This week, Nigeria's medicines regulator followed Ghana's, with the two nations becoming the first countries in the world to back the new R21 vaccine, developed by scientists at Oxford University and manufactured by the Serum Institute of India and Novavax. The move was unusual as it came before the World Health Organization's approval. African countries that do not have extensive resources for drug regulation have previously relied on the U.N. agency to initially review…