ALEXANDER WINNING  EFFICACY results may not be ready for months from a trial of AstraZeneca and Oxford University's coronavirus vaccine in South Africa, the principal investigator of the South African study told Reuters. AstraZeneca published findings this week from trials in Brazil and Britain showing its vaccine was on average about 70% effective in preventing coronavirus infection. It is seeking regulatory approval in several countries for its shot. However, the company has faced calls to provide more data, after it found that the efficacy was higher in a small sub-group of participants given a smaller initial dose. A larger U.S.…