WHO's expert vaccine advisers on Wednesday recommended Johnson & Johnson's Covid-19 jab for use in countries where coronavirus variants of concern are circulating.The World Health Organization gave its seal of approval on Friday to the vaccine, which has the advantages of being a single-shot jab that can be stored at regular refrigeration rather than ultra-cold temperatures.After meeting on Monday, the WHO's Strategic Advisory Group of Experts (SAGE) on Immunization issued its recommendations Wednesday on how the vaccine should be used -- and said it had proven effective against what are termed variants of concern.Comparing mass trials of the vaccine in different countries, SAGE said that despite the South African variant being predominant.