The World Health Organisation said on Friday that it did not expect widespread immunisation against the novel coronavirus until mid-2021, despite growing expectations in the US and beyond that a vaccine could be released within weeks.Across the world, governments are hoping to announce a vaccine as soon as possible and roll out treatments for Covid-19, which has killed nearly 870,000 people and infected well over 26 million.The UN health agency welcomed the fact that a “considerable number” of…