Clinical trials in Brazil of a Chinese-made vaccine against Covid-19 have shown “extremely positive” results, and a widespread vaccination campaign could begin as early as December, the governor of Sao Paulo state said on Wednesday.Sao Paulo, the epicentre of the coronavirus pandemic in hard-hit Brazil, is one of six states helping to test the so-called CoronaVac vaccine developed by Chinese pharmaceutical firm Sinovac Biotech.The vaccine produced an immune response in 98 per cent of recipients…