Researchers at King’s College London say the loss of sense of smell and taste could be the best way to tell if you have Covid-19, after tracking symptoms via their specially-created app. By the end of March, the app had more than 1.8 million users sign up to log their symptoms. Some 59% of the 1.5 million people who had tested positive reported a loss of smell and taste, compared with 18% of those who tested negative, analysis of the data showed.