British experts have sounded the alarm over a new Covid variant believed to have emerged in Botswana that is the most mutated version of the virus yet. Only 10 cases of the strain, which could be named 'Nu', have been detected so far. But it has already been spotted in three countries, suggesting the variant is more widespread. It carries 32 mutations, many of which suggest it is highly transmissible and vaccine-resistant, and has more alterations to its spike protein than any other variant. Professor Francois Balloux, a geneticist at University College London, said it likely emerged in a lingering...