Analysis: We have entered a dangerous new phase of the pandemic

Professor Andrew Hayward (UCL Epidemiology & Health) explains why the new, more infectious, strain of Covid-19 is a cause for concern and suggests what must be done to reduce transmission of the disease. On the last day of 2019 the World Health Organization (WHO) received the first reports of an unusual cluster of pneumonia cases in Wuhan, China. Since then the causative agent, SARS-CoV-2 has gone on to kill more than 1.8 million people worldwide. As 2020 drew to a close, a new strain of Covid-19 was reported to WHO by the chief medical officer of England. The high replication rate of viruses provides myriad opportunities for mutations. The vast majority of these provide no selective advantage, leading the mutated strain to die out or remain at low levels. The UK has invested in the world's largest SARS-CoV-2 sequencing programme, routinely sequencing around 5-10% of all samples nationally.