evidence: More than one million cases of COVID-19 have been confirmed as of 2 April, according to data compiled by researchers at Johns Hopkins University in Baltimore, Maryland. But in much of the world, people exhibiting mild or no symptoms are unable to get tested, meaning that the true number of cases could be much higher. [...] The COVID-19 pandemic could have infected 90% of the world’s population and killed 40.6 million people if no mitigation measures had been put in place to combat it, according to estimates from an influential modelling group at Imperial College London. The report from the Imperial College COVID-19 Response Team, published on 26 March, highlights the importance of acting early to suppress the outbreak. The analysis says that introducing social distancing, testing and isolation of infected people would cut worldwide deaths to 1.9 million, if carried out when each country’s fatality rate was 0.2 deaths per 100,000 people per week. Implementing these measures only when the death rate reaches 1.6 per 100,000 people per week would lead to 10.5 million lives lost globally, it finds. According to Nature’s analysis of death rates from Our World in Data — counting each day at the centre of a rolling weekly window of deaths — Italy hit the 0.2 threshold on 2–3 March, the United Kingdom on 17 March and the United States on 22 March.