A team led by Gabriela Gomes of the Liverpool School of Tropical Medicine argues that it is wrong to assume that herd immunity will only be achieved when 60 per cent of people have been infected. It is more likely, they argue, that the true figure lies between 10 and 20 per cent. The 60 per cent figure, they say, is based on the idea that we are all equally likely to contract the virus. In reality, there is a wide variation in an individual’s susceptibility to becoming infected. People who are frail or who have greater exposure to the virus – perhaps because they are working in an intensive care unit – are in practice far more likely to contract the disease. As the epidemic progresses the pool of easily-infected individuals dries up and the virus has to search out new victims who are less-easily infected.