Professor Alessandro Vespignani of Northeastern University in Boston, who led the research, said: ‘This is not a deterministic list, it’s about probabilities – but those probabilities are growing for everyone.

‘It’s just a matter of who gets lucky and who gets unlucky.

‘Air traffic is the driver.

‘But there are also differences in connections with the affected countries (Guinea, Liberia and Sierra Leone), as well as different numbers of cases in these three countries – so depending on that, the probability numbers change.’