With the earliest cases of COVID-19 in the UK, it was possible to perform contact tracing and shut down early chains of transmission. The data suggests that there wasn’t a single case that began the virus’ spread across the UK, but multiple cases, each with their own transmission chains.

It’s likely that cases arrived relatively early London due to its centrality in the nation and as much of the country’s transport infrastructure is built around getting people in and out of London. With many international imports of new cases, eventually the approach of contact tracing is overwhelmed and transmission takes hold within the UK, requiring the introduction of more severe overall social distancing measures to control transmission.

Once cases are rising exponentially, in order to contain the pandemic we must reduce the number of people that each contagious person infects. In disease dynamics, this reproduction ratio is called R. For any epidemic or pandemic to die out, in the absence of a vaccine, the effective R needs to be less than one: that is, if each contagious person infects less than one other person, then the number of new cases will slow and, eventually, stop. Current data suggests that the original reproduction ratio, R0, for coronavirus was between 1.5 and 3.5.

For modellers like Gog, Professor of Mathematical Biology in DAMTP, knowing how and when people come into contact with other people helps determine R, and in turn helps develop a model of how a pandemic spreads.

The BBC Pandemic project provides a highly useful source of data on how we most often come into contact with others. For those of working age, the workplace is the source of much person-to-person contact, so switching to remote working for those who can do so will reduce transmission between workplace colleagues. For those over 65, who are most at risk from severe illness due to COVID-19, most contact occurs outside the home, in places such as shops, restaurants and leisure activities, so shutting down these non-essential activities is also key to reducing R.

Earlier in the pandemic, there was criticism of the Government’s initial reluctance to close schools. However, Gog says that all the evidence suggests that school closures will only reduce transmission rates between 10 and 20 percent. Earlier models of the spread of seasonal ‘flu have looked at schoolchildren as key spreaders, but the behaviour of children, in particular teenagers, has changed a great deal in the past decade: teenagers now do much of their socialising online, and don’t so often gather in large groups as much as older generations did, a point that was confirmed by the BBC Pandemic data. In addition, it is unclear at the moment how much role children play in coronavirus transmission, whether they are as susceptible and infectious as adults.