"an epidemic's growth is mostly driven by a minority of highly interactive individuals, and that reducing the interactions of these is key to getting an epidemic under control."
A new study (https://doi.org/10.1101/2020.04.11.20062042) from Professor Christopher Ramsey, a physicist who specialises in probability-based modelling in the School of Archaeology, is focussed on the effectiveness of social distancing in controlling epidemics.
The report argues that it is essential to consider the very wide variation in the amount of interaction individuals have with others in developing strategies. It uses a very simple theoretical model to illustrate how an epidemic's growth is mostly driven by a minority of highly interactive individuals, and that reducing the interactions of these is key to getting an epidemic under control. These people may have jobs that require high-interaction levels, be highly interactive out of choice, or live in conditions where they are in close contact with many others.
The analysis suggests that were we able to cap the amount of interaction any individual had at a level similar to that for the average person, that this on its own would be enough to reduce the epidemic while leaving many people working normally, and that technically a lockdown as should not be necessary. However, Prof Ramsey concedes that, in practice, a lockdown may be the only way to reduce contacts for the very interactive minority.
The report looks at a number of different possible scenarios. One of these considers why you might fail to control an epidemic, with the majority of the population in lockdown, and key worker with normal interaction levels. In this situation the epidemic essentially takes off independently within the group of key workers. This underlines the importance of social distancing and other measures, such a protection and testing, to control the epidemic within that group.
Prof Ramsey is optimistic about the ability for sustainable social distancing to control epidemics, but only in concert with other methods such as contact tracing and testing. He recommends that we should consider the notion of people trying to cap interactions with others at some reasoable level, prioritising those interactions that are most important to us. Mobile phone apps might be useful in helping us to monitor our close exposure to others, especially in urban environments, so that we can try to keep this under control. Until there is a vaccine, we might have to consider interaction time like exposure to the sun, very beneficial in limited amounts - but harmful in excess.