Coronavirus: any science behind rule of six?

New coronavirus restrictions in England include a six-person limit on gatherings. What's the reasoning?
22 September 2020

Interview with 

Gabriel Scally, University of Bristol


Families and groups of people sitting on the grass in a park.


This week the number of COVID cases reported worldwide passed 30 million, with recorded deaths approaching a million and counting. We’ve seen surges in the countries worst hit - that’s India, Brazil, and the USA - but also in Argentina, France, Spain, and many others. Israel was the first country to enter a second national lockdown, ahead of the Jewish “high holy days”. Here in the UK there has been a sharp spike in cases, although without a corresponding increase in deaths, likely because this spike is mostly - at the moment - among younger people. In response to this, on Monday the government introduced the “rule of six” limit on gatherings, and Boris Johnson announced an ambitious plan for wide scale mass testing called “Operation Moonshot” - but this has proved to be embarrassing as testing facilities across the country were overwhelmed. What is the scientific rationale behind these interventions, will they even work, and what are the alternatives? Chris Smith asked the University of Bristol’s Gabriel Scally: first of all, why pick 6?

Gabriel - Well, I think it probably comes from that scientific method of wetting a finger and raising it to the wind. There doesn't seem to me to be any science about it. If one was to try and come up with something that had some scientific background, you would look at population density, you would look at household size in particular; and we do know that the places where the virus is at its most prevalent have poor housing and overcrowding, and these tend to be amongst the most deprived areas in the country. So I don't think there is science behind it, but we should be paying attention to household construction, I think that's extremely important: I mean the age and the generations involved in living together in a house.

Chris - They're going for then the domestic setting, because the figures that have been published suggests that's where the bulk of the transmissions occur. Is the rationale then that if you limit the number of people getting together in households, you do cut off the virus transmission at its knees, at least a bit?

Gabriel - I don't know if you can cut something off at its knees a bit! But yes, that would be the idea behind it. Now whether it'll work or not is another question, because the virus pops up in various different places, and we've already seen a significant number of workplace outbreaks, often to do with the food industry and often to do with migrant workers. And often that is difficult to discern whether the transmission is the workplace or the living conditions, in which migrant workers are often grouped together. So the answer I think is not in the area of trying to make some very precise social restrictions. We need a broader, deeper approach to the virus; and that's just not what we're getting.

Chris - You're in reasonable company, because a number of other academics have come out and said that people just won't tolerate this, and this will actually breed some degree of disrespect for the rules rather than respect for the rules. And that will lead to more flouting of the rules and actually more transmissions, especially with Christmas approaching.

Gabriel - I think there's a lot in the behavioural science behind that. And certainly people's confidence in what they're asked to do is really, really important, and community solidarity is extraordinarily important; and if you lose the confidence of the public, well, then you lose the battle against the virus. One of the anachronisms is talking about policing with marshals and fines and so on, and I don't like the idea that we have to spy on each other and report each other to the police. This is not how you mobilise an entire community to deal with this infectious disease.

Chris - The most recent announcements dwell very heavily on testing this whole concept of a 'moonshot': talking about, by October, scaling up testing to four- or five-fold over what we're seeing at the moment, and then possibly into million scale testing by next year. Do you think they've lost confidence in the question of a vaccine, and so now they're going down the test route?

Gabriel - Well, it's a very interesting question because on several occasions there have been interventions from the top, which have sought to cast a really, really optimistic picture before us: herd immunity, the promise of an app, huge enthusiasm from the very top about antibody testing, and that was going to be the next great thing. And now we've got the moonshot. It's no substitute for doing the hard public health graft to get this virus under control and a strategy to back that up.

Chris - So what would that hard public health graft be? What would you do differently than the present strategy, or lack of, that we see playing out?

Gabriel - I would construct a system which had all the elements to it: find, test, trace, isolate, and support. And there are also reports of people not coming forward for testing because they know they'll be told to isolate, and they won't be able to go to work and earn the money they need because they're on a zero hours contract. So therefore I would take the very large sum of money that is being wasted on an ineffective, non-functioning NHS test and trace system and plow it into local areas: building up public health teams, making use of people like health visitors who know their communities, environmental health officers who do contact tracing for infectious disease all the time, and community leaders, particularly from ethnic minority communities, and local councillors as well, to really turn it into a community effort.


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