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11 November 2020

To defeat Covid-19 the UK needs to remember the three Cs

Japan presciently identified closed spaces, crowded places and conversations as breeding grounds for the virus. 

By Stuart Ritchie

“Face, Space, Place.” Wait – what is it, again? Ah yes: “Hands, Face, Space.” The UK government’s coronavirus slogan emphasises the need for handwashing, facemasks and staying two metres apart. It covers the three types of transmission of a respiratory disease such as Covid-19: by “fomites” (that is, contaminated objects or surfaces that might be touched), by exhaled droplets from an infected person, and by tiny particles that might linger in the air.

But by putting those three words in that order – hands, then face, then space – has the government got it backwards? Despite the UK’s zealous promotion of handwashing from the start of the outbreak (“Sing Happy Birthday twice” and all that), scientific discussions in the past weeks and months have begun to converge on the idea that we might have paid too much attention to fomites – the “hands” part – and too little to those airborne particles.

Compare the health advice from another government, that of Japan. As early as 29 March, the Japanese prime minister’s office tweeted a poster that described the “three Cs” you should avoid to keep your Covid-19 risk low. They are: closed spaces with poor ventilation; crowded places with many people; and close-contact settings such as conversations. There was also a minor note at the bottom about disinfecting surfaces. The poster showed a Venn diagram emphasising that it’s the overlap of the three Cs that individuals should most avoid: when all three are present, the risk of infection is particularly high. 

That early advice turns out to have been remarkably prescient. It was based on Japanese analysis of a fourth C: clusters. Japanese researchers energetically investigated the initial Covid-19 cases that arrived from China. As well as tracing infections forwards – contacting all the people who met someone with a confirmed infection and checking their symptoms – the Japanese researchers also focused on backwards tracing – working out where a person had been and identifying aspects of their environment that might have helped spread the virus. 

This kind of analysis was what suggested the importance of the three Cs, and it pointed to something else, too: a small minority of cases, the so-called super-spreaders, are responsible for the majority of infections. Economics fans might be reminded of the Pareto principle, named for the fin de siècle economist Vilfredo Pareto, who noted that 20 per cent of the people in Italy owned 80 per cent of the land (this also occurs in many other places). For Covid-19 it’s more like 10 per cent of cases causing 80 per cent of new infections, but the minority-infects-majority principle – a phenomenon known in epidemiology as “overdispersion”, and which results in a noticeable clustering of infections – remains the same.

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[See also: Samuel Horti on the failures of the government’s Covid-19 slogan]

Subsequent research bears out the super-spreader idea. More recent studies support other aspects of the three Cs: for example, evidence is mounting about the importance of airborne transmission; some scientists argue that fomite transmission is relatively rare; and others have emphasised the need to think seriously about the ventilation of rooms and to provide fresh air to dilute the potentially infectious airborne particles. Indeed, the World Health Organisation recently updated its coronavirus advice page to include the three Cs.

So why hasn’t the UK government added three Cs-like advice to its slogans? Perhaps it’s because the government doesn’t want to overload people with yet more advice and guidelines. Or maybe it’s because, paradoxically, their standards are too high: they’re waiting for the definitive study of Covid-19 transmission that irons out the still-contentious fomite/droplet/airborne debate. But such a study might never arrive (and in any case, different types of transmission could be important in different contexts). Instead of making the perfect the enemy of the good, we should use the reliable evidence we have available.

Several signs point to the UK beginning to follow Japan’s lead on this question, even after a six-month lag. A new Sage subgroup document, written on 30 September and made public on 23 October, offers advice on improving ventilation and recommends discussing it in public health campaigns. And England’s deputy chief medical officer, Jonathan Van-Tam, explicitly referenced the three Cs in a mid-October press conference.

It’s time for an update. Once the UK exits the current lockdown, “Hands, Face, Space” should either be inverted to emphasise the “space” part, or dropped entirely. It should be replaced with a slogan that still points to handwashing and mask-wearing, but also highlights the three Cs.

And it won’t be a moment too soon: although government advice needs to be internally consistent, it can’t remain consistent over time. As ever-more studies emerge, scientists are revising their knowledge about Covid-19 transmission. We need to make sure that knowledge – rather than the virus – is transmitted to the public.

[See also: Phil Whitaker on how scientists are grappling with understanding the complexity of Covid-19]

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