Research suggests physical distancing rules are based on ‘outdated science’

‘Current rules on safe physical distancing are based on outdated science.’
 
That is the argument of the authors of a new analysis, published in The BMJ on 25 August.
 
They say the notion of maintaining a physical distance of 1–2 m in order to reduce transmission risk of SARS-CoV-2 overlooks the physics of respiratory emissions, and does not take into account important factors such as the emitter’s viral load, duration of exposure, ventilation, and an individual’s susceptibility to infection.
 
The analysis also says evidence suggests SARS-CoV-2 may travel more than 2 m through activities such as coughing and shouting.
 
The authors explain the 1–2 m distancing rule originated in the 19th century. However, they say eight of 10 studies in a recent systematic review showed horizontal projection of respiratory droplets beyond 2 m for particles up to 60 μm.
 
‘In one study, droplet spread was detected over 6–8 m,’ the authors wrote.
 
‘These results suggest that SARS-CoV-2 could spread beyond 1–2 m in a concentrated packet through coughs or sneezes.
 
‘In recent related viral outbreaks, such as SARS-CoV-1, MERS-CoV, and Avian flu, multiple studies reported suspected spread beyond 2 m.’
 
Associate Professor Hassan Vally is an epidemiologist with a special interest in infectious diseases at La Trobe University. He told newsGP that transmission of SARS-CoV-2 at distances beyond 1–2 m is possible, but unlikely to be a major route of transmission.
 
Associate Professor Vally believes the authors of the new analysis may potentially be ‘overweighting’ the likelihood of being infected at longer distances.
 
‘Whilst we have theoretical models that say it is possible for those droplets to travel that far, that does not mean that this occurs often. And as the authors indicate, there are a whole range of other variables that play a role in whether someone gets infected,’ he said.
 
Associate Professor Vally says the idea that transmission of SARS-CoV-2 does not commonly occur at great distances is evidenced by the reproductive number.
 
‘If it was happening a lot, you would perhaps expect the reproductive number would be higher,’ he said.

Associate Professor Vally is not disputing the fact some research has shown the ability for viruses such as SARS-CoV-2 to travel distances greater than 1–2 m.
 
‘It’s not just whether this is possible, it’s whether this is a common enough route of transmission to justify changing recommendations based on it,’ he said.
 
‘If you just look at what we do know from the real world, we don’t have that many reports that can actually prove that a person was infected at that longer distance.’
 
However, the authors of the analysis believe that based on the possibility of SARS-CoV-2 transmission from greater distances than 1–2 m, recommendations regarding physical distancing rules should be changed.
 
‘Instead of single, fixed physical distance rules, we propose graded recommendations that better reflect the multiple factors that combine to determine risk,’ the authors wrote.
 
‘This would provide greater protection in the highest risk settings but also greater freedom in lower risk settings, potentially enabling a return towards normality in some aspects of social and economic life.’


Associate Professor Hassan Vally says current evidence suggests most transmission of SARS-CoV-2 occurs at distances less than 2 m.
 
The authors say that in the highest risk situations – which they define as indoor environments with poor ventilation, high levels of occupancy, prolonged contact time, and no face coverings (such as a crowded bar or night club) – physical distancing beyond 2 m and minimising occupancy time should be considered.
 
Likewise, the authors say less stringent distancing is likely to be adequate in low-risk scenarios.
 
The authors note physical distancing should be seen as ‘only one part’ of a wider public health approach to contain spread of COVID-19.
 
‘It needs to be implemented alongside combined strategies of people-air-surface-space management, including hand hygiene, cleaning, occupancy and indoor space and air managements, and appropriate protective equipment, such as masks, for the setting,’ the authors wrote.
 
Associate Professor Vally is concerned about the authors’ advice to consider changing the current, easy-to-understand public health recommendations regarding physical distancing into a graded system.
 
‘The risk is that this confuses and undermine the public health messaging,’ he said.
 
He says current messaging is based on reducing the probability of infection, not eliminating it completely.
 
Associate Professor Vally says there have been some ‘superspreading’ events reported, such as in choirs.
 
‘But we’ve had millions of infections and we’re not seeing a large number of reports of people who are clearly being infected at long distances from other people,’ he said.
 
He likens this scenario to the recent case report of a person who was reinfected with SARS-CoV-2.
 
‘It’s a similar situation,’ he said. ‘We’ve had millions and millions of people who’ve been infected and you’ve got one case report that looks pretty solid and clear that they’ve been reinfected, but you’re always going to see these unusual events, and you shouldn’t overreact to them.’
 
Rather than changing public health messages based on a very small probability of infection at greater distances, Associate Professor Vally believes it is best to adhere to current recommendations on physical distancing, along with other practices that can reduce infection risk.  
 
‘The only reason we have a 1 m or 1.5 m cut-off is because we’re saying your likelihood of being infected beyond that distance is so small,’ he said.
 
‘And it’s a simple message.’
 
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