The evidence regarding indoor work spaces and Covid transmission is clear, and it’s not what the government is saying, argues Alistair Cartwright

Boris Johnson’s speech to the nation on Sunday 10 May scattered the seeds of confusion far and wide. Above all though, the relaxation of the lockdown is about getting people back to work: back to making money for businesses. People who can’t work from home will be ‘actively encouraged’ to return to their workplaces – despite a death rate that only two days before Johnson’s speech hit 626. But don’t worry, the government will offer guidelines on making workplaces ‘covid-secure’.

Those guidelines have now been published. They include things like working ‘back-to-back’ or ‘side-to-side’ (rather than face-to-face), using screens and barriers, establishing one-way flows at entry and exit points, increasing handwashing facilities, and staggering arrival and departure times. Worryingly, all of these measures are framed by the ubiquitous qualifier ‘wherever possible’. Employers should rearrange workstations ‘wherever possible’. Maximum lift capacity should be reduced ‘wherever possible’. Even a token gesture like providing extra bike racks: ‘where possible’. 

It’s difficult to see how this series of optional adjustments could add up to a ‘covid-secure’ workplace. But even if the guidelines were implemented, they show a dangerous lack of understanding about how the virus spreads in enclosed spaces.

As Erin Bromage, Associate Professor of Biology at the University of Massachusetts, writes: ‘Social distancing guidelines don’t hold in indoor spaces where you spend a lot of time’. The two-metre rule can protect you from ‘brief exposures’, in a shop for example, or ‘outdoor exposures’, because in these situations ‘there is not enough time to achieve the infectious viral load’. Other factors such as wind flow together with ‘infinite outdoor space for viral dilution’ effectively reduce the viral load.

Inside an enclosed space the mechanics of how the virus spreads through the air are different. Bromage points to two recent studies of outbreaks that researchers traced back to specific places, one a restaurant in Guangzhou, the other a call centre in Seoul.

Take the Guangzhou restaurant case, illustrated in the diagram below, and in this analysis from Bromage:

‘The infected person (A1) sat at a table and had dinner with 9 friends. Dinner took about 1 to 1.5 hours. During this meal, the asymptomatic carrier released low-levels of virus into the air from their breathing. Airflow (from the restaurant’s various airflow vents) was from right to left. Approximately 50% of the people at the infected person’s table became sick over the next 7 days. 75% of the people on the adjacent downwind table became infected. And even 2 of the 7 people on the upwind table were infected (believed to happen by turbulent airflow). No one at tables E or F became infected, they were out of the main airflow from the air conditioner on the right to the exhaust fan on the left of the room.’

Let’s state those results again. After 1.5 hours, three quarters of people sitting at the next table were infected. A 3 or 4 metre gap failed to protect nearby diners. Airflow was a decisive factor.

The outbreak at the Seoul call centre is in many ways even more revealing. Here’s Bromage again, giving a synopsis of the South Korean study:

‘A single infected employee came to work on the 11th floor of a building. That floor had 216 employees. Over the period of a week, 94 of those people became infected (43.5%: the blue chairs). 92 of those 94 people became sick (only 2 remained asymptomatic). Notice how one side of the office is primarily infected, while there are very few people infected on the other side… Another 3 people on other floors of the building were infected, but the authors were not able to trace the infection to the primary cluster on the 11th floor. Interestingly, even though there were considerable interactions between workers on different floors of the building in elevators and the lobby, the outbreak was mostly limited to a single floor.’

The number of cases due to surface transmission aren’t known in this example, but the fact that cases were almost entirely confined to one floor suggests the decisive nature of respiratory exposure. The study highlights how sharing the same air for a prolonged period increases the chance of infection. A single person spread the infection to over 40% of colleagues on their floor during the course of a week. If we focus on the side of the room where the outbreak was concentrated, the infection rate was more like 55%.

Covid-19 is a deadly virus that spreads in the air. In enclosed spaces the infection rate is very high indeed, regardless of social distancing measures. It’s no surprise then that the biggest known outbreaks have happened in prisons, places of worship and workplaces.

This much we already knew. But what these detailed studies demonstrate plainly is that ‘common sense’ measures like handwashing and social distancing are simply not enough in most workplace environments. The UK government guidelines on ‘covid-secure’ workplaces are not only pathetic, they are dangerously deceptive about how the virus actually works. Hand sanitizer, 2-metre gaps marked out with hazard tape, one-way entrances and the like will probably only make a very small difference in reducing the risk of infection. Other measures like working back-to-back or side-to-side are frankly laughable. Plastic screens may or may not help, depending on airflow. Measures that might plausibly help, such as improving ventilation, are barely mentioned. Other sensible measures like temperature-monitoring surveillance are absent from the guidelines. In truth, there is no such thing as a ‘Covid-secure workplace’.

So, what would reduce the risk? We’ve known the answer all along. Maintain lockdown long enough to drive down case numbers and the reproduction rate to the kind of figures seen in places like South Korea, China, Cuba, or New Zealand, and make sure you have mass testing and tracing in place, with the capacity to quickly pounce on any localised outbreak.

These were precisely the conclusions drawn by the South Korean team that meticulously tracked down the infections in that Seoul call centre:

‘By testing all potentially exposed persons and their contacts to facilitate the isolation of symptomatic and asymptomatic COVID-19 case-patients, we might have helped interrupt transmission chains.’