FROM today coronavirus restrictions are being eased in Scotland to allow more people to connect outdoors. Up to four adults from two households will be able to meet, including in private gardens. Non-contact sport can start again for up to 15 people. Along with more children in the classroom and nursing home visits restarting, these changes represent small but important steps forward in emerging from lockdown.

This week also saw headlines about some very different outdoor gatherings involving football supporters. These were not only illegal at the current time, but also criticised because of the infection risk to those gathering and to the police who had to intervene.

So what are the risks of infection outside?

The first thing to make clear is that viruses don’t generally evolve to spread in houses or other buildings. Instead they survive by passing between hosts in nature, which in evolutionary terms has mostly meant outside. That includes respiratory viruses that are passed on when humans or animals breathe, sneeze, cough, call out (including shouting and singing) or come into close contact.

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The virus that causes Covid-19 can be passed on outdoors. But we know from flu and other respiratory viruses that indoor environments are much more risky. This is because they can be passed on through droplets that we are more likely to come into contact with indoors from someone breathing or speaking close to us, or landing onto surfaces that we might touch. Indoor environments with poor air circulation means viruses stay in the air and can be recycled with poor ventilation, so we breathe them in more easily.

There are examples from studies of Covid-19 transmission in restaurants, during choir practice, in work places, and in food factories. The most high risk area by a long shot is our own homes, where it is clear that sharing bedrooms, bathrooms or other living spaces provides multiple opportunities for infection to spread.

Many months on from the start of the pandemic, researchers have been able to assess the risks of indoors vs outdoors. Late last year a review was published in the Journal of Infectious Diseases, suggest that the odds of indoor transmission are around 20 times higher than outdoors, based on research from Japan that analysed a series of cases and clusters of outbreaks. From all the published studies that the authors identified on Covid-19 from a number of countries, fewer than 10% of coronavirus infections happened outdoors.

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This type of evidence helps inform government guidelines in Scotland and elsewhere when deciding what changes can occur, and in what order, as stay at home restrictions are eased. The bottom line is that having a coffee on a park bench with a friend in the open air is much less risky in terms of Covid-19 transmission that popping into a friend’s house to do the same.

It also contributes to why in Scotland children under 12 have been able to play outside in groups during lockdown, as policy makers have weighed up the risks of them losing out on exercise and social interaction with their peers vs infection risk to them (which is very small from this disease). It explains why the easing of lockdown starts with small groups of adults and teenagers being able to meet outside in larger numbers than before – and why I expect hospitality venues to be able to serve customers outside rather than inside when lockdown eases this year, as was the case in 2020.

But going back to my point about how viruses evolve in nature, this doesn’t mean that we can’t ‘catch’ Covid-19 outdoors. We can, but what determines risk outdoors is how close we are and how long we spend with others. You don’t need to be an expert in infectious diseases to understand that lots of people embracing, shouting or singing in close proximity outdoors means someone who is carrying the virus (which is around one in 335 people in Scotland based on the latest ONS Infection Survey) can pass it onto someone else.

As we look ahead, there are some key measures that will allow larger outdoor gatherings in future. The first is that when people meet up outdoors, distancing still matters. If we are to get back to sporting events with punters in seats, then spacing will be key and will limit how many people can watch a match or attend an outdoor concert. Face coverings will help, particularly in communal areas outdoors, for example queuing to get in, or to access toilets.

A further big question is how much vaccines will reduce transmission. Early findings are positive and may mean that, as in Israel, people who have been vaccinated can access indoor venues that others can’t. Israel is providing ‘green passes’ to people who have received both doses of a Covid-19 vaccine. These are shown on a mobile phone app to provide entry to indoor public venues such as gyms and hotels. This type of certification is controversial and could be a divisive policy that will disadvantage those who don’t take up vaccines or are last in the queue for vaccination, like young adults and children. But it is actively being considered in a number of other countries.

For now, we have spring and summer to look forward to in Scotland. We can’t rely on sunshine, but longer days mean we can do more outdoors. Many of us will be able to reconnect with family and friends while keeping the risk of infection low as vaccines continue to be rolled out.

Linda Bauld is Chair of Public Health at the University of Edinburgh.

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