Two years into the pandemic, most of us are fed up. COVID case rates are higher than ever and hospitalization rates are again increasing rapidly in many countries.

Faced with this bleak picture, we yearn for a return to normalcy. We would like to meet friends in a pub or take them out to dinner. We want our ailing business to thrive like it did before the pandemic. We want our children to return to their once-familiar routine of in-person instruction and extracurricular activities. We’d love to ride the bus, sing in a choir, go back to the gym, or dance at a nightclub without fear of catching COVID.

Which of these activities is safe? And how safe exactly? These were the questions we tried to answer in our latest study.

SARS-CoV-2, the virus that causes COVID, spreads primarily through airborne transmission. So the key to preventing transmission is to understand how airborne particles behave, which requires knowledge of physics and chemistry.

Air is a liquid made up of invisible, rapidly and randomly moving molecules, so airborne particles disperse indoors over time, e.g. B. in a room or on a bus. An infected person can exhale particles containing the virus, and the closer you are to them, the more likely you are to inhale some virus-containing particles. But the longer you two stay in the room, the more the virus spreads. When you’re outdoors, the space is almost infinite, so the virus doesn’t build up in the same way. However, someone can still transmit the virus if you are close to them.

Viral particles can be released whenever an infected person breathes, but especially when their breathing is deep (such as when exercising) or associated with vocalizations (such as speaking or singing). While wearing a well-fitting mask reduces transmission because the mask blocks the release of viruses, the unmasked infected person sitting quietly in a corner is much less likely to infect you than one who approaches you and one heated argument begins.

All variants of SARS-CoV-2 are equally airborne, but the likelihood of contracting COVID depends on the transmissibility (or contagiousness) of the variant (Delta was more contagious than previous variants, but Omicron is even more contagious) and how many people are currently infected (prevalence of the disease). At the time of writing, more than 97% of COVID infections in the UK are Omicron and one in 15 people is currently infected (6.7% prevalence). Although Omicron appears to be more easily transmitted, it also appears to cause less severe disease, particularly in vaccinated individuals.

likelihood of becoming infected

In our study, we quantified how the various influencers on transmission alter your risk of developing the disease: viral factors (transmissibility/prevalence), human factors (masked/unmasked, exercise/sedentary, loud/quiet), and air quality factors (indoor/outdoor, large space/small space, crowded/uncrowded, ventilated/unventilated).

We did this by carefully examining empirical data on how many people became infected during superspreader events, where key parameters such as room size, room occupancy and ventilation levels were well documented, and using a mathematical model to represent how transmission occurs.

The new chart, adapted from our paper and shown below, gives a percentage chance of being infected in different situations (you can enlarge it by clicking on it).

A surefire way to catch COVID is to do a combination of things that get you in the dark red cells on the chart. For example:

  • Gather with many people in an enclosed space with poor air quality, such as a B. a poorly ventilated gym, nightclub or classroom

  • Do something strenuous or rough like exercising, singing, or shouting

  • Leave your masks off

  • Stay there long.

To avoid contracting COVID, try to stay in the green or yellow squares of the table. For example:

  • If you must meet with other people, do so outdoors or in a well-ventilated place, or meet in a place where ventilation is good and air quality is known

  • Keep the number of people to a minimum

  • Spend as little time together as possible

  • Don’t shout, sing, or do heavy exercises

  • Wear high-quality, well-fitting masks from the time you enter the building until you leave it.

While the chart gives an estimated number for each situation, the actual risk depends on the specific parameters, e.g. B. how many people are exactly in a room with what size. If you want to enter your own data for a specific environment and activity, you can try our COVID-19 Aerosol Transmission Estimator.

Trish Greenhalgh, Professor of Health Sciences in Primary Care, University of Oxford; Jose-Luis Jimenez, Distinguished Professor, Chemistry, University of Colorado Boulder; Shelly Miller, Professor of Mechanical Engineering, University of Colorado Boulder, and Zhe Peng, Research Scientist, University of Colorado Boulder

This article was republished by The Conversation under a Creative Commons license. Read the original article.


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