New study reveals where (and how) you are most likely to catch Covid

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

Faced with this bleak picture, we yearn for a return to normality. 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? We tried to answer these questions in our latest research.

SARS-CoV-2, the virus that causes COVID, mainly spreads through air transmission. So the key to preventing transmission is understanding how particles behave in the air, 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, 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.

Virus particles can be emitted every time an infected person breathes, but especially when they involve deep breathing (e.g., exercising) or vocalizations (e.g., speaking or singing). While wear a well-fitting mask reduces transmission because the mask blocks the release of the virus, the unmasked infected person sitting quietly in a corner is much less likely to infect you than one who approaches you and starts a heated argument.

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 (the prevalence of the disease). At the time of writing more than 97% of UK COVID infections are omicron and one in 15 people is currently infected (prevalence 6.7%). 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 different 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 chart. 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. on how many people are exactly in a room and what size. If you fancy entering your own data for a specific environment and activity, you can try ours COVID-19 Aerosol Transmission Estimator.

Trish Greenhalgh, Professor of Health Sciences in Primary Care, University of Oxford; Jose Luis Jiménez, Distinguished Professor, Chemistry, University of Colorado Boulder; Shelley Miller, professor of mechanical engineering, University of Colorado Boulder, and Zhe Peng, Research Scientist, University of Colorado Boulder

This article is republished by The conversation under a Creative Commons license. read this original article.

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