Catching COVID

Here’s where (and how) you are most likely to catch COVID – new study

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Trish Greenhalgh, University of Oxford; Jose-Luis Jimenez, University of Colorado Boulder; Shelly Miller, University of Colorado Boulder, and Zhe Peng, University of Colorado Boulder

Two years into the pandemic, most of us are fed up. COVID case rates are higher than they’ve ever been and hospitalisation rates are once again rising rapidly in many countries.

Against this bleak picture, we yearn to get back to normal. We’d like to meet friends in a pub or have them over for dinner. We’d like our struggling business to thrive like it did before the pandemic. We’d like our children to return to their once-familiar routine of in-person schooling and after-school activities. We’d like to ride on a bus, sing in a choir, get back to the gym, or dance in a nightclub without fear of catching COVID.

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

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

Air is a fluid made up of invisible, rapidly and randomly moving molecules, so airborne particles disperse over time indoors, such as in a room or on a bus. An infected person may 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 the period you both spend in the room, the more spread out the virus will become. If you are 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’re close to them.

Viral particles can be emitted every time an infected person breathes, but especially if their breathing is deep (such as when exercising) or involves vocalisation (such as speaking or singing). While wearing a well-fitting mask reduces transmission because the mask blocks the release of virus, the unmasked infected person who sits 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 chance of catching COVID depends on the transmissibility (or contagiousness) of the variant (delta was more contagious than previous variants, but omicron is more contagious still) and on how many people are currently infected (the prevalence of the disease). At the time of writing, more than 97% of COVID infections in the UK are omicron and one person in 15 is currently infected (prevalence 6.7%). While omicron appears more transmissible, it also seems to produce less severe illness, especially in vaccinated people.

Likelihood of becoming infected

In our study, we have quantified how the different influences on transmission change your risk of getting sick: viral factors (transmissibility/prevalence), people factors (masked/unmasked, exercising/sitting, vocalising/quiet) and air-quality factors (indoors/outdoors, big room/small room, crowded/uncrowded, ventilated/unventilated).

We did this by carefully studying empirical data on how many people became infected in superspreader events where key parameters, such as the room size, room occupancy and ventilation levels, were well-documented and by representing how transmission happens with a mathematical model.

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

Table showing the risk of catching COVID based on various factors.
Risk of catching COVID.
Author provided

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

  • Gather together with lots of people in an enclosed space with poor air quality, such as an under-ventilated gym, nightclub or school classroom
  • Do something strenuous or rowdy such as exercising, singing or shouting
  • Leave off your masks
  • Stay there for a long time.

To avoid catching COVID, try keeping in the green or amber spaces in the table. For example:

  • If you must meet other people, do so outdoors or in a space that’s well-ventilated or meet in a space where the ventilation is good and air quality is known
  • Keep the number of people to a minimum
  • Spend the minimum possible amount of time together
  • Don’t shout, sing or do heavy exercise
  • Wear high-quality, well-fitting masks from the time you enter the building to the time you leave.

While the chart gives an estimated figure for each situation, the actual risk will depend on the specific parameters, such as exactly how many people are in a room of what size. If you fancy putting in your own data for a particular setting and activity, you can try our COVID-19 Aerosol Transmission Estimator.

Trish Greenhalgh, Professor of Primary Care Health Sciences, 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 is republished from The Conversation under a Creative Commons license. Read the original article.

One thought on “Catching COVID”

  1. Dear Darren

    Hello from the UK. Many thanks for this post. However, you can’t catch Covid 19, a.k.a. the ‘flu since re-branding in 2020. I will explain if I may.

    I used to think otherwise until, at 60 years of age in 2020, I researched properly. I changed my mind.

    Covid 19 is the ‘flu, dressed up as a monster to scare people, re-branded if you will. This helps big pharma etc, control the populace and make more money.

    The ‘flu is the internal toxicosis of the body, mainly via urea, partly due to metabolism of food and partly due to the many poisons in our environment which can and do enter our bodies in the air, food and water. The ‘flu cannot be transmitted to someone else as it is individual to each person.

    Unless your blood is given to someone in a blood transfusion, for example.

    Vitamin D deficiency is the true pandemic due to indoor working and living away from the sunshine which, if we do the right thing things, will give us vitamin D (free!). Big pharma etc. are not keen on free as they don’t make much money out of it.

    Vitamin D levels drop in the winter months due to reduced sunshine levels and as any gains in the summer months are depleted. In Australia this should not be a problem but there are lots of other ways one can get ill and there are issues with pre-existing conditions which have skewed the statistics.

    I have seen the statistics on Australia since February 2020. These show a close correlation between Covid cases and vaccination. It is abundantly clear the vaccines are causing the case numbers rise, as would be expected as these are neuro-toxins. These will give you Covid 19 or the’flu as it was known as before all the nonsense started.

    https://alphaandomegacloud.wordpress.com/2022/01/11/australia-coronavirus-statistics/

    Please note I do use humour as necessary on posts and pages to lighten the mood and help make the points.

    May I take the opportunity to wish you a very happy new year.

    Kind regards

    Baldmichael Theresoluteprotector’sson

    Please excuse the nom-de-plume, this is as much for fun as a riddle for people to solve if they wish.

    Liked by 1 person

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