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Where and how you are most likely to catch COVID

By Trish Greenhalgh and Jose-Luis Jimenez and Shelly Miller and Zhe Peng—The Conversation 4 minute Read

Against this bleak image, we yearn to get again to regular. We’d like to meet pals in a pub or have them over for dinner. We’d like our struggling enterprise to thrive prefer it did earlier than the pandemic. We’d like our youngsters to return to their once-familiar routine of in-person education and after-school actions. We’d like to experience on a bus, sing in a choir, get again to the gymnasium, or dance in a nightclub with out worry of catching COVID.

Which of those actions is protected? And how protected, precisely? These had been the questions we sought to reply in our latest research.

SARS-CoV-2, the virus that causes COVID, spreads primarily by airborne transmission. So, the important thing to stopping transmission is to perceive how airborne particles behave, which requires information from physics and chemistry.

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Air is a fluid made up of invisible, quickly and randomly shifting molecules, so airborne particles disperse over time indoors, comparable to in a room or on a bus. An contaminated particular person might exhale particles containing the virus, and the nearer you are to them, the extra likely you are to inhale some virus-containing particles. But the longer the interval you each spend within the room, the extra unfold out the virus will change into. If you are outdoor, the house is sort of infinite, so the virus doesn’t construct up in the identical method. However, somebody can nonetheless transmit the virus if you’re shut to them.

Viral particles will be emitted every time an infected person breathes, however particularly if their respiration is deep (comparable to when exercising) or entails vocalization (comparable to when talking or singing). While wearing a well-fitting mask reduces transmission as a result of the masks blocks the discharge of the virus, the unmasked contaminated one who sits quietly in a nook is way much less likely to infect you than one who approaches you and begins a heated argument.

All variants of SARS-CoV-2 are equally airborne, however the probability of catching COVID relies on the transmissibility (or contagiousness) of the variant (delta was extra contagious than earlier variants, however omicron is extra contagious nonetheless) and on how many individuals are at the moment contaminated (the prevalence of the illness). At the time of this writing, greater than 97% of COVID infections in the U.K. are omicron, and 1 particular person in 15 is at the moment contaminated (prevalence 6.7%). While omicron seems extra transmissible, it additionally appears to produce much less extreme sickness, particularly in vaccinated folks.

Likelihood of changing into contaminated

In our research, we’ve quantified how the totally different influences on transmission change your danger of getting sick: viral elements (transmissibility/prevalence), folks elements (masked/unmasked, exercising/sitting, vocalizing/quiet), and air-quality elements (indoors/outdoor, large room/small room, crowded/uncrowded, ventilated/unventilated).

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We did this by rigorously learning empirical knowledge on how many individuals turned contaminated in superspreader occasions the place key parameters, such because the room dimension, room occupancy, and air flow ranges, had been well-documented and by representing how transmission occurs with a mathematical mannequin.

The new chart, tailored from our paper, and proven under, offers a proportion probability of changing into contaminated in numerous conditions (you could make it greater by clicking on it).

Table showing the risk of catching COVID based on various factors.Risk of catching COVID. [Chart: Author provided]

A surefire method to catch COVID is to do a mix of issues that get you into the darkish pink cells within the desk. For instance:

  • Gather along with numerous folks in an enclosed house with poor air high quality, comparable to an underventilated gymnasium, nightclub, or college classroom
  • Do one thing strenuous or rowdy comparable to exercising, singing, or shouting
  • Leave off your masks
  • Stay there for a very long time

To keep away from catching COVID, attempt preserving within the inexperienced or amber areas within the desk. For instance:

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  • If you should meet different folks, achieve this outdoor or in an area that’s well-ventilated, or meet in an area the place the air flow is sweet and air high quality is understood
  • Keep the variety of folks to a minimal
  • Spend the minimal potential period of time collectively
  • Don’t shout, sing, or do heavy train
  • Wear high-quality, well-fitting masks from the time you enter the constructing to the time you depart

While the chart offers an estimated determine for every state of affairs, the precise danger will rely upon the precise parameters, comparable to precisely how many individuals are in a room of what dimension. If you fancy placing in your personal knowledge for a specific setting and exercise, you can attempt our COVID-19 Aerosol Transmission Estimator.

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