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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 Dialog 4 minute Learn

Towards this bleak image, we yearn to get again to regular. We’d like to meet mates 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 journey 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 secure? And how secure, 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.


Air is a fluid made up of invisible, quickly and randomly transferring molecules, so airborne particles disperse over time indoors, reminiscent of in a room or on a bus. An contaminated individual could exhale particles containing the virus, and the nearer you are to them, the extra likely you are to inhale some virus-containing particles. However the longer the interval you each spend within the room, the extra unfold out the virus will change into. If you are outside, the area is nearly infinite, so the virus doesn’t construct up in the identical manner. Nonetheless, somebody can nonetheless transmit the virus if you’re shut to them.

Viral particles may be emitted every time an infected person breathes, however particularly if their respiratory is deep (reminiscent of when exercising) or entails vocalization (reminiscent of when talking or singing). Whereas 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 far 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 likelihood of catching COVID will depend 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). On the time of this writing, greater than 97% of COVID infections in the U.K. are omicron, and 1 individual in 15 is at the moment contaminated (prevalence 6.7%). Whereas omicron seems extra transmissible, it additionally appears to produce much less extreme sickness, particularly in vaccinated folks.

Probability of changing into contaminated

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


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

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

Threat of catching COVID. [Chart: Author provided]

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

  • Collect along with numerous folks in an enclosed area with poor air high quality, reminiscent of an underventilated gymnasium, nightclub, or faculty classroom
  • Do one thing strenuous or rowdy reminiscent of exercising, singing, or shouting
  • Depart off your masks
  • Keep there for a very long time

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

  • If you should meet different folks, achieve this outside or in an area that’s well-ventilated, or meet in an area the place the air flow is nice and air high quality is understood
  • Maintain the variety of folks to a minimal
  • Spend the minimal doable period of time collectively
  • Don’t shout, sing, or do heavy train
  • Put on high-quality, well-fitting masks from the time you enter the constructing to the time you go away

Whereas the chart provides an estimated determine for every state of affairs, the precise threat will depend upon the precise parameters, reminiscent of precisely how many individuals are in a room of what measurement. If you fancy placing in your individual knowledge for a selected setting and exercise, you can attempt our COVID-19 Aerosol Transmission Estimator.

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