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 kids 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 health club, or dance in a nightclub with out concern 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 data 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, akin to 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 develop into. If you are outside, the house is nearly infinite, so the virus doesn’t construct up in the identical approach. Nonetheless, 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 (akin to when exercising) or includes vocalization (akin to 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 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 depends upon 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 present contaminated (the prevalence of the illness). On the time of writing, greater than 97% of COVID infections in the UK are omicron and one individual in 15 is at present contaminated (prevalence 6.7%). Whereas omicron seems extra transmissible, it additionally appears to produce much less extreme sickness, particularly in vaccinated individuals.

Chance of turning into contaminated

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

We did this by fastidiously 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 brand new chart, tailored from our paper and proven under, provides a share probability of turning into contaminated in several conditions (you could make it larger by clicking on it).

Table showing the risk of catching COVID based on various factors.Danger of catching COVID.
Writer supplied

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A surefire approach to catch COVID is to do a mixture of issues that get you into the darkish purple cells within the desk. For instance:

  • Collect along with a number of individuals in an enclosed house with poor air high quality, akin to an under-ventilated health club, nightclub or faculty classroom
  • Do one thing strenuous or rowdy akin to exercising, singing or shouting
  • Go away off your masks
  • Keep there for a very long time.

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

  • If you should meet different individuals, accomplish that 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
  • Preserve the variety of individuals to a minimal
  • Spend the minimal attainable 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 scenario, the precise threat will depend upon the precise parameters, akin to precisely how many individuals are in a room of what dimension. If you fancy placing in your personal knowledge for a selected setting and exercise, you can attempt our COVID-19 Aerosol Transmission Estimator.