A helpful guide to the risks associated with Covid-19 and how to avoid them where possible

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Professor Erin Bromage, a comparative Immunologist and Professor of Biology has written a helpful guide to the risks associated with Covid-19 and how to avoid them where possible

It includes a helpful formula:

Successful Infection = Exposure to Virus x TimeBromage write: “When assessing the risk of infection (via respiration) at the grocery store or mall, you need to consider the volume of the air space (very large), the number of people (restricted), how long people are spending in the store (workers – all day; customers – an hour).”
The article addresses three key questions:

  1. Where are people getting sick?
  2. How much Virus is released into the environment?
  3. What is the role of asymptomatic people in spreading the virus?

The extensive quotation below summarises key takeaways:

  • “Indoor spaces, with limited air exchange or recycled air and lots of people, are concerning from a transmission standpoint…. The principle is viral exposure over an extended period of time. In all these cases, people were exposed to the virus in the air for a prolonged period (hours). Even if they were 50 feet away (choir or call center), even a low dose of the virus in the air reaching them, over a sustained period, was enough to cause infection and in some cases, death.”
  • “Social distancing rules are really to protect you with brief exposures or outdoor exposures. In these situations there is not enough time to achieve the infectious viral load when you are standing 6 feet apart or where wind and the infinite outdoor space for viral dilution reduces viral load. The effects of sunlight, heat, and humidity on viral survival, all serve to minimize the risk to everyone when outside.”
  • “Taken together, for a person shopping: the low density, high air volume of the store, along with the restricted time you spend in the store, means that the opportunity to receive an infectious dose is low. But, for the store worker, the extended time they spend in the store provides a greater opportunity to receive the infectious dose and therefore the job becomes more risky.”
  • “If I am outside, and I walk past someone, remember it is “dose and time” needed for infection. You would have to be in their airstream for 5+ minutes for a chance of infection. While joggers may be releasing more virus due to deep breathing, remember the exposure time is also less due to their speed. Please do maintain physical distance, but the risk of infection in these scenarios are low.”
  • “please don’t forget surfaces. Those infected respiratory droplets land somewhere. Wash your hands often and stop touching your face!”

Professor Erin Bromage is a Comparative Immunologist and Professor of Biology (specializing in Immunology) at the University of Massachusetts Dartmouth (who have covered the reaction to this article here:

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