Information You Need: Duration x Viral Shedding Level x Contact Distance = Infection

What do the terms duration and “distance” and “viral shedding level” mean?

  • Viral shedding level – means the level of virus that the person you are in contact with is shedding or putting out into the air
  • Contact distance means the intimacy of the contact you have – how far are you away from them.
  • Duration means the amount of time that you have been exposed to an infected person.

What is needed for an infection to occur?

  • The recipe for a viral infection requires several things: contact with an infected person, the amount of virus they were shedding at the time and the amount of time exposed. When someone becomes infected with a virus it means they were exposed to enough viral particles for a long enough amount of time to cause an infection.

How does this apply to COVID-19?

  • For the COVID-19 virus, those particles are mainly spread through respiratory droplets that are produced by breathing, talking, sneezing, and coughing. This means that if you are in close contact (within 6 feet) with someone who is currently infected with COVID-19 (whether they are showing symptoms or not), you are most likely breathing in their respiratory droplets. However, for you to become infected you must be in close contact with an infected person for long enough to inhale enough viral particles needed to make you sick. 
  • COVID-19 virus can spread over longer distances so even if you are six feet away from someone there is a chance you can still become infected. This transmission is called airborne transmission. This happens more when you are indoors, in a small room without good ventilation, cold conditions and when the person who is sick is breathing hard, coughing or singing. All of those things help the virus get into and stay in the air.

A general formula for infection is: Duration x Viral Shedding Level x Contact Distance

  • This amount of virus is called the minimum infectious dose and it varies by the type of virus and characteristics of the person. 
  • The amount of viral particles that will cause illness is different for everyone. For example, those who are more susceptible (e.g., older adults and immunocompromised individuals) to the virus can breathe in fewer particles than those less susceptible and still get infected. This means that they would need less time around someone who was infected to catch the virus compared to someone who is not part of a high-risk group for COVID-19.
  • With certain diseases, we know that an exposure can be directly related to disease severity. In other words, more exposure to the virus can mean a more serious case of the disease. Scientists are exploring whether or not this is true for COVID-19. 

To reduce the risk of developing COVID-19 you should:

  1. Reduce your exposures 
  1. Reduce the duration of time you are around people
  • Lessening the duration of time you spend around others will reduce the likelihood of inhaling enough viral particles to make you sick. 
  • For example, if you don’t like ordering groceries because you like picking your produce, order everything else for grocery store pick-up and then go inside for a shorter duration to get your produce.

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