How much exposure to COVID-19 does it take to infect someone?  

Posted on April 16, 2020 by Tomas Rapaport


We don’t know what degree of exposure will definitely infect someone, however; we have a broad understanding of how the virus is transmitted and which people are most likely to become infected.

I.   How the virus is transmitted:

  • The WHO states that SARS-Cov-2 virus is primarily transmitted via respiratory droplets and physical/surface contact (1)
  • Droplet transmission occurs when a symptomatic person is within 1-2 meter of another person’s mucosae or conjunctiva (1)
  • Droplets can land on objects in the immediate environment and remain viable for hours to days on depending on the type of surface (2)
  • The droplets are not inherently airborne, however; certain aerosol generating medical procedures (AGMPs) can cause airborne transmission to those in the vicinity (1) 
  • Viable virus has been found in patient’s feces, however; this does not appear to be a significant driver of transmission (3)
  • Asymptomatic infection has been reported in case studies of people in very close proximity, it is hypothesized that it is not a significant driver of transmission, although more evidence is needed to ascertain this (3,4) 

II.   Although we don’t know what degree of exposure will definitely infect someone, the WHO (5) currently defines a positive contact as:

A person who experienced ANY of the following exposures during 2 days before and 14 days after the onset of symptoms of a probable or confirmed COVID-19 case:

  1. Face-to-Face contact within 1 meter AND for more than 15 minutes
  2. Any direct physical contact
  3. Direct care for of patient without proper PPE
  4. Other situations relevant to your local risk assessment

Note: for confirmed asymptomatic cases, the period of contact is measured from 2 days before and 14 days after the date the positive sample was collected

5. Positive contacts should self isolate for 14 days and self monitor for development of symptoms (6)

Questions? Comments? Does this need to be updated? Do you have valuable points to add ? Please email



The above is intended to serve as a rapidly-created, accessible source of information curated by medical students and healthcare professionals. It is for educational purposes only and is not a complete reference resource. It is not professional medical advice, and is not a substitute for the discretion, judgment, and duties of healthcare professionals. You are solely responsible for evaluating the information above.