Describes a person who has been infected with a pathogen, but shows no symptoms of the disease. Most often, people who are asymptomatic are unaware that they may be spreading an infectious disease. 

In the case of COVID-19, there are widely varying estimates of the percentage of infected people who are asymptomatic, with figures ranging from 30 %to 80% of all those infected. It’s not yet certain how many people carry and transmit the virus without them ever being aware of it. One reason for this confusion is that it can be difficult to make the distinction between asymptomatic people (those who never develop symptoms) and those who are presymptomatic, meaning those who have not yet shown symptoms but will do so later.

Scientists also don’t know exactly why some people remain asymptomatic, while others die from COVID-19 disease. `Researchers suggest this could be due to differences in genetic make-up, age, and comorbid diseases. The harsh lockdowns in some countries were driven, mainly by concerns about asymptomatic people unknowingly spreading the disease and not taking protective measures.

Mary Mallon, infamously dubbed ‘Typhoid Mary’ is a historical example of an asymptomatic spreader. A domestic worker in early 20th century America, she worked for several families and unknowingly infected more than 500 people with typhoid, despite not experiencing any symptoms herself. When the cases were traced to her, she was put in isolation in a government facility and remained there for the rest of her life.



Symptoms Transmission