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What causes Long COVID?

Long COVID syndrome describes the signs and symptoms which develop following a COVID-19 infection and persist for more than 12 weeks. We don’t yet understand the mechanisms causing these symptoms; or why they only affect some people; or why they affect those people in different ways.

There may be several mechanisms explaining Long COVID symptoms. Some current hypothesis/possible ideas are described below (please be aware none of these are confirmed at present and research is ongoing):

Immune system disruption: One theory is that COVID-19 has caused the immune cells to stay activated even after the virus is gone. Some scientists are investigating if this immune response is being directed to the body itself leading to symptoms. These are sometimes referred to as autoimmune reactions.  

Circulatory effects: The lining of our blood vessels serves many purposes such as allowing passage of nutrients and oxygen and allowing immune cells to pass and stopping bleeding after an injury. One theory is that in people with Long COVID there is change to the blood vessel lining and/ or changes to clotting signals in the blood- increasing the possibility of poor circulation of nutrients and oxygen to some tissues.  

Mitochondrial dysfunction: Mitochondria are often referred to as the ‘powerhouse’ of the cell and are how the cells in our bodies make energy. One theory is that this process has been affected, leading to the varied symptoms we see in Long COVID patients. 

Inflammation as a direct result of the early COVID-19 infection: Your body will try to clear the virus by sending lots of immune cells to attack it. To do this it increases inflammation. After clearing the virus, it can be difficult for the inflammation to completely recover. This can lead to ongoing symptoms such as breathlessness or chest discomfort if the inflammation is persisting in the heart or lungs for example.  

Dysautonomia: The COVID-19 infection has led to changes to the way our Autonomic nervous system manages our unconscious bodily functions, and this causes symptoms. See “Autonomic symptoms” leaflet for more information.

Page last updated: 21 May 2024

Review due: 31 October 2025