About Long COVID

If you experience long-lasting symptoms after a COVID-19 infection , this is often referred to as Long COVID . Here, ' Long ' means 'long-lasting', but it has nothing to do with your lungs . The WHO now refers to it as post-COVID-19, because the long-lasting symptoms occur after an infection with COVID-19 ('post' means 'after'). Other terms used are PASC (Post-acute sequelae of SARS-CoV-2 infection ) and PCS (post-COVID syndrome). C-support usually uses the term post-COVID.

Common complaints
The most common complaints are: Exhausting fatigue, nnot being able to concentrate well, vforgetfulness, brain fog, osensitivity to light and sound, kshortness of breath, hheadache, sirritability, ssleep well, spain in the neck and ddizziness. Specific symptom clusters are also common, such as post-exertional malaise (PEM) en postural orthostatic tachycardia syndrome (POTS), an expression of dysautonomiaIn addition, people with post-COVID may also experience mast cell activation syndrome (MCAS)In total there are over 200 symptoms described. 

It's not entirely clear how many people have post-COVID-19. This is due to:

• The number of symptoms that can occur. This can result in post-COVID-19 not being recognized and/or a different diagnosis being made.
• The lack of complete registration of these patients.  

Various studies provide estimates regarding the number of people with post-COVID. The figures on this vary, as they depend on the definition, research method, and population characteristics used. The Lifelines study (2022) shows that 1 in 8 Dutch people who became infected experience long-term symptoms (12,5%). RIVM figures (2024) show that 4% of adults reported having long-term symptoms possibly caused by the coronavirus. This is in contrast to other national and international studies, which report higher estimates.

The MIT report (2023) assumes there are 450.000 patients in the Netherlands, of whom 90.000 have severe long-term symptoms. This also includes children and adolescents.

Since October 2020, over 33.000 people have contacted C-support seeking advice and support regarding their complaints. We offer advice on physical complaints , psychosocial problems , and issues related to work and income.

C-support will cease operations at the end of 2026, therefore it is unfortunately no longer possible to register.

Multiple studies show possible risk factors that increase the likelihood of developing post-COVID symptoms.

One-third of people with post-COVID appear to have been healthy prior to the infection and not to suffer from chronic conditions** . Little is known yet about how the various risk factors relate to the different phenotypes or manifestations of post-COVID.

** source review in Nature (English) and Post-COVID knowledge compilation of the IVM and C-support

Extensive research is being conducted to clarify the possible causes of post-COVID. Various ( international) studies have now described multiple theories indicating what might be happening in the body in the case of post-COVID symptoms . Biomedical research is also providing increasing evidence for this . A growing correlation is also being found between various post-infectious conditions. Examples include Q fever, Lyme disease , sepsis , and ME/CFS.

Most frequently mentioned, partly overlapping, theories about post-COVID

• Viral causes, including persistent viral persistence and/or reactivation of underlying pathogens
  Viral particles may remain present in the body (persistence). These viral particles remain in various organs, which can lead to tissue damage and persistent symptoms. In addition, an infection can also lead to the reactivation of previous infections (reactivation), including (often harmless) infections experienced earlier in life.
• Oregulation of the immune system
  There are indications of a dysregulation of the immune system. The innate immune system continues to fight against any viral particles present, meaning the immune system is essentially in a permanent "on" state. The immune system is then overactive, and abnormalities in the immune response can occur. For example, due to a shortage of certain immune cells or insufficient antibody production. This can cause the body to respond inadequately during an acute infection.A dysregulation of the immune system can also lead to misprogramming of immune cells, causing the immune system to attack the body's own cells (autoimmunity). These abnormalities can cause the body to harm itself, even without the virus present. This results in persistent inflammation and numerous symptoms.
• Endothelial damage and thrombosis
  The virus can damage the walls of blood vessels, causing inflammation in the small blood vessels. This can lead to the blockage of capillaries by 'micro-clots'. This can cause poor blood flow in the vessels, making it difficult for nutrients and oxygen to be supplied. This can cause damage to nerves and muscles and, moreover, poses an increased risk of cardiovascular disease for up to a year after a COVID-19 infection.

Other theories

In addition to the three theories mentioned above, several other processes have been described that likely play a role in post-COVID-19. These appear to be less well-described and researched and appear to be primarily secondary to the above-mentioned primary theories. Examples include:  

• Autonomic dysregulation; dysfunctional signal processing in the brainstem
  Signal transmission in the nervous system regulates the balance between suppressing and activating unconscious processes such as heart rate, blood pressure, breathing, digestion, and temperature. Due to the toxicity (direct damage) of the virus to the nervous tissue, the nervous system becomes significantly disrupted. Often, neurological symptom patterns emerge over time, such as orthostatic intolerance (OI) (including POTS), gastrointestinal complaints and extreme fatigue.
• Mitochondrial abnormalities
  Mitochondria are the tiny energy factories in your cells. In post-COVID times, there are indications that mitochondria function less efficiently. The resulting lack of energy contributes to severe fatigue and exercise intolerance. Furthermore, the lack of sufficient oxygen can lead to additional tissue damage and inflammatory processes. The lack of healthy mitochondria slows recovery and leads to muscle acidification, resulting in symptoms such as muscle weakness and soreness.
• Disturbed balance in the intestines ('dysbiosis') 
  The body's own gut bacteria play a vital role in maintaining the body's balance. A new parasite, bacterium, or virus can disrupt this delicate balance, leading to inflammation of the gut flora. In some cases, this inflammation persists in the intestinal tissue, potentially contributing to a variety of symptoms throughout the body.
• Misfolding due to viral proteins
  Viral proteins can cause the body's own proteins to misfold. These misfolded proteins can clump together and form insoluble fibers. This can gradually damage or kill nerve cells in the brain and spinal cord.
• Disrupted hormonal system 
  Hormonal abnormalities have been demonstrated in post-COVID-19, such as lower cortisol levels and changes in growth hormone. Other hormone systems may also be involved, such as an effect on the pituitary gland, including the thyroid, and sex hormones. Hormonal changes contribute to fatigue and other symptoms.  

Cause and effect

The various theories are not independent of each other. However, the distinction between cause and effect, and the connections between the various theories, are not yet clear. In almost all theories, however, the immune system plays a central role. Disruptions in this system can lead to abnormalities and symptoms in various other (organ) systems in the body. Furthermore, it is not sufficiently known to what extent different bodily systems are related to the different manifestations (phenotypes) of post-COVID-19, and whether these are comparable between adults and children. 

What are phenotypes?

There are significant differences in the symptoms of post-COVID patients. Researchers want to distinguish the diverse range of symptoms patients experience as a specific manifestation of post-COVID, a phenotype, or a subtype. This may then lead to the development of specific approaches and/or treatments for each phenotype. 

Much remains unknown regarding post-COVID. Research is increasingly being conducted both in the Netherlands and internationally. You can find information on ongoing and completed studies on various pages. PostCovid NL has a selection of published studies on their website . There is also a lot of information on the C-support PCNN page regarding Research & Updates . ZonMw provides information on research programs and on the various studies/projects currently taking place.

• PEM & POTS in Long COVID (Nov 2025) (for general practitioners)
• Overarching knowledge agenda post-COVID
• Updated knowledge agenda for biomedical research post-COVID (April 2025)
• Post-COVID knowledge bundling update (March 2025)
• Article Cell – Mechanisms of long COVID and the path toward therapeutics (Oct 2024) on underlying theories surrounding post-COVID 
• Review Nature Magazine – Long COVID science, research and policy | update (Aug 2024) 
• Article Science Direct – Skeletal muscle adaptations and post-exertional malaise in long COVID (July 2024) 
• Public version of the report on the knowledge agenda for biomedical research post-COVID (Nov 2023)
• Post-COVID grassroots consultation report (Nov 2023)
• Report on the knowledge agenda for biomedical research post-COVID (Oct 2023)
• Report Knowledge bundling of ongoing (inter)national research post-COVID (Sept 2023)
• Review Nature Magazine – Long COVID: major findings, mechanisms and recommendations (July 2023) on underlying theories surrounding post-COVID 
• Review Nature Magazine – Unexplained post-acute infection syndromes (May 2022) 
• NASA Lean Test (Bateman Horne Centre, USA)
• Podcast Prisma: what is post-COVID (for general practitioners)
• Webinar post-COVID complaints in general practice (medical education)
• Research consortium Long COVID Foundation
• Post-COVID care research – C-support (March 2025) (Delphi study C-support)

What is known about complaints after COVID-19 vaccination 

• Yale study – preprint, Immunological and Antigenic Signatures Associated with Chronic Illnesses after COVID-19 Vaccination (Feb 2025) 
• Article MDPI – Clinical and Diagnostic Features of Post-Acute COVID-19 Vaccination Syndrome (PACVS) (June 2024)