Why Does Long COVID Happen? Leading Theories and the Role of Genetics

Introduction: The Short Answer

Why does Long COVID happen? Researchers do not yet have one complete answer. The current view is that Long COVID likely arises from several overlapping processes after a SARS-CoV-2 infection. These include:

• Fragments of the virus lingering in the body
• Lasting changes in the immune system
• Autoimmune reactions
• Tiny blood clots that affect circulation
• Disruption of the autonomic nervous system

Different people may experience different combinations of these mechanisms. Genetics appears to be one factor that may influence who is affected and how. It is not the whole story, but it may help explain why two people with similar infections can have very different recoveries.

If you are living with persistent symptoms, it can be frustrating that science has not settled on a single explanation. It is also reassuring that research is moving quickly. Understanding the main theories can help you have more informed conversations with your healthcare team. You can read more background on our Long COVID genetics page.

How the Mechanism Works: Main Proposed Causes

Long COVID is best understood as a group of related problems rather than a single disease process. Below are the leading hypotheses researchers are exploring.

Viral Persistence

One theory is that the virus, or pieces of it, is not fully cleared after the acute illness. Viral proteins or genetic material may remain in certain tissues. This could keep the immune system in a state of low-level activation. Ongoing activation may contribute to fatigue, brain fog and other symptoms.

Immune Dysregulation

Even without lingering virus, the immune system may not fully return to its baseline. Studies have explored altered immune cell patterns and ongoing inflammatory signalling in people with Long COVID. An immune system stuck in alert mode may affect many organs at once.

Autoimmunity

Some researchers suggest that the infection may prompt the immune system to produce antibodies that mistakenly target the body's own tissues. This kind of autoimmune response could help explain symptoms that persist long after the virus itself is gone.

Microclots and Vascular Changes

Another line of research looks at the blood vessels and blood clotting. Small, persistent clots, often called microclots, and changes to the inner lining of blood vessels have been proposed as contributors. These changes could reduce oxygen delivery to tissues, which may relate to exhaustion and exercise intolerance.

Autonomic Dysfunction

The autonomic nervous system controls automatic functions such as heart rate, blood pressure and digestion. Many people with Long COVID report symptoms like a racing heart on standing, dizziness or temperature sensitivity. These symptoms suggest this system may be disrupted after infection.

The Relevant Genes and Variants

Genetics may influence several steps in this story: how easily the virus enters cells, how strongly the early antiviral response works, and how well the body clears viral material. The genes below are areas of emerging research. Having a particular variant does not mean you will or will not develop Long COVID.

Viral Entry Genes

SARS-CoV-2 needs help from human proteins to get into cells. You can learn more on our viral entry genetics page.

• ACE2 encodes the primary entry receptor for the virus. It is also a key regulator of the renin-angiotensin system in the heart, blood vessels and lungs. Research suggests that ACE2 downregulation after infection may contribute to angiotensin II excess, vascular dysfunction and lung injury. This links it to the vascular theories described above. Variants studied include rs2285666 and rs4240157.
• TMPRSS2 encodes a protease that primes the spike protein, which helps the virus enter cells. Variants affecting entry efficiency may influence initial viral load and later immune dysregulation. Variants of interest include rs12329760 and rs2070788.
• FURIN activates the spike protein at a cleavage site that is unique to SARS-CoV-2. This step is important for efficient entry and cell-to-cell fusion. Studies have explored whether variants such as rs17514846 and rs2521501 might influence infectivity and cellular damage.

The CD147 and Cyclophilin Pathway

• BSG encodes CD147, also called basigin. It has been proposed as a co-receptor for the virus. CD147 is involved in both viral entry and inflammatory signalling. Variants such as rs8259 may affect infectivity and inflammatory responses.
• PPIA encodes cyclophilin A. During inflammation, cyclophilin A can bind CD147 and promote cell entry. Variants such as rs6850 may affect CD147-dependent entry and inflammatory cascades. This connects to the immune dysregulation theory.

Early Antiviral Defence

A strong, well-timed early response may help clear the virus before it causes lasting problems. Explore more on our antiviral response genetics page.

• IFNL1 encodes interferon lambda-1, a type III interferon that acts mainly at mucosal surfaces such as the airways. Research suggests these responses may influence early viral clearance and Long COVID susceptibility. A variant studied here is rs8103142.
• IFNL3 encodes interferon lambda-3, which is important for clearing viruses in the respiratory tract. The rs12979860 variant is among the most replicated variants linked to interferon responses. Variants including rs8099917 may influence Long COVID severity and recovery.

Clearing Viral Remnants

• IRGM encodes a protein that helps cells break down intracellular pathogens through a process called xenophagy. Research suggests that variants affecting IRGM expression, such as rs13361189 and rs4958847, may impair the clearance of SARS-CoV-2 components. This may contribute to the viral persistence described earlier.

Practical Implications

What does this mean for someone living with Long COVID? A few points are worth keeping in mind.

Genetics is one piece of a larger picture. Your genes interact with other factors that are thought to matter, including:

• The severity of your initial infection
• Prior health conditions
• Vaccination status
• Many other influences

No single variant determines your outcome.

Patterns may offer context, not conclusions. Looking at variants across viral entry, interferon response and viral clearance genes may help you understand which biological themes could be relevant to you. This is informational and can be a starting point for discussion. It is not a way to assess or identify a medical condition.

Symptoms still guide care. Whatever your genetic profile, your day-to-day experience matters most. Keeping a symptom diary, noting triggers and pacing your activity are approaches many people find helpful when talking with clinicians.

Talk to a healthcare professional. If you are interested in what your genetic data might suggest, a doctor or genetic counsellor can help you interpret it alongside your history and any test results. They can also help you plan ways to manage and support your recovery.

Why Research Is Still Evolving

Long COVID is still a relatively new condition, and many studies are small or early. Findings on individual variants may change as larger studies are completed. That is why genetic insights are best viewed as emerging evidence rather than firm answers. Staying curious and cautious is a reasonable approach.

Get Personalized DNA Insights

If you have raw data from a consumer DNA test, ChronicDNA can show which of these Long COVID-related variants appear in your results. It presents them with clear, research-based context. Your report is informational and designed to support conversations with your healthcare team. Get your ChronicDNA report