What Is Long COVID?

Long COVID, also known as Post-COVID-19 Condition or Post-Acute Sequelae of SARS-CoV-2 infection (PASC), refers to a set of symptoms that persist, return, or newly appear after the acute phase of a COVID-19 infection. These symptoms can last for weeks, months, or even years, and they can occur regardless of how mild or severe the initial infection was.

According to the U.S. Centers for Disease Control and Prevention (CDC), Long COVID is defined as symptoms, conditions, or health problems that continue or develop four or more weeks after a person is first infected with the virus that causes COVID-19. Importantly, there is no single test that can diagnose Long COVID, and symptoms can vary widely from person to person.

Long COVID is not rare. Estimates vary depending on the study and population, but millions of people worldwide are believed to be living with Long COVID today. In the United States alone, surveys suggest that several million adults have experienced prolonged symptoms following COVID-19. Children and adolescents can also develop Long COVID, although rates appear lower than in adults.

What Does Long COVID Feel Like?

Long COVID is not one uniform illness. It is better understood as a spectrum of overlapping symptoms that can affect multiple organ systems at the same time. Many people experience profound fatigue that is not relieved by rest and worsens after physical or mental exertion. Cognitive symptoms such as brain fog, difficulty concentrating, memory problems, and slowed thinking are also common.

Other frequently reported symptoms include shortness of breath, chest pain, heart palpitations, dizziness, headaches, sleep disturbances, gastrointestinal problems, muscle or joint pain, sensory sensitivities, and changes in heart rate or blood pressure, many of which are related to the autonomic nervous system (dysautonomia). Some people experience fluctuations, where symptoms improve for a time and then return or worsen.

For many patients, Long COVID significantly interferes with daily functioning, work, and quality of life. In more severe cases, people may become partially or fully disabled.

Long COVID shares features with several other chronic conditions, and many patients meet diagnostic criteria for one or more of them.

One such condition is Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS). ME/CFS is characterized by severe fatigue, post-exertional malaise (a worsening of symptoms after activity), unrefreshing sleep, and cognitive dysfunction. A substantial subset of people with Long COVID experience symptoms that closely resemble ME/CFS, and some researchers believe Long COVID may trigger ME/CFS in susceptible individuals.

Another commonly overlapping condition is Postural Orthostatic Tachycardia Syndrome (POTS), a form of autonomic nervous system dysfunction. People with POTS may experience rapid heart rate upon standing, dizziness, fainting, fatigue, and brain fog. Autonomic dysfunction appears to be relatively common in Long COVID.

Mast Cell Activation Syndrome (MCAS) is also frequently discussed in the context of Long COVID. MCAS involves inappropriate activation of mast cells, which play a role in immune and allergic responses. Symptoms can include flushing of the skin, gastrointestinal distress, allergic-type reactions such as hives, and cardiovascular instability. While the relationship between Long COVID and MCAS is still being studied, immune dysregulation affecting mast cells is one area of active research.

These overlaps do not mean that Long COVID is identical to these conditions, but they highlight shared biological pathways that may help explain symptoms and guide research.

Why Does Long COVID Happen?

Researchers do not yet fully understand why some people develop Long COVID while others recover completely. However, several leading scientific theories are being actively investigated.

One theory is that COVID-19 disrupts normal immune system communication. This disruption may cause immune cells to mistakenly attack the body’s own tissues, resulting in autoimmune-like reactions. Evidence of autoantibodies and immune imbalance has been observed in some Long COVID patients.

Another hypothesis is that COVID-19 can reactivate dormant viruses that remain in the body after earlier infections. Viruses such as Epstein-Barr virus are known to persist in a latent state, and immune stress from COVID-19 may allow them to become active again, potentially contributing to ongoing symptoms.

There is also growing interest in the role of the gut. COVID-19 can alter the gut microbiome, and some studies suggest that viral particles or viral remnants may persist in the gastrointestinal tract. This could lead to chronic immune activation or inflammation that affects the rest of the body.

Vascular involvement is another important area of study. COVID-19 can damage the cells that line blood vessels, potentially impairing blood flow and oxygen delivery to tissues. This may help explain symptoms such as fatigue, brain fog, and exercise intolerance.

Finally, researchers are examining the impact of COVID-19 on the autonomic nervous system, including the brainstem and the vagus nerve, which regulate automatic bodily functions such as heart rate, blood pressure, and digestion. Disruption in these systems could explain symptoms like dizziness, heart palpitations, and temperature regulation problems.

It is likely that Long COVID does not have a single cause, but instead arises from a combination of biological mechanisms that differ between individuals.

Is There a Cure?

At this time, there is no known cure for Long COVID. Treatment focuses on managing symptoms, improving function, and preventing symptom worsening. Research into potential therapies is ongoing, and clinical trials are actively exploring antiviral treatments, immune-modulating therapies, and supportive interventions.

Because Long COVID affects people differently, care is often individualized. What helps one person may not help another, and some interventions can worsen symptoms if not carefully tailored.

Who Is at Risk?

Anyone who has had COVID-19 can develop Long COVID, including people who were young, previously healthy, or only mildly ill. Some studies suggest that women, older adults, and people with certain pre-existing health conditions may be at higher risk, but Long COVID has been observed across all demographics.

Reinfections may increase risk, and vaccination appears to reduce, but not eliminate, the likelihood of developing Long COVID.

How Long Does Long COVID Last?

The duration of Long COVID varies widely. Some people gradually improve over months, while others experience persistent or fluctuating symptoms for years. Recovery is not always linear, and relapses can occur, especially after physical or cognitive exertion or new infections.

Because Long COVID is still a relatively new condition, long-term outcomes are not yet fully understood.

Care, Treatment, and Support

Care for Long COVID often involves symptom management, pacing strategies to avoid overexertion, treatment of specific complications, and support for mental health and quality of life. Multidisciplinary care is often beneficial, but access to knowledgeable providers remains uneven.

Patients are encouraged to work with healthcare professionals who are familiar with Long COVID and to be cautious with interventions that promise rapid cures.

Why This Page Exists

The science of Long COVID is evolving rapidly, but most research is written for medical and biological specialists. Even for people with a scientific background, it can take years to piece together what the research is actually saying.

This site exists to make that research more accessible. By translating new studies into clear, plain-language summaries, The Long Haul aims to help people better understand what is known, what remains uncertain, and how the scientific picture is developing.

This page is not medical advice. It is a starting point: for learning, for context, and for making sense of a complex and still-unfolding condition.