Long COVID is a clinically heterogeneous multisystem chronic disease caused by SARS-CoV-2 infection. Long COVID can affect people of all ages, including children, regardless of health or socioeconomic status, sex, sexual orientation, race, ethnic group, their geographic location, and COVID-19 vaccine status. Long COVID is recognized and diagnosed after people with Long COVID experience symptoms that are present three months, or longer, from the date of their acute infection. There can be a period of time after the acute SARS-CoV-2 infection stage, and before three months have passed, during which one is ill. 

SARS-CoV-2 is primarily transmitted through exposure to particles in the air, with aerosols being a major vessel of transmission. The virus can persist in those infected. It is also a vascular pathogen that can affect the organs and systems of the body, initiating complex pathophysiological responses, leading to damage in, but not limited to: the heart, lungs, digestive system, brain, kidneys, liver, pancreas, the neurological system, and reproductive system.

People with Long COVID can experience consistent, changing, or waxing and waning of any of more than 200 symptoms, which can migrate from area to area of the body. The symptoms can evolve, shift, relapse, remit, persist, and progress. Symptoms can be uninterrupted from the moment of acute SARS-CoV-2 infection or have a delayed onset, emerging several months or longer after initial infection and apparent recovery. There is no hallmark symptom of Long COVID. Long COVID can damage various organs and systems of the body, cause mitochondrial dysfunction, and immune dysfunction and dysregulation. Long COVID can shorten lives and be fatal.
 
Research shows that SARS-CoV-2 can persist. The virus, and its components, such as the spike protein, have the ability to linger in different parts of the body for long periods of time (potentially indefinitely). 

Inadequate and dysfunctional antibody responses have been documented in a portion of people with Long COVID. Additionally, reactivation of latent viruses, or the appearance of secondary infections, such as: EBV, CMV, HHV-6, VZV, and others, including non-viral pathogens, can occur. 

Long COVID can cause, but is not limited to causing: thromboinflammation, hematological disorders, immune dysregulation (including autoimmunity), and a range of other issues. These can cause organ damage, and other damage, leading to both new and worsening symptoms that can impact long-term health. 

Notably, repeat SARS-CoV-2 infections can exacerbate existing Long COVID symptoms, cause new symptoms, and additional organ damage, further complicating the clinical picture.

Common and serious symptoms include, but are not limited to: brain dysfunction (including difficulty with concentration and memory), headaches or migraines, lightheadedness, dizziness, tachycardia, bradycardia, tinnitus, dyspnea, problems with taste or smell, cough, persistent and debilitating fatigue, chest pain, sleep disturbance, eye and vision issues (dry eyes), post-exertional malaise, gastrointestinal issues (bloating, constipation, diarrhea), menstrual changes, skin manifestations/rashes, vocal issues, oral problems (including tooth loss), and joint, muscle, and organ pain. 

Conditions and diseases that can occur due to Long COVID include, but are not limited to: cancer (SARS-CoV-2 awakens and expands previously seeded dormant cancer cells, etc.),  interstitial lung disease and hypoxemia, asthma/asthma-like symptoms, cardiovascular disease and arrhythmias, myocarditis/pericarditis, heart failure, heart attack, cognitive impairment, neurological disorders/brain damage (neuroimaging studies have found gray matter loss, microstructural changes, and neuroinflammation in Long COVID patients), mood disorders/anxiety/depression (can be pathophysiologically caused), strokes, blood clots (including deep vein thrombosis, pulmonary embolisms, microclots affecting circulation), hypertension, lymphopenia, alopecia, chronic kidney disease, mast-cell activation syndrome (MCAS), allergies, connective-tissue diseases, hyperlipidemia, diabetes, seizures, dementia, sleep apnea, gastrointestinal conditions (irritable bowel syndrome (IBS), nutrient malabsorption, food intolerance), fatty liver, dysautonomia, adrenal insufficiency, and autoimmune disorders. 

Autoimmune illnesses including, and not limited to: lupus, rheumatoid arthritis, inflammatory bowel disease (IBD) (chronic colitis, Crohn's disease), Guillain-Barré syndrome (GBS), Raynaud’s disease, Hashimoto’s disease, IgA nephropathy, and Sjögren’s syndrome. Some of the symptoms of Long COVID are also similarly experienced by those diagnosed with other conditions, including various symptomatic syndromes.

It is important to remember that Long COVID has distinct characteristics and risks that require treatments tailored to its pathophysiology. A Long COVID diagnosis (or a diagnosis with a code that goes by a name used by the government that they use interchangeably with Long COVID) is crucial in those who have the disease.

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Additional Long COVID Traits:
* Long COVID can occur following asymptomatic, mild, or severe acute SARS-CoV-2 infection. The initial infection may have been undetected due to lack of testing or a false negative, therefore, a positive test should not be considered the only prerequisite for diagnosis.

* Long COVID can exacerbate preexisting health conditions or manifest as new ones, even ones that go unrealized and would go unidentified without adequate laboratory testing, or even despite undergoing extensive lab testing. 
* Long COVID can range from mild to severe. Some patients experience gradual improvement over time. Long COVID symptoms can persist, fluctuate, and worsen over the course of months or years, possibly indefinitely without proper treatment.
* While there are tests that can identify various downstream effects, there are currently no approved biomarkers or tests. Long COVID can be diagnosed on clinical grounds. Underdiagnosis of Long COVID is a significant concern.
* Long COVID is recognized under the Americans with Disabilities Act (ADA), when it substantially limits one or more major life activities. Long COVID can disrupt a person's ability to work, attend school, and look after their family and themselves. This can result in a substantial reduction in quality of life. Children suffering from Long COVID can experience adverse effects on their quality of life and long-term health impacting both their childhood and future.
* Long COVID can impair multiple body systems including, but not limited to: the immune, nervous, gastrointestinal, and vascular systems.
* People with Long COVID have been found to exhibit persistent gut microbiome dysbiosis, including reduced microbial diversity and depletion of beneficial bacteria.
* People with Long COVID may experience altered cytokine production, severe and chronic inflammation, mitochondrial dysfunction, evidence of accelerated biological aging, endothelial dysfunction, and immune dysregulation affecting B cells and T cells (including T cell exhaustion and functional alterations in CD4 and CD8 T cells). These changes may leave those with Long COVID vulnerable to opportunistic infections. 

Although exact numbers of those living with the condition are uncertain, it is estimated that more than 400 million worldwide have experienced Long COVID (underestimate). There are estimates of 54 million+ COVID Long Haulers in the United States alone (and probably more due to conservative estimates or underestimates). It's very difficult to get extremely accurate statistics due to a lack of good diagnostics for Long COVID and failure to identify initial COVID infection in many people. It is a tremendous, wide reaching problem, that's only increasing with every wave, which can occur any time of the year. Good SARS-CoV-2 antivirals need to be developed to combat this fast growing issue. In the mean time taking every precaution reasonably possible is best.