Long COVID


Long COVID or long-haul COVID is a group of health problems persisting or developing after an initial period of COVID19 infection. Symptoms can last weeks, months, or years and are often debilitating. The World Health Organization defines long COVID as starting three months after the initial COVID19 infection, but other agencies define it as starting at four weeks after the initial infection.
Long COVID is characterised by a large number of symptoms that sometimes disappear and then reappear. Commonly reported symptoms of long COVID are fatigue, memory problems, shortness of breath, and sleep disorder. Several other symptoms, including headaches, mental health issues, initial loss of smell or taste, muscle weakness, fever, and cognitive dysfunction may also present. Symptoms often get worse after mental or physical effort, a process called post-exertional malaise. There is a large overlap in symptoms with myalgic encephalomyelitis/chronic fatigue syndrome.
The causes of long COVID are not understood. Hypotheses include lasting damage to organs and blood vessels, problems with blood clotting, neurological dysfunction, persistent virus or a reactivation of latent viruses and autoimmunity. Diagnosis of long COVID is based on COVID19 infection or symptomsand by excluding alternative diagnoses.
As of 2024, the prevalence of long COVID is estimated to be about 6–7% in adults, and about 1% in children. Prevalence might be reduced after vaccination. Risk factors include but are not limited to: higher age, female sex, having asthma, and a more severe initial COVID19 infection. Anyone can develop long COVID., there are no validated effective treatments. Management of long COVID depends on symptoms. Rest is recommended for fatigue and pacing for post-exertional malaise. People with severe symptoms or those who were in intensive care may require care from a team of specialists. Most people with symptoms at 4 weeks recover by 12 weeks. Recovery is slower for those still ill at 12 weeks. For a subset of people, for instance, those meeting the criteria for ME/CFS, symptoms are expected to be lifelong.
Globally, over 400 million people have experienced long COVID. Long COVID may be responsible for a loss of 1% of the world's gross domestic product.

Classification and terminology

Long COVID is a patient-created term coined early in the pandemic by those suffering from long-term symptoms. While long COVID is the most prevalent name, the terms long-haul COVID, post-COVID19 syndrome, post-COVID19 condition, post-acute sequelae of COVID19, and chronic COVID syndrome are also in use.
Long COVID may not be a single disease or syndrome. It could be an umbrella term including permanent organ damage, post-intensive care syndrome, post-viral fatigue syndrome and post-COVID syndrome.

Definitions

There are multiple definitions of long COVID, depending on country and institution. The most accepted is the World Health Organization definition.
The definitions differ in when long COVID starts, and how long persistent symptoms must have lasted. For instance, the WHO puts the onset of long COVID at three months post-infection, if there have been at least two months of persistent symptoms. In contrast, the US Centers for Disease Control and Prevention puts the onset of "Post-COVID Conditions" at four weeks "to emphasize the importance of initial clinical evaluation and supportive care during the initial 4 to 12 weeks after acute COVID19" According to the US National Institutes of Health, postacute sequalae of SARS-CoV-2 refers to ongoing, relapsing, or new symptoms, or other health effects that occur four or more weeks after the acute phase of SARS-CoV-2 infection.
The British National Institute for Health and Care Excellence divides long COVID into two categories:
  • ongoing symptomatic COVID19 for effects from four to twelve weeks after onset, and
  • post-COVID19 syndrome for effects that persist 12 or more weeks after onset.
The clinical case definitions specify symptom onset and development. For instance, the WHO definition indicates that "symptoms might be new onset following initial recovery or persist from the initial illness. Symptoms may also fluctuate or relapse over time."
The NICE and WHO definition further require the exclusion of alternative diagnoses.
Specifically for children and young people, a group of experts in the UK have published the only research definition which complements the clinical case definition in adults proposed by the WHO. This consensus research definition for long COVID in children and young people is: "Post COVID19 condition occurs in young people with a history of confirmed SARS-CoV-2 infection, with at least one persisting physical symptom for a minimum duration of 12 weeks after initial testing that cannot be explained by an alternative diagnosis. The symptoms have an impact on everyday functioning, may continue or develop after COVID infection, and may fluctuate of relapse over time. The positive COVID19 test referred to in this definition can be a lateral flow antigen test, a PCR test or an antibody test."

Related illnesses

Long COVID is a post-acute infection syndrome and shares similarities with other such syndromes. For instance, there are similarities with post-Ebola syndrome and aftereffects of the chikungunya virus. These conditions may have similar pathophysiology to long COVID.
Long COVID has many symptoms in common with myalgic encephalomyelitis/chronic fatigue syndrome and research estimates half of people with long COVID meet ME/CFS diagnostic criteria. Like long COVID, ME/CFS is often triggered by infections, and some biological changes overlap. Dysautonomia and postural orthostatic tachycardia syndrome are also potential shared aspects of long COVID and ME/CFS. However, long COVID symptoms include loss of smell and taste, neither of which feature frequently in ME/CFS.

Signs and symptoms

There is a large set of symptoms associated with long COVID, impacting many different organs and body systems. Long COVID symptoms can differ significantly from person to person. Symptom severity ranges from mild to incapacitating.
Common symptoms reported in studies include fatigue, muscle pain, shortness of breath, chest pain, cognitive dysfunction and post-exertional malaise. This symptom worsening typically occurs 12 to 48 hours after activity and can be triggered by either mental or physical effort. It lasts between days and weeks.
Children and adolescents can also experience serious symptoms and long-term adverse health effects, including serious mental health impacts related to persistent COVID19 symptoms. The most common symptoms in children are persistent fever, sore throat, problems with sleep, headaches, shortness of breath, muscle weakness, fatigue, loss of smell or distorted smell, and anxiety. Most children with long COVID experience three or more symptoms.

Neurological symptoms

Common neurological symptoms in long COVID are difficulty concentrating, cognitive impairment and headaches. People also frequently experience loss of taste and loss of smell. Likewise children and young people may also experience cognitive impairment.
Some people with long COVID experience dysautonomia, a malfunction of the autonomic nervous system. People with dysautonomia may experience palpitations and tachycardia after minor effort or upon standing up. This can be associated with dizziness and nausea. If the heart rate is raised by 30 beats per minute or more after continuous standing; this is described as postural orthostatic tachycardia syndrome.
In terms of mental health, people with long COVID often experience sleep difficulties. Depression and anxiety levels are raised in the first two months after infection, but return to normal afterwards. This was in contrast to other neurological symptoms, such as brain fog and seizures, which lasted at least two years. However, among people who were hospitalised for COVID, many have depression and anxiety 2 to 3 years after their infection.

Lungs, heart and digestive system

Difficulty breathing is the second-most common symptom of long COVID, but this subjective symptom does not track with the severity of objective markers of inflammation. Shortness of breath is among the most common symptoms in children and young people as well. People can also experience a persistent cough.
In the cardiovascular system, effort intolerance and chest pain occur often in people with long COVID. Sufferers of Long COVID are also at increased risks of developing strokes, myocarditis, the postural orthostatic tachycardia syndrome, pulmonary embolisms, deep vein thrombosis, and myocardial infarction.
Less frequently, people with long COVID experience diarrhea and nausea.

Reproductive system

In the female reproductive system, long COVID may disrupt fertility, the menstrual cycle, menopause, gonadal function, and ovarian sufficiency. Exacerbation of other long COVID symptoms around menstruation has also been documented.

Other symptoms

and muscle pain are frequently reported as symptoms of long COVID. Some people experience hair loss and skin rashes. People are at increased risk of type1 or type2 diabetes after recovering from acute COVID.

Subgroups

Because the symptom combinations of long COVID vary significantly from person to person, one approach to researching the condition is to define subgroups or clusters of long-haulers. This would allow for more targeted clinical care.

Causes and mechanisms

The causes of long COVID are not understood. It is likely that there is no single cause, but instead multiple, and possibly overlapping, mechanisms that all contribute to the development of long COVID. Organ damage from the acute infection can explain a part of the symptoms, but long COVID is also observed in people where organ damage seems to be absent. Several hypotheses have been put forward explaining long COVID, including:
Further hypotheses include a dysfunction of the mitochondria and the cellular energy system, persistent systemic inflammation, and the persistence of SARS-COV-19 antigens.