Since the onset of the COVID-19 pandemic, there have been reports of people experiencing persistent symptoms weeks to months after initial infection. Early studies in Europe reported persistence of symptoms in 87% of patients discharged from the hospital. However, it has quickly become evident that persistent symptoms after COVID-19 are not restricted to those who were critically ill or hospitalized but can occur in patients who had mild disease and never needed to be hospitalized.

The Centers for Disease Control and Prevention (CDC) calls such cases “post-COVID conditions,” an umbrella term that refers to a range of “new, returning, or ongoing health problems” experienced by people four or more weeks after initial coronavirus infection. Post-COVID conditions also go by several other names, including long COVID, long-haul COVID, chronic COVID, and post-acute COVID-19.

What is long COVID?

Long COVID, or what doctors refer to as post-acute sequelae of COVID-19 (PASC), is a condition marked by the continuation of COVID-19 symptoms—or the emergence of new ones—after recovery from acute (or the initial phase of illness of) COVID-19. While there is not yet a formal definition of long COVID, it generally refers to the persistence of symptoms four weeks or longer after the onset of COVID-19.

Who is at risk for long COVID?

Long COVID can affect anyone, including children, and it can develop in people who had asymptomatic, mild, or severe COVID-19. While it is not yet known why long COVID affects some people and not others, a recent study found that the condition is more common among older people, women, and those who had six or more symptoms during the first week of COVID-19.

Researchers do not yet know the prevalence of long COVID, though the condition is common. A recent study in the U.S. found that approximately one-third of people who had COVID-19 report persistent symptoms up to 9 months after the initial illness.

What causes long COVID?

While the causes of long COVID are not yet known—and research is ongoing—researchers and clinicians have proposed several theories.

• Residual organ damage. This theory holds that the symptoms of long COVID are due to residual damage to organs caused by the body’s own immune response to SARS-CoV-2 infection.
• Remaining virus. This theory suggests that after the immune system eliminates the virus, some remnants of it survive in one or more organs, and it continues to stimulate an immune response.
• Exaggerated Immune response. According to this theory, in some people, COVID-19 sparks an exaggerated immune response; the immune system then remains in an overexcited state, resulting in various symptoms.

Investigations are still underway to better understand long COVID; much research is still necessary.

What are the symptoms of long COVID?

COVID-19 can affect the function of multiple organs in the body, including the lungs, heart, brain, kidneys, and liver. Because of this, long COVID is associated with a broad range of symptoms, including respiratory, neurological, cardiac, and psychological problems, among others.

Symptoms of long COVID may include:

• Fatigue
• Headache
• Shortness of breath
• Chest pain or discomfort
• Cough
• Persistent loss of smell and/or taste
• Joint pain; muscle aches and pain/weakness
• Sore throat
• Memory loss
• Brain fog (difficulty concentrating, sense of confusion or disorientation)
• Dizziness
• Low-grade, intermittent fever
• Rapid or irregular heartbeat (palpitations)
• Anxiety
• Depression
• Post-traumatic stress disorder (PTSD)
• Insomnia
• Earache, hearing loss, and/or ringing in ears (tinnitus)
• Rashes
• Diarrhea, nausea, and/or abdominal pain
• Diminished appetite
• Hair loss

Some people may experience only one of these symptoms, while others may have two or more. Symptoms can vary greatly from one person to the next.

Some of the most commonly reported symptoms include fatigue, shortness of breath, chest pain, loss of smell, and “brain fog,” which is a cognitive state characterized by confusion, difficulty concentrating, and memory problems. These symptoms range from mild to debilitating. Many people report that long COVID symptoms prevent them from returning to work or school, and some with long COVID have difficulties performing everyday chores or even walking short distances.

How is long COVID diagnosed?

There is no single test that can diagnose long COVID. Doctors diagnose it, in large part, based on a patient’s history of COVID-19 and by ruling out other possible causes.

The doctor will ask whether the patient tested positive for COVID-19, when symptoms began, and which symptoms the patient has experienced since the initial infection. The doctor may also ask about underlying medical conditions.

After collecting a medical history, the doctor will conduct a physical exam. The exam will involve routine assessment of blood pressure, heart rate, pulse oximetry, and breathing. Depending on the patient’s symptoms, it may also involve physical, cognitive, and psychological testing. Physical tests may include a 6-minute walking test and/or a test in which the patient must sit on and stand up from a chair five times. Cognitive assessment may involve short tests designed to evaluate memory, language ability, reasoning, and other cognitive skills. With psychological testing, the patient may need to complete a screening questionnaire.

Depending on the patient’s symptoms, the doctor may order specific diagnostic tests. If the patient is experiencing respiratory symptoms, for instance, a chest X-ray may be required. Patients who have cardiac symptoms may need to have an electrocardiogram (known as an ECG or EKG), a painless test that measures heart activity. In some cases, the doctor will order bloodwork.

How is long COVID treated?

For patients who have multiple symptoms, treatment may involve specialists in cardiology, pulmonology, neurology, psychiatry, rehabilitation, and/or other relevant fields of medicine.

Below, by symptom, are treatments and therapies that may help people with long COVID:

• Fatigue. Patients may be taught strategies for “Pacing, Planning, Prioritizing, and Positioning” activities, sometimes known as the “4 Ps.” They may also be advised to undertake a physical exercise program that involves stretching, strengthening, and aerobic activities. If exercise worsens symptoms, the patient should stop or reduce the intensity and/or duration of the activity.
• Respiratory symptoms. Treatment may involve breathing exercises, use of supplemental oxygen, and pulmonary rehabilitation, a medically guided program in which patients perform exercises and learn breathing techniques. Patients may need to use a pulse oximeter to monitor blood oxygen saturation levels. (If blood oxygen saturation levels fall below 92%, they should seek medical attention.) If respiratory symptoms do not improve, patients may be referred to a pulmonologist.
• Cardiac symptoms. Patients with cardiac symptoms may be referred to a cardiovascular specialist for cardiac symptoms, such as rapid heart rate or chest pain. Treatment may involve cardiac rehabilitation. Medications may also be used to control specific symptoms.
• Neurological symptoms. If patients have cognitive symptoms such as memory loss and/or brain fog, doctors may recommend exercise and to remain physically active. For patients with memory impairment, treatment might involve memory exercises and the use of memory aids such as calendars and planners. Patients may be referred to a neurologist.
• Psychological symptoms. Treatment commonly involves counseling, support groups, and medications to manage depression, anxiety, or other conditions.
• Smell and taste symptoms. Patients who have reduced or lost sense of smell and/or taste, doctors may prescribe topical (drops or sprays) corticosteroids to reduce inflammation in the nose. They may also perform olfactory training, a therapy in which patients regularly sniff various odors for a set period (usually several weeks) with the aim of restoring sense of smell. If symptoms do not resolve, patients may be referred to an ear, nose, and throat (ENT) specialist.

Patients who have symptoms related to kidney, liver, or endocrine function—as well as those related to dermatology and gastrointestinal issues, treatment are usually referred to the appropriate specialist.

What is the outlook for people with long COVID?

For some long-haulers, the symptoms of long COVID resolve on their own within three months after onset of their initial COVID-19 illness. For others, however, symptoms can continue well beyond three months.

Treatments and therapies for symptoms of long COVID can improve quality of life and help people gradually rehabilitate. What’s more, in the first months of 2021, many people with long COVID reported that their symptoms diminished or even disappeared upon receiving a COVID-19 vaccine. More research is needed to understand how widespread this unanticipated—but positive—outcome is and why vaccination appears to help some with long COVID recover.