Long COVID symptoms, testing and the research on treatment

The National Academies of Sciences, Engineering, and Medicine published a consensus definition in 2024: long COVID is an infection-associated chronic condition that occurs after SARS-CoV-2 infection and is present for at least three months as a continuous, relapsing and remitting, or progressive disease state that affects one or more organ systems (NASEM, 2024).

The CDC lists the symptoms people report most: tiredness or fatigue that interferes with daily life, symptoms that get worse after physical or mental effort, difficulty thinking or concentrating (brain fog), cough, shortness of breath and heart palpitations (CDC). Symptoms can come and go, and a good week can follow a bad one.

The same definition names diagnosable conditions that can make up long COVID, among them postural orthostatic tachycardia syndrome (POTS), ME/CFS, arrhythmias, interstitial lung disease, diabetes and autoimmune disorders (NASEM, 2024). Worsening after effort has its own name, post-exertional malaise. For a closer look at how clinicians reach the diagnosis, read how you know if you have long COVID.

Researchers study several explanations, and in one person more than one may apply. No study has shown a single mechanism that accounts for every case. The main lines of evidence:

• Immune differences. A 2023 Nature study profiled the immune systems of 275 people and found features that separated long COVID from recovery at the group level, including lower cortisol and higher antibody responses to Epstein-Barr virus antigens (Klein et al., 2023). A 2025 paper in Nature Immunology examined soluble immune biomarkers associated with long COVID across large patient groups (Nature Immunology, 2025).
• Viral material that persists. A research assay found SARS-CoV-2 spike protein in the plasma of 60% of 37 people with post-acute sequelae at some point 2 to 12 months after infection, and in none of 26 people who recovered (Swank et al., 2023). A larger 2024 study found more viral antigen in the blood of people who had been infected than in uninfected people for up to 14 months (Peluso et al., 2024).
• Reactivated latent viruses. In 280 adults after SARS-CoV-2 infection, researchers linked antibody evidence of recent Epstein-Barr virus reactivation to long COVID with fatigue (Peluso et al., 2023).
• Interferon signalling. The antiviral interferon response is a further focus; our piece on the type I interferon signature after a virus walks through it.

Each finding describes a group, and each leaves open questions about cause and direction. The inflammation biology of long COVID covers the immune evidence in more depth.

No. The CDC states that there is no approved laboratory test that can determine whether symptoms or conditions are due to long COVID. Its clinical guidance adds that no laboratory test can diagnose or rule out long COVID with certainty, and that a positive SARS-CoV-2 test is not required for the diagnosis. Clinicians diagnose it from the history, the timeline of symptoms after infection and an examination.

Standard tests serve a different purpose: they look for other conditions that could explain the symptoms. The CDC notes that routine blood tests, chest X-rays and ECGs may be normal in someone with long COVID (CDC), and a large study found common lab tests unreliable for diagnosing it (CU Anschutz). Antibody tests answer another question. A spike antibody result can reflect past infection or vaccination, and laboratories use nucleocapsid antibody tests to look for past infection in vaccinated people (CDC). Neither result diagnoses long COVID.

Our article on whether there is a blood test for long COVID covers what exists in 2026.

Research panels measure many immune proteins at once. Markers that recur in the long COVID literature include IL-6, TNF-α, IFN-γ and the interferon-induced chemokine IP-10 (Klein et al., 2023; Nature Immunology, 2025). A panel places each against a healthy reference, and a retest shows which way each moves over months. You and your doctor can read that series beside your symptom history.

The limits matter as much. A research panel cannot diagnose long COVID, separate it from other conditions in one person, predict how your illness will go or choose a treatment. A difference between groups in a study is no verdict about one person.

Mune Mirror™^* is currently in development, and the performance characteristics of this test have not yet been established. It is investigational. It does not diagnose, detect, screen for, treat, cure or prevent any disease. Results are for research and informational purposes, to discuss with your own doctor.

For someone living with long COVID who wants objective data, the Mune Mirror™ Baseline Study is the next step. It measures 50 people with long COVID and 300 healthy participants, starts on 15 October 2026, includes up to three at-home blood draws and returns each participant's own results. Sign-up is an application and does not guarantee a place. Read about the Baseline Study.

The CDC states that there are no approved treatments for long COVID. Its clinical guidance describes care tailored to each person's symptoms and conditions (CDC). Decisions about treatment belong with your doctor.

Research is active. The NIH-funded RECOVER program combines observational studies that follow people over time with clinical trials that test interventions across long COVID presentations, including fatigue, cognitive symptoms, sleep problems and autonomic dysfunction. The candidates under study change as trials open and close; our article on long COVID treatments being researched in 2026 tracks them.

People who try something want to know whether it made a difference. Our pieces on telling whether a change is helping and measuring a treatment's effect over time explain why a baseline and retests help that question, and the guide to unwellness testing explains the approach.

Mune Mirror™ measures more than 1,000 immune and inflammation proteins from an at-home sample, including markers that recur in long COVID research, and benchmarks each against a healthy reference. Repeated over time, it gives you and your doctor a measured record beside your symptoms. It does not diagnose long COVID.

Is there a test for long COVID?

No approved laboratory test can determine whether symptoms are due to long COVID, according to the CDC, and routine blood tests may be normal. Clinicians diagnose it from the history and an examination. Research panels measure immune proteins that differ between groups with and without long COVID, and the Mune Mirror™ Baseline Study measures people with long COVID beside healthy participants from 15 October 2026.

What are the most common long COVID symptoms?

The CDC lists tiredness or fatigue that interferes with daily life, symptoms that get worse after physical or mental effort, difficulty thinking or concentrating (brain fog), cough, shortness of breath and heart palpitations. Symptoms can come and go.

Can a blood test show long COVID?

No blood test diagnoses long COVID. Standard tests look for other conditions and may be normal. Research panels find immune differences between groups of people, and those differences do not diagnose one person. Research-grade panels such as Mune Mirror™ are investigational and for research and informational use.

Are there approved treatments for long COVID?

The CDC states that there are no approved treatments for long COVID, and doctors tailor care to each person's symptoms and conditions. NIH's RECOVER program runs clinical trials across fatigue, cognitive symptoms, sleep problems and autonomic dysfunction. Talk with your doctor about any treatment decision.

How long does long COVID last?

By the 2024 National Academies definition, long COVID is present for at least three months and can be continuous, relapsing and remitting, or progressive. The course differs from person to person.