MIS-A in Adults: Symptoms, Diagnosis and Treatment

MIS-A stands for Multisystem Inflammatory Syndrome in Adults. CDC describes multisystem inflammatory syndrome as a rare but serious condition associated with SARS-CoV-2, the virus that causes COVID-19. Several organs and body systems can be affected, including the heart, lungs, kidneys, brain, skin, eyes and gastrointestinal tract.¹

The syndrome can affect children, where it is called MIS-C, and adults, where it is called MIS-A. Both are rare, and MIS-C has been reported more often than MIS-A.¹

MIS-A is not the same as ordinary post-viral symptoms or Long COVID. It is an acute inflammatory syndrome that generally requires hospital assessment.

It usually develops in the weeks after infection rather than during it. CDC describes the main risk factor as being infected with SARS-CoV-2 in the previous two to six weeks.¹

The earlier infection may have been mild or barely noticed. Among children with MIS-C, many had no or few COVID-19 symptoms,¹ and in the first published adult case series antibody testing was needed to identify prior infection in roughly a third of the 27 patients described.⁶ A remembered positive test is not a requirement for MIS-A to be considered.

What clinicians look for is a combination: fever, laboratory evidence of systemic inflammation, and new involvement of several organ systems, in the absence of a more likely alternative diagnosis.³

Severe cardiac illness — including myocarditis, pericarditis and new ventricular dysfunction — sits at the centre of the adult definition, alongside shock, gastrointestinal symptoms and skin and eye involvement.³ A systematic review of 221 reported adult patients found hyperinflammation with multiorgan involvement largely outside the lungs, and noted how difficult MIS-A can be to distinguish from a biphasic course of acute COVID-19 or from post-acute sequelae of infection.⁵

The underlying mechanisms continue to be studied. A dysregulated immune response following infection is the leading explanation, but MIS-A is not established as having one simple cause, and no genetic explanation has been established.

Reported case numbers should also be read with care: reporting to CDC is voluntary, adult cases are fewer than paediatric ones, and this page does not claim that cases are rising or falling.

MIS-A is identified in hospital. There is no single test for it. Clinicians build a picture from the person’s medical history, evidence of recent or current SARS-CoV-2 infection, fever, physical examination, blood tests showing systemic inflammation, assessment of which organs are involved, cardiac testing where indicated, and the exclusion of a more likely alternative diagnosis such as bacterial sepsis or a flare of an existing condition.³ Because features overlap with several other serious illnesses, testing for alternative diagnoses is directed by the person’s own signs and symptoms.⁴

CDC also publishes a surveillance case definition for MIS-A. Its purpose is to help identify and report cases consistently across the United States. It is a public-health reporting tool, not a substitute for clinical judgement, and not something a reader can apply to themselves.

In summary, the current CDC definition covers a person aged 21 or older who has been hospitalised for at least 24 hours — or whose illness resulted in death — with fever, no more likely alternative diagnosis, specified clinical criteria of which at least one must be a primary criterion, laboratory evidence of SARS-CoV-2 infection, and elevated markers of systemic inflammation.³ The detail sits below for reference.

CDC surveillance case definition

Summarised from CDC’s MIS case definitions and reporting page, last updated 19 February 2026. Surveillance criteria support identification and reporting of cases. They are not a diagnostic checklist for readers, and meeting or not meeting them does not establish whether a person has MIS-A.³

Entry criteria

• A person aged 21 years or older
• Hospitalisation for at least 24 hours, or hospitalisation of any length with an illness resulting in death
• Subjective or documented fever of 38.0°C or higher for at least 24 hours before hospitalisation, or within the first three days of hospitalisation

Clinical criteria

• No alternative diagnosis, such as bacterial sepsis or an exacerbation of a chronic medical condition
• At least three of the clinical criteria below, occurring before hospitalisation or within the first three days of hospitalisation, of which at least one must be a primary criterion

Primary clinical criteria

• Severe cardiac illness — including myocarditis, pericarditis, coronary artery dilatation or aneurysm, new-onset right or left ventricular dysfunction, second- or third-degree AV block, or ventricular tachycardia. Cardiac arrest alone does not meet this criterion.
• Rash and non-purulent conjunctivitis

Secondary clinical criteria

• New-onset neurological signs and symptoms, including encephalopathy in a person without prior cognitive impairment, seizures, meningeal signs, or peripheral neuropathy including Guillain–Barré syndrome
• Shock or hypotension not attributable to medical therapy
• Abdominal pain, vomiting or diarrhoea
• Thrombocytopenia — a platelet count below 150,000/μL

Laboratory criteria

• Evidence of SARS-CoV-2 infection by a positive nucleic acid amplification, serology or antigen test
• Evidence of systemic inflammation — elevated levels of at least two of C-reactive protein, ferritin, interleukin-6, erythrocyte sedimentation rate or procalcitonin

Discharge is a milestone, not an ending. After a serious illness or a hospital admission, people often describe a second phase that no one prepared them for — one that is less about acute physiology and more about stamina, confidence and trust.

Not everyone experiences this, and none of it is universal to MIS-A. But among the things people describe after a frightening acute illness are:

• Fatigue or reduced stamina
• Anxiety about symptoms returning
• Increased monitoring of heart rate, breathing or physical sensations
• Uncertainty about how much activity is safe
• Reduced confidence in the body
• Difficulty returning to work or ordinary routines
• Distress after hospitalisation
• Frustration with an uncertain recovery timeline

Persistent or new physical symptoms need medical follow-up. They must not be attributed to stress or nervous-system patterns by default — including by you. Chest pain, breathlessness, palpitations, fainting, fever or anything new, severe or worsening is a reason to contact your clinical team, not a reason to practise harder.

Longer-term outcomes in adults remain insufficiently characterised. CDC states plainly that fewer adults with MIS have been reported and that longer-term complications in adult populations have not been well characterised.⁴ This page therefore does not tell you how likely a full recovery is, how long recovery takes, or what proportion of adults are left with lasting effects — because a current, suitable source for those statements in adults does not exist.

What follow-up looks like depends on which organs were involved and on how the illness went. CDC guidance written for children states that evaluation and testing after hospitalisation are based on each patient’s presentation and clinical course, that cardiology follow-up with repeat echocardiogram is generally recommended where there were cardiac manifestations, that exercise and strenuous activity are generally limited until a cardiologist gives clearance, and that follow-up with a primary care provider matters.⁴ That is paediatric guidance; adult follow-up is decided case by case by the treating team.

Depending on the individual, follow-up may involve primary-care review, cardiology follow-up, repeat blood tests, an electrocardiogram or cardiac imaging, review of medication, advice about returning to activity, and rehabilitation or other specialist input. There is no universal schedule, and nothing on this page should be used to decide what your own follow-up ought to include.

If symptoms continue after MIS-A, that does not automatically mean Long COVID. They are different things, and continuing symptoms deserve assessment on their own terms rather than a label applied by default.⁹

Because MIS follows SARS-CoV-2 infection, reducing the likelihood of infection is the route to reducing risk. CDC states that, based on current knowledge, the best way to prevent MIS-C or MIS-A is to take action to protect yourself from getting infected with SARS-CoV-2, including getting an updated COVID-19 vaccination.¹⁸

In practice that means staying up to date with COVID-19 vaccination where it is recommended for you, following current local public-health advice, and using the everyday measures set out in current respiratory-virus guidance — improving ventilation, and limiting close contact when someone is acutely infectious, where that is practical.⁷⁸

Recommendations change. This page does not reproduce pandemic-era checklists as fixed universal rules, and it does not give personalised advice — including on hand hygiene products, which are not a substitute for the measures above and do not address a virus in the way antibacterial marketing implies.

Someone who has had MIS-A should discuss vaccination timing with their clinical team and follow current local guidance. CDC’s guidance on MIS notes that a conversation between the patient, their family and the clinical team or a specialist should take place to assist with decisions about COVID-19 vaccination after MIS.⁴

On timing specifically, CDC’s interim clinical considerations — which are United States guidance — treat a history of MIS-C or MIS-A as a precaution rather than a barrier. Experts consider the benefits of COVID-19 vaccination to outweigh the theoretical risks for people who meet two recovery criteria: clinical recovery has been achieved, including return to baseline cardiac function; and it has been at least 90 days since the MIS-A diagnosis. Vaccination may also be considered for people who do not meet both criteria, at the discretion of their clinical care team.¹²

Readers outside the United States should follow their own national guidance. This page cannot tell you when to be vaccinated.