The MLC-R aims to create a large-scale registry that provides data on epidemiology, phenotypes, and disease trajectories of and health care for Long COVID at any age in Germany, which can be used for future clinical trials.

Infections with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been observed in Germany since January 2020 and can result in acute coronavirus disease 2019 (COVID-19) as well as in long-term sequela, referred to as Long COVID. The umbrella term Long COVID comprises ongoing new SARS-CoV-2-associated symptoms later than four weeks from the onset of acute COVID-19. The term Post-COVID-Condition (PCC) was introduced by the WHO and stands for ongoing or new SARS-CoV-2-associated symptoms, which persisted for at least two months. These symptoms often include fatigue, brain fog, dyspnea, orthostatic intolerance, as well as exercise intolerance, with a worsening of symptoms after mild daily activities (post-exertional malaise, PEM). PCC can severely impair daily function, social participation, and health-related quality of life. The prevalence was estimated as up to 15% in infected people with pre-Omicron variants and lower with Omicron variants. Risk factors include female gender and pre-existing morbidity, with low risk in young children. The most severe form of PCC in people with initially mild or moderate COVID-19 is myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The prevalence of ME/CFS was shown to increase in the context of the pandemic. While progress has been made in deciphering the pathogenesis of acute COVID-19, the mechanisms of Long COVID/PCC are poorly understood. Increasing evidence indicates that remaining viral particles, as well as inflammation, altered microcirculation, dysfunction of the autonomic nervous system, and/or autoimmunity, may contribute.

With the web-based German MLC-R, we aim at deep phenotyping of PCC, identification of subtypes and risk factors, describing trajectories of the disease and patient journeys, and providing clinical data for future clinical trials. Patients are also invited to contribute biosamples for future translational research.

Inclusion Criteria:

I. Written informed consent of the patient or legal guardian.

II. Confirmed SARS-CoV-2 vaccination and/or confirmed or probable SARS-CoV-2 infection: Positive SARS-CoV-2 polymerase chain reaction (PCR) or rapid antigen test (AST), documented probable COVID-19 (e.g., typical CT scan), probable COVID-19 with a history of high-risk contact, anti-SARS-CoV-2-N antibodies (and/or in non-vaccinated people -S-IgG antibodies) following probable COVID-19.

III. Additional ICD-10 codes: U09.9!V: Suspected post-COVID-19 condition, unspecified; U12.9!V: suspected adverse reactions to COVID-19 vaccine use, unspecified (post-COVIDvac condition).

Exclusion Criteria:

• Any subsequent medical data that question the diagnosis of PCC or post-COVIDvac condition
• Clinical picture can be explained by another underlying disease.
• Pregnancy

Patients with PCC