The Post-traumatic Stress Disorder Checklist for The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, DSM-5 (PCL-5) is a 20-item self-report measure that assesses the 20 DSM-5 symptoms of PTSD.

The study partipicipant answer first a brief Criterion A för PTSD. If the answer is affirmative (i.e. PTSD is suspected) the participants continue with 20 questions (items). Each item is rated from 0 ("not at all") to 4 ("extremely") to indicate the degree to which they have been bothered by that particular symptom over the past month. Ratings can be added to form an overall score (from 0 to 80) and the higher score means a worse outcome.

Th Perceived Stress Scale (PSS-14) is a self-reported measure which assesses the degree to which the respondent has perceived situations in his/her life within the past month as stressful.

The PSS-14 is comprised of 14 items intended to measure how unpredictable, uncontrollable, and overloaded individuals find their life circumstances. Individuals rate items on a 5-point Likert scale, ranging from 0 - "Never" to 4 - "Very often." Scores range from 0-56, with higher scores indicating greater perceived stress.

The cognitive Failures Questionnaire (CFQ) is a self-report questionnaire consisting of 25 items assessing deficits regarding attention, perception, memory and motor functioning in everyday life. The total CFQ score is calculated by summation of all answers and scores range from 0-100. A higher total score indicates more subjective cognitive failure.

Self-assessment questionnaire.

Study participant report grade of eventual sick-leave. According to Swedish legislation, four degrees of sick leave are possible (25%, 50%, 75%, 100%), where a higher number of percentages means worse outcome i.e. more reduced ability to work.

They also report the time of incapacity for work (number of months of sick leave (1- 100)) where higher numbers mean worse outcome i.e. longer time of incapacity for work

Body mass index (BMI) gives an indication of the body size. Along with several other factors, BMI can help estimate the risk of a cardiovascular disease.

BMI is calculated using weight and height. BMI Categories: Underweight = <18.5, Normal weight = 18.5-24.9, overweight = 25-29.9, obesity = BMI of 30 or greater. The values under 18.5 and over 25 indicate worse outcome.

The waist measurement is an indicator of the abdominal obesity that is associated with an increased risk of type 2 diabetes, cardiovascular disease and death, The values over 94cm for men and over 80cm for women indicate worse outcome i.e. abdominal obesity.

PEF rate is the volume of air forcefully expelled from the lungs in one quick exhalation, and is an indicator of ventilation adequacy as well as airflow obstruction. Air flow is measured with the portable, hand-held device. Three readingss are performed ond the highest of three readings is used as the recorded value of the PEF Rate. PEF is measured in units of liters per minute (0-800). The expected value depends on the participant's sex, age, and height but higher numbers in the given study participant mean better outcome i.e. better lung function.

60 Second Sit-to-Stand Test (60STS) gives a measure of exercise capacity. The participant is encouraged to complete as many full stands as possible within 60 seconds. The number of full stands is registered (0-100) where higher numbers mean better outcome i.e. better physical fitness.

Beta-amyloid 40 and 42 are formed from amyloid precursor protein (APP) and are normally transported to the cerebrospinal fluid (CSF). In Alzheimer's disease, Beta-amyloid 42 accumulates in senile plaque and thus the level falls in CSF. Slightly lower levels of beta-amyloid 42 can also be seen in other dementia diseases.

Cerebrospinal fluid will be collected by trained physician and results will be reported as ng/L. The expected value depends on the participant's age, but lower values in the given study participant mean worse outcome i.e. more possible neurodegeneration.

Beta amyloid 40 is the most common variant of beta amyloid in CSF, while beta amyloid 42 predominates in senile plaques . Decreased ratio of Beta amyloid 42/40 is a strong marker of Alzheimer's disease and can be detected early in the disease progression, even before clinical dementia occurs.

Cerebrospinal fluid will be collected by trained physician and the result is reported as a ratio. Reference interval: > 0.72 ( > 50 years of age). Lower ratio means worse outcome i.e. possible Alzheimer's disease.

Neurogranin is a protein expressed in synapses of the pyramidal cells of the hippocampus and cortex. Neurogranin is elevated in cerebrospinal fluid from individuals with Alzheimer's disease, but not from healthy individuals or individuals with other neurodegenerative diseases.

Cerebrospinal fluid will be collected by trained physician and results will be reported as ng/L. The expected value depends on the participant's age, but higher values in the given study participant mean worse outcome i.e. more possible neurodegeneration.

Tau protein is a recognized biomarker of cortical damage and is assumed to be a nonspecific marker of neurodegeneration.

Cerebrospinal fluid will be collected by trained physician and results will be reported as ng/L. The expected value depends on the participant's age, but higher values in the given study participant mean worse outcome i.e. more possible cortical damage/neurodegeneration.

Under physiological conditions, tau protein regulates the assembly and maintenance of the structural stability of microtubules in nerve cells. In certain brain diseases tau proteine becomes abnormally hyperphosphorylated, which ultimately causes the microtubules to disassemble, and the free tau molecules aggregate into paired helical filaments.

Phosphorylated tau (P-tau) is assumed to be a relatively specific marker for Alzheimers disease because neurofibrillary tangles that är found in AD patients primarily consist of tau protein in the abnormally hyperphosphorylated state

Cerebrospinal fluid will be collected by trained physician and results will be reported as ng/L. The expected value depends on the participant's age, but higher values in the given study participant mean worse outcome i.e. more possible neurodegeneration.

Neurofilament light (NFL) is a recognized biomarker of subcortical large-caliber axonal degeneration and is assumed to be a nonspecific marker of neurodegeneration.

Cerebrospinal fluid will be collected by trained physician and results will be reported as ng/L. The expected value depends on the participant's age, but higher values in the given study participant mean worse outcome i.e. more possible neurodegeneration.

Blood-based biomarkers of neurodegeneration have obvious advantages over both CSF and neuroimaging biomarkers. The collection of blood is inexpensive, noninvasive, and a more feasible measure for use in the general population, especially if serial collection is needed. Neurofilament light (NFL) is a recognized biomarker of subcortical large-caliber axonal degeneration and is assumed to be a nonspecific marker of neurodegeneration.

Plasma will be collected by trained personnel and results will be reported as ng/L. The expected value depends on the participant's age, but higher values in the given study participant mean worse outcome i.e. more possible neurodegeneration. The values will be also compared with NFL values in cerebrospinal fluid (outcome 20), which are still the "golden standard" of NFL measurement

The human APOE gene exists as three polymorphic alleles-ε2, ε3 and ε4-which have a worldwide frequency of 8.4%, 77.9% and 13.7%, respectively. However, the frequency of the ε4 allele is dramatically increased to ~40% in patients with late onset Alzheimers disease. APOE4 allele has also been correlated with severe COVID-19 outcomes.

Plasma will be collected by trained personnel and results will be reported as combination of two alleles with six possible alternatives: 2/2, 2/3, 2/4, 3/3, 3/4, 4/4. Alternatives with the APOE4 allele indicate worse outcomes and combinationen: 4/4 indicates the worst possible outcome.

Imaging of the brain using Magnetic Resonance Imaging (MRI) scans. The scans are compared over time to assess changes of brain volume and progress/regression of signal abnormalities/lesions in gray and white matter

Imaging of the brain activity at rest using resting-state functional Magnetic Resonance Imaging (rs-fMRI). Rs-fMRI measures spontaneous low-frequency fluctuations in the BOLD signal to investigate the functional architecture of the brain and to identify various resting-state networks (RSN). The scans are compared over time to detect changes in functional and structural connectivity of the brain.

The gut microbiome in COVID-19 is characterized by increased fecal fungal load and increased beta-diversity (more heterogeneous), and it is unstable over time and also persistently altered after disease resolution. Assessment of gut microbiome as well as changes over time will be carried out via analysis of the fecal samples for microbial composition using 16S microbiome analysis, metabolomics and Next Generation Sequencing.