among viral test–negative children, that is there was an incidence proportion difference of only 3.7%. long covid was identified more in those cared for intensive care unit during the acute illness phase, children younger than 5 years, and those with complex chronic conditions. neurological symptoms, such as headache, vertigo, and paresthesiae were not significant findings in this study, as opposed to in adults. a 2021 study from the uk office for national statistics with 20,000 participants, including children and adults, found that, in children who tested positive, at least one symptom persisted after five weeks in 9.8% of children aged two to eleven years and in 13% of children aged 12 to 16 years. a 2022 university college london study in the uk found that children ages 11–17 who had a positive pcr test were more likely to have three or more symptoms three months after their diagnosis compared to those with a negative test. causes it is currently unknown why most people recover fully within two to three weeks and others experience symptoms for weeks or months longer. the exact processes that cause long covid remain uncertain, but research has established that long covid is associated with changes in fatty acid metabolism and mitochondrial dysfunction. a march 2021 review article cited the following pathophysiological processes as the predominant causes of long covid: direct toxicity in virus-infected tissue, especially the lungs ongoing inflammation due to post-infection immune system dysregulation vascular injury and ischemia caused by virus-induced hypercoagulability (tendency to form internal clots) and thromboses (internal blood clots) impaired regulation of the renin-angiotensin system related to the effect of sars-cov-2 on ace2-containing tissue in october 2020, a review by the united kingdom's national institute for health and care research hypothesized that ongoing long covid symptoms may be due to four syndromes: permanent damage to the lungs and heart, post-intensive care syndrome, post-viral fatigue, sometimes regarded as the same as myalgic encephalomyelitis / chronic fatigue syndrome (me/cfs) continuing covid-19 symptoms, and damage to the blood which deprives the body of oxygen. other situations that might cause new and ongoing symptoms to include: the virus being present for a longer time than usual, due to an ineffective immune response; reinfection (e.g., with another strain of the virus); damage caused by inflammation and a strong immune response to the infection; post-traumatic stress or other mental sequelae, especially in people who had previously experienced anxiety, depression, insomnia, or other mental health difficulties; inhibited oxygen exchange as a result of persistent circulating blood plasma microclots; and development of various autoantibodies after infection. similarities to other syndromes long covid is similar to post-ebola syndrome and the post-infection syndromes seen in chikungunya and myalgic encephalomyelitis/chronic fatigue syndrome (me/cfs), which is often triggered by infection and immune activation and was previously also known as "post-viral fatigue". the pathophysiology of long covid may be similar to these other conditions. some long covid patients in canada have been diagnosed with me/cfs, a "debilitating, multi-system neurological disease that is believed to be triggered by an infectious illness in the majority of cases". there is need for more research into me/cfs; anthony fauci, former chief medical adviser to the us government, said that covid-19 is a "well-identified etiologic agent that should be very helpful now in getting us to be able to understand ". risk factors several risk factors have been found for long covid: gender – women are more likely to develop long covid than men. some research suggests this is due primarily to hormonal differences, while other research points to other factors, including chromosomal genetics, sex-dependent differences in immune system behavior; non-biological factors may also be relevant. age, with older people more at risk obesity asthma depression or anxiety post-traumatic stress the number of symptoms during acute covid diagnosis there are no standardized tests or biomarkers to determine if symptoms existing weeks to years after covid-19 infection are defined within one condition called long covid. post-covid conditions are not one illness, but rather may involve numerous organ systems and disorders. in preliminary research, a custom-designed, mass spectrometry assay on blood samples assessing 96 proteins in inflammatory responses showed signs of inflammation remaining up to 40-60 days after covid infection. risk reduction a 2022 study found that covid-19 vaccination reduced long covid risk by about 15%. as of 2022, there are no firm definitions about how long covid occurs, no precise biomarkers or imaging tests to confirm it, no knowledge of its mechanism, and no therapies for treating long covid. treatment and management as of 2022, there are no established pharmaceutical treatments for long covid, although numerous clinical trials are in progress to establish the efficacy and safety of possible therapies. management of long covid depends on symptoms, with current guidelines recommending multidisciplinary rehabilitation to improve symptoms and quality of life. rest, planning and prioritising are advised for people with fatigue. people who suffer from post-exertional symptom exacarbation may benefit from activity management with pacing. people with allergic-type symptoms such as rashes on the skin may benefit from antihistamines. people should also be routinely screened for mental health conditions, such as post-traumatic stress, which has been associated with fatigue severity. olfactory dysfunction symptoms from a covid infection can be persistent and be impactful on a person's life. approaches for treating persistent olfactory dysfunction include medications such as systematic corticosteroids and intranasal corticosteroids, palmitoylethanolamide and luteolin, however the effectiveness of these approaches is not clear. it is also not clear if medications or olfactory training techniques are effective at preventing a person from developing longer term or persistent olfactory dysfunction after a covid infection. health system responses australia in october 2020, a guide published by the royal australian college of general practitioners (racgp) says that ongoing post-covid-19 infection symptoms such as fatigue, shortness of breath and chest pain will require management by gps, in addition to the more severe conditions already documented. in december 2021, research by a health economics expert at deakin university suggests that even without fully understanding the omicron variant's effects yet, a further 10,000 to 133,000 long covid cases are likely to emerge on top of the current approximately 9450 in new south wales and 19,800 in victoria, after border and other restrictions had been recently lifted. the racgp released new guidelines for general practitioners to manage a large number of new long covid patients. south africa in october 2020, the datcov hospital surveillance department of the national institute for communicable diseases (nicd) looked into a partnership with the international severe acute respiratory and emerging infection consortium (isaric) (an open-access research and data resource) in order to conduct clinical research into the impact pasc may have within the south african context. as of 30 january 2021, the project has yet to receive ethical approval for the commencement of data collection. ethics approval was granted on 3 february 2021 and formal data collection began on 8 february 2021. united kingdom in britain, the national health service set up specialist clinics for the treatment of long covid. the four chief medical officers of the uk were warned of academic concern over long covid on 21 september 2020 in a letter written by trisha greenhalgh published in the bmj signed by academics including david hunter, martin mckee, susan michie, melinda mills, christina pagel, stephen reicher, gabriel scally, devi sridhar, charles tannock, yee whye teh, and harry burns, former cmo for scotland. in october 2020, nhs england's head simon stevens announced the nhs had committed £10 million to be spent that year on setting up long covid clinics to assess patients' physical, cognitive, and psychological conditions and to provide specialist treatment. future clinical guidelines were announced, with further research on 10,000 patients planned and a designated task-force to be set up, along with an online rehabilitation service – "your covid recovery". the clinics include a variety of medical professionals and therapists, with the aim of providing "joined-up care for physical and mental health". nhs long covid clinics have been found to positively impact quality of life and support the management of symptoms, although further research is required to improve these services. the national institute for health research has allocated funding for research into the mechanisms behind symptoms of long covid. in december 2020, university college london hospitals (uclh) opened a second long covid clinic at the national hospital for neurology and neurosurgery for patients with post-covid neurological issues. the first clinic had opened in may, primarily focused on respiratory problems, but both clinics refer patients to other specialists where needed, including cardiologists, physiotherapists and psychiatrists. by march 2021 there were 69 long covid clinics in the english nhs, mostly focussing on assessing patients, with more planned to open. there were fears that community rehabilitation services did not have capacity to manage large numbers of referrals. on 18 december 2020, the national institute for health and care excellence (nice), the royal college of general practitioners (rcgp) and the scottish intercollegiate guidelines network (sign) published a guide to the management of long covid. the guideline was reviewed by representatives of the uk doctors #longcovid group, an online support group for covid long-haulers, who said that it could be improved by introducing a more comprehensive description of the clinical features and physical nature of long covid, among other changes. in november 2021 complaints were reported from nhs staff that neither their employers nor their trades unions were supportive, though the british medical association was pushing for long covid to be classed as an occupational disease. in may 2022 demand for occupational therapy led rehabilitation services in britain was reported to have increased by 82% over the previous six months as occupational therapists were supporting people whose needs have become more complex because of delays in treatment brought about by the pandemic. half of occupational therapists surveyed were supporting people affected by lasting covid symptoms. united states on 23 february 2021, the national institutes of health director, francis collins, announced a major initiative, backed by $1.15 billion in funding over 4 years, to identify the causes and ultimately the means of prevention and treatment of people who have long covid. the initiative took on the name the "researching covid to enhance recovery," or recover. the initiative intends to fund studies at more than 200 research sites across the united states. part of this initiative includes the creation of the covid-19 project, which will gather data on neurological symptoms. in february 2022, at least sixty-six hospitals and health systems had launched covid recovery programs to aid patients who experience long term or lingering symptoms. societal impact and support communities as of 2022, several countries and medical organizations have produced guidelines on long covid for clinicians and the public. people with long covid may need care within several clinical disciplines for long-term monitoring or intervention of ongoing symptoms, and to implement social services, physical therapy, or mental health care. in some countries, such as the uk and germany, specialized long covid outpatient clinics have been established to assess individual cases for the extent of surveillance and treatment needed. two reviews indicated that primary physicians should provide the first assessment of people with long covid symptoms, leading to specialist referrals for more complex long covid symptoms. long-term follow-up of people with long covid involves outcome reports from the people themselves to assess the impact on their quality of life, especially for those who were not hospitalized and receiving regular clinical follow-up. digital technologies, such as videoconferencing, are being implemented between primary care physicians and people with long covid as part of long-term monitoring. some people experiencing long covid have formed community care networks and support groups on social media websites. internationally, there are several long covid advocacy groups. clinical advice on self-management and online healthcare programs are used to support people with long covid.