Although the greatest impact of COVID-19 has undeniably fallen upon the elderly, and among younger cohorts with preexisting comorbidities, we've seen numerous - albeit, mostly anecdotal - reports of prolonged illness and slow recoveries even among healthy young adults.
While the public has focused primarily on the death toll, there remains much we don't know about the long-term sequelae of SARS-COV-2 infection among survivors.
Those sick enough to be hospitalized have been the most studied, and many have documented long-term health deficits linked to infection. A few studies include:
JASN: Acute Kidney Injury In Hospitalized Patients With COVID-19
JAMA: Two Studies Linking SARS-CoV-2 Infection To Cardiac Injury
The Lancet: Yet Another Study On Neurological Manifestations In Severe COVID-19 Patients
Over the past few months, we've seen cardiologists and neurologists weigh in on the potential for seeing huge increases in COVID-19 related heart failure and neurological diseases, some that may not become fully apparent for years.
Clyde W. Yancy, MD, MSc1,2; Gregg C. Fonarow, MD3,4JAMA Cardiol. Published online July 27, 2020. doi:10.1001/jamacardio.2020.3575
Emily A. Troyer, Jordan N. Kohn, and Suzi Hong
And last July Dr. Anthony Fauci expressed concerns that many COVID patients are suffering from a post-viral syndrome - similar to ME/CFS - which has disabled and traumatized well over a million Americans over the past 3 decades (see NIH About CFS/ME).
While there remains much we don't know about the size and scope of the problem, four weeks ago in PAHO Epi Alert: Complications & Sequelae Of COVID-19, we looked at a 16-page PAHO (Pan American Health Organization) Epidemiological Alert on Complications and sequelae of COVID-19.
Despite recent media reports of lingering illness (including myocarditis) among some college athletes, relatively little is known about the long-term health impacts of mild or moderate SARS-CoV-2 infection on young, healthy adults.
Yesterday, however, the ECDC Journal Eurosurveillance published a report on roughly 200 recruits in the Swiss Army - divided into 3 cohorts (symptomatically infected, asymptomatically infected, and not infected with SARS-CoV-2) - comparing their maximal aerobic capacity before and after a COVID-19 outbreak in their barracks.
First their brief description of the study:
In March 2020, we observed an outbreak of COVID-19 among a relatively homogenous group of 199 young (median age 21 years; 87% men) Swiss recruits. By comparing physical endurance before and in median 45 days after the outbreak, we found a significant decrease in predicted maximal aerobic capacity in COVID-19 convalescent but not in asymptomatically infected and SARS-CoV-2 naive recruits. This finding might be indicative of lung injury after apparently mild COVID-19 in young adults.
While the reduction in aerobic capacity among convalescent recruits is described as `significant' (at least, compared to the other cohorts), it does not appear to be profound. This is, admittedly, a small study and longer term observations are needed to determine if improvements in lung capacity of affected individuals improves over time.
The full Eurosurveillance report is well worth reading. I've only posted the link, and some excerpts from the discussion below.
Rapid communication Open Access
Reduced maximal aerobic capacity after COVID-19 in young adult recruits, Switzerland, May 2020
Discussion and conclusions
To our knowledge, changes in endurance or strength following SARS-CoV-2 infection, symptomatic or not, have not been described until now. We showed reduced aerobic capacity in young adult recruits 1 to 2 months after symptomatic COVID-19 while physical strength was unaffected. Ca 19% of COVID-19 convalescent recruits showed a decrease of VO2 max of more than 10% as compared with baseline before infection. Although our data do not explain the pathophysiology behind these findings, reduced VO2 max is a hallmark of interstitial lung disease . SARS-CoV-2 infection has been described to induce lung damage, even in asymptomatic cases . This indicates the importance of further long-term follow-up studies to assess the extent and duration of the sequelae, as well as of infection prevention to avoid these long-term consequences.
Physical deconditioning or demotivation may explain impaired fitness or compliance, respectively. The COVID-19 outbreak had a mental and physical impact on military personnel: stringent physical distancing measures, quarantine and isolation restricted possibilities for physical activity, and lowered morale. However, we would expect deconditioning and lowered test adherence due to demotivation to affect the results for both aerobic capacity and physical strength similarly , which was not the case with our observations.
Other than the described endurance run, we could neither conduct more specific tests (such as spirometry) nor perform serial imaging to identify our results’ pathophysiology. The cohort has meanwhile been dissolved due to the end of military training, thus such studies are difficult to perform in our study group. Since we studied a relatively homogeneous cohort of young, otherwise healthy, and predominantly male adults, our findings might not be applicable to other population groups.
Our observations were made within 1 to 2 months after the diagnosis of COVID-19 and follow-up studies should be conducted to determine whether the reduction in VO2 max is reversible. With ca 44,900 confirmed COVID-19 cases in Switzerland  as well as over 2.4 million in the European Union and Economic Area and the United Kingdom, respectively  and still increasing case numbers, evaluating possible long-term consequences of COVID-19 is becoming more important by the day.
While COVID-19 has proven to be a relatively low-mortality (1% +-) pandemic, its long term impact on individual health, our healthcare system, and society as a whole remains unknown, and may not become fully apparent for years.