Background The medium-long impact of coronavirus disease 2019 (COVID-19) on active populations is yet to be fully understood, with potential individual and operational impact on military service personnel (SP). The M-COVID study was established to investigate cardiopulmonary, functional, cognitive, and mental health post-COVID-19 SP outcomes, across the spectrum of acute COVID-19 severity.

Method Observational four-cohort study; hospitalised, community-based illness with on-going symptoms (communitysymptomatic), community-based illness now recovered (community-recovered) and age, sex, job-role matched control. Participants underwent extensive clinical assessment involving cardiopulmonary imaging, submaximal and maximal exercise testing, pulmonary function, cognitive assessment, blood tests, electrocardiogram and questionnaires on mental health and physical function.

Results 113 participants (aged 39±9, 86% male) were recruited; Hospitalised (n=35), community-symptomatic (n=34), community-recovered (n=18) and control (n=26), 159±72 days following acute illness. Hospitalised and community-symptomatic groups were older (p=0.003), with a higher body mass index (p<0.001), and worse mental health (anxiety,p=0.011;depression,p<0.001;post-traumatic stress, p<0.001), fatigue (p<0.001), and quality of life scores (p=0.001), with a mean of 2±2 and 2±1 symptoms, respectively. Hospitalised and community-symptomatic participants also performed less well on sub-maximal (p<0.001) and maximal exercise testing, with hospitalised individuals displaying impaired ventilatory efficiency (p<0.001), less work at the anaerobic threshold and at peak (both p<0.001), and significantly reduced forced vital capacity (p=0.004). Clinically significant abnormal cardiopulmonary imaging findings were present in 6% of hospitalised participants, lower than those seen in other studies. Those who recovered from communitybased, mild-moderate COVID-19 had no significant differences from controls on any parameter.

Conclusions Recovered SP who suffered mild-moderate COVID-19 do not differ from an age, sex and job-role matched controls. This is reassuring for the vast majority of individuals who have had acute COVID-19 not requiring hospital management. Individuals who were hospitalised or continue to suffer symptoms may require a specific, comprehensive clinical and occupational assessment prior to a full return to duty.