IntroductionThis study aimed to explore the impact of COVID-19 on the United Nations peacekeeping field hospitals where medical supply and manpower are extremely insufficient.MethodsA level II hospital was deployed in Wau, South Sudan, as the regional referral centre of the United Nations Mission in South Sudan (UNMISS). It had a total strength of 63 personnel with 47 medical staff (average age 38.3±8.0 years, 33 men). A new ‘appointment–triage–disinfection’ work pattern was adopted to cope with the COVID-19 outbreak in the mission. Data on medical service statistics and workload before/after the outbreak were collected and compared. The mental health of staff was analysed from the quarterly psychological survey, including Perceived Stress Scale (PSS)-10, Generalised Anxiety Disorder (GAD)-7 and Patient Health Questionnaire (PHQ)-9.ResultsThe number of outpatients decreased slightly after the COVID-19 outbreak (41.9±11.9 to 37.6±11.8 per week, p=0.49), whereas the weekly hospital length of stay of inpatients increased significantly (0.4±1.0 to 3.1±3.9 days, p=0.02). Total weekly working hours increased from 1884.9±34.1 to 2023.5±67.3 hours (p<0.001). Elevated mental stress (PSS-10: 4.3±2.4 in February to 7.5±3.9 in May, p<0.001; GAD-7: 4.0±2.3 to 9.4±4.0, p<0.001; PHQ-9: 2.1±1.2 to 3.2±2.4, p<0.001) was documented among healthcare providers after the outbreak. The threat of COVID-19 infection, delay in rotation and family-related concerns constituted the main stressors.ConclusionCOVID-19 imposes a huge pressure on peacekeeping field hospitals. Increased workload and mental stress among frontline healthcare providers deserve the attention of UNMISS officials. Facilitating the rotation of the medical staff might potentially improve the operational readiness of the hospital by bringing in well-trained personnel and sufficient medical supplies.