The overarching importance of sleep was further emphasized during the pandemic of COVID-19. The subjects infected by COVID-19 frequently experience sleep disturbances; some are long-lasting problems and decrease the quality of life. Insomnia is the most studied sleep disorder associated with COVID-19. Insomnia affects patients who have experienced an infection and the general population. Good sleep is important in maintaining mental and physical health, including immune system functions. The interconnections between insomnia, the immune system, and COVID-19 are complex. Insomnia triggers numerous immune system dysregulations and makes individuals more vulnerable to respiratory infections. This narrative review overviews the influence of the COVID-19 pandemic on the immune system through sleep disorders.

Objective The study worked with depressive symptoms, anxiety score and cognitive functions in obstructive sleep apnea (OSA) patients treated with CPAP. Methods Eighty-one subjects with OSA and without psychiatric comorbidity were treated with CPAP for one year and completed the following scales and cognitive tests: Trail Making Test, Verbal Fluency Test, d2 Test, Beck Depression Inventory-II and Beck Anxiety Inventory. MINI ruled out psychiatric disorder. At the two months check-up, subjects were re-evaluated for depressive and anxiety symptoms, and after one year of CPAP treatment, subjects repeated cognitive tests and scales. Data about therapy adherence and effectiveness were obtained from the patient’s CPAP machines. Results The study was completed by 59 CPAP adherent patients and eight non-adherent patients. CPAP therapy effectiveness was verified in all patients by decreasing the apnea-hypopnoea index below 5 and/or 10% of baseline values. The adherent patients significantly improved depressive and anxiety symptoms. There was also an improvement in overall performance in the attention test; however, performance in many individual items did not change. The adherent patients also improved verbal fluency and in the Part B of the Trail making test. The non-adherent group significantly increased the number of mistakes made in the d2 test; other results were non-significant. Conclusion According to our results, OSA patients’ mood, anxiety and certain cognitive domains improved during the one-year therapy with CPAP. Trial Registration Number NCT03866161.