The ongoing COVID-19 pandemic, which was officially declared by the World Health Organization on March 11, 2020, has caused significant changes in multiple aspects of everyday life (1, 2). Government agencies around the world have responded to this unprecedented situation by implementing measures like mandatory mask use, social distancing, travel ban and curfew, retail stores closure, contact tracing, virus detection tests and quarantine (3–5). Since the first months of the implementation of those measures, a significant impact has been described on the mental health and sleep quality of the general population (6, 7).

It was previously reported that the prolonged confinement, in combination with the growing health concerns, have resulted in a reduction in the duration and the quality of sleep of the general population. These findings were, also, positively associated with depressive symptoms (8). Similar findings were reported in Greece, with symptoms of depression and being at higher levels in certain groups, such as the younger in age (9).

A special sub-group of the population, which has been greatly affected by the above-mentioned measures, are university students. One of the first measures applied was the suspension of the operation in all educational institutions, followed by the implementation of e-learning. Also, for medical students, the clinical practice and laboratory exercise of their curriculum were paused, leading to great changes in the educational process and consequently, in their daily life (10, 11).

The new major health risk, the strict preventive measures, and the radical changes in the lifestyle of medical students are reflected on the quality of their sleep and on their mental state, as described previously (12–15). Specifically, medical students, who were concerned about the effects of COVID-19 on education and work, reported higher rates of poor sleep quality (12). Additionally, according to studies conducted during the first months of the pandemic, they presented increased rates of depression and severe anxiety, fear of stigmatization due to association with the hospital environment and anxiety of meeting the demands of the new educational reality. These findings were more likely to be more common among the female population (13–15).

However, studies conducted during the second pandemic wave, when an outburst of COVID-19 cases was reported worldwide are scarce. During that time, even stricter preventive measures were enforced, since vaccinations had not been authorized. Simultaneously, on-line education was applied for the Autumn-Winter semester of the Academic Year 2020–2021, and only medical students of the final year were allowed to resume their clinical practice. The above-mentioned developments in the course of the pandemic have caused alterations in everyday life and probably could be associated with different findings in sleep and mental health of students.

The aim of the present study was to evaluate the impact of the situation that arose during the second year of COVID-19 pandemic, on the quality of sleep and mental health i.e., anxiety and depression, of medical students in Greece.

Our study captures the alterations in sleep quality and mental health of medical students in Greece during the second year of the COVID-19 pandemic. Overall, regarding sleep parameters, the respondents reported impaired sleep quality due to multiple sleep disturbances and decreased sleep duration; this was more obvious among 6th year medical students. Higher levels of insomnia, especially in females and increased fatigue in daily life were also reported. These alterations in sleep parameters were correlated with moderate to severe deterioration of mental health. Respondents presented also moderate to severe symptoms of anxiety and depression, to the point that a significant proportion admitted recurrent suicidal thoughts.

So far, contradictory findings are available in the literature regarding alterations in students' sleep schedule and sleep quality and the majority refers to the first year of the COVID-19 pandemic until the end of December 2020. A recent study conducted in 7 countries showed a prevalence of poor sleep among students worldwide and deficient sleep duration in more than one out of four students (23). These findings are in accordance with other studies that describe reduced night sleep duration and sleep efficiency due to sleep disturbances (24–26). Analogous conclusions have been drawn specifically for medical students and have been linked to disturbed daytime function (27). Notably, the senior medical students experienced significantly more intensely these alterations (12). However, in other studies insignificant changes in sleep quality (28) and an overall improvement in daily performance have been reported (29). Increased daytime napping though seems to offset sleep latency, thus total sleep duration remained unaffected (24). Increased total sleep time has also been mentioned, compared to the pre-pandemic period, especially among 6th year medical students (29). In our study, however, this specific population group reported the lowest sleep duration compared to students from other academic years. This can be possibly attributed to the resumption of their clinical practice and the clinical responsibilities during the pandemic, which may be linked with fear and anxiety, as previously shown (30).

Besides sleep schedule, during the COVID-19 health crisis, the mental health of students has been significantly affected. In our study 67.6 and 43.7% of the sample reported moderate to severe symptoms of anxiety and depression respectively. According to a recent systematic review by Batra et al. (31) performed in 15 countries, anxiety and depression levels reached 39.4 and 31.2% among university students, respectively. This study was conducted almost 1 year before our study, and thus during this period the psychological distress and depression have accumulated, possibly explaining the difference in our results (31). Interestingly, in two of the studies included in this systematic review almost one out of three and two out of three students, respectively, had suicidal ideation, which is surprisingly high compared to our results (32, 33). In our study, 16.7% of the respondents suffered from recurrent suicidal thoughts, which is in accordance with previous findings (34, 35). Furthermore, during the pandemic period, a rise in depression has been noted, with its severity and prevalence varying between different studies (12, 36–38). Additionally, the prevalence of PTSD symptoms, in those studies, was similarly elevated (31), with a higher degree of anxiety being attributed to increased concern about the impact of the COVID-19 pandemic (39) and the presence of a confirmed COVID-19 case in the proximal familial and friendly environment (40). This is also the case among medical students (36, 41), who experienced analogous levels of stress and anxiety symptoms (36, 37). According to our findings, infection in the immediate environment is associated with depression in a more severe way and PTSD symptoms, mainly in females.

Published literature associating gender and mental health is inconclusive, for example in the study by Xie et al. (12), males reported depressive symptoms more frequently, whereas Liu et al. found no statistically significant difference between gender with regards to anxiety and depression (37). However, Batra et al. (31) in their systematic review found that female students experienced higher levels of anxiety and stress. These results are consistent with our study. An interesting finding was that females having experienced COVID-19 either personally or in their proximal environment were significantly more affected than their male counterparts. A possible explanation could be that women in general, are more likely to report experiencing higher levels of anxiety (42) and that they are more affected by traumatic events (31).

Another finding in our study was the positive and independent correlation between insomnia, fatigue, dysfunctional sleep, depressive and anxiety symptoms. Previous studies confirm the association between sleep abnormalities and deteriorated mental health in students during the COVID-19 health crisis (26, 36). This comes as no surprise, since similar correlations have already been established, even before the pandemic. In a cross-sectional study of 95 medical students in Saudi Arabia stress, anxiety and depression were strongly linked with poor sleep (43). It was also reported that inadequate sleep duration and consequently fatigue may affect mental health to such a degree, that recurrent suicidal thoughts and even suicidal attempts may occur more frequently (44). Additionally, it has been demonstrated, both in the general population and specifically in medical students, that insomnia can be predictive of depression and anxiety (45, 46).

In a large study of the general population in Greece, Switzerland, Austria, Germany, France and Brazil, conducted during the first wave of the pandemic, total sleep time decreased and sleep quality in general improved in participants from Greece, compared to other countries (47). At the same time, insomnia affected 37.6% in a sample of the Greek population, which was significantly increased compared to the pre-pandemic period (48). As far as mental health is concerned, levels of anxiety and depression were notably elevated during the first COVID-19 wave. Fountoulakis et al. reported a significant increase in anxiety symptoms in over 45% and depressive symptoms in almost 40% of the participating Greek citizens (49). According to Patsali et al. major depression in the general population reached 12.43% (50). Focusing on Greek students, during the first pandemic wave, they experienced overall lower sleep quality despite an increase in their sleep duration (33). Our findings suggest an even higher prevalence of insomnia in our selected population (medical students) compared to the general population, affecting 65.9% of the participants. Kaparounaki et al. noted anxiety in 73%, depression in 60.9% and suicidal ideation in 20.2% in a Greek university sample (33). Meanwhile in a study conducted in the University of Patras by Sazakli et al., anxiety symptoms during COVID-19 pandemic decreased to 35.8% and depressive symptoms increased to 51.2% (51). Interestingly, in our study, anxiety levels were significantly higher and reached 67.6%. This also the case with our reported levels of depression, where overall 74.3% of the participants experienced it to some degree and 43.7% admitted having moderate to severe symptoms.

Our study certainly has limitations. Firstly, participation rate was relatively low; however, it is representative of the experiences of medical students since respondents came from all Greek Medical Schools. Additionally, examined parameters were assessed with the use of self-administered questionnaires in an on-line survey. On the other hand, we have used a large number of diagnostic tools, validated for the Greek population, and already used in several studies and thus are ensuring standardized results. In addition, this is, to the best of our knowledge, the first study to assess the impact of COVID-19 pandemic on sleep parameters of medical students in Greece, in association with a large series of sleep and mental health parameters.

In the aftermath of the COVID-19 pandemic, Greek medical students experienced, in a greater degree, sleep and mental health disorders such as insomnia, fatigue, poor sleep quality, anxiety, post-traumatic stress and depression. Thus, the need for better surveillance of students' wellbeing and subsequent counseling is even more evident now. A special focus must be given to the most affected groups such as female students.

The raw data supporting the conclusions of this article will be made available by the authors, upon request.

The study protocol, which involved human participants, was reviewed and approved by University General Hospital of Alexadroupolis Scientific Board. The patients/participants provided their informed consent to participate in this study.

AE, AR, and PS designed the study and wrote the manuscript. AA and EN contributed to the interpretation of the results and provided critical feedback. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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