Introduction

COVID-19 was an international health problem (Meller et al., 2022) that not only negatively affected physical health but also significantly impaired mental health (Holmes et al., 2020). According to Holmes et al. (2020), the COVID-19 pandemic might lead to an increase in the proportion of persons who experience anxiety, depression, and participate in risky behaviors (including self-harm and suicide). Yao, Chen, and Xu (2020) emphasized that the feelings of anxiety and depression of individuals could increase when they faced an outbreak of disease. In society, a sense of loss could result from losing direct social connections, loved ones, jobs, possibilities for education, leisure, freedoms, and supports (Holmes et al., 2020). Moreover, the death rate from COVID-19 is very high.

CV-19 F was defined as feeling worried about being infected with the coronavirus (Ahorsu et al., 2020; Quadros et al., 2021). It was a strong, natural feeling that led to a cascade of physiological changes in individuals when they perceived an impending threat. People might have a high level of fear of infection and death because COVID-19 cannot be controlled due to the lack of vaccines and possible treatments (Khan et al., 2022). In the general population, the prevalence of CV-19 F ranges from 18.1 to 45.2% (Quadros et al., 2021). Although people affected by this crisis have experienced significant mental health effects as a result of CV-19 F (Belen, 2022; Fitzpatrick et al., 2020), their demands for mental health care have largely gone unmet (Xiang et al., 2020). In Vietnam, the fourth wave of the COVID-19 epidemic began on April 27, 2021. During this outbreak, the disease spread widely and resulted in many deaths. In the fourth wave, 1,675,321 Vietnamese people were infected, and 31,632 died from COVID-19 (Toan, 2021). Vietnam was ranked 117th out of 230 countries and territories in terms of the number of infections per million people (Vietnam Ministry of Health, 2022), which may cause Vietnamese people to fear COVID-19.

Adolescence is a developmental transitional period between childhood and adulthood. During this period, adolescents undergo major biological, social, and psychological changes that increase their vulnerability to mental health problems (such as poor sleep quality, depression, and anxiety) (Wang et al., 2022). Due to the epidemic, the proportion of adolescents suffering from anxiety, depression, stress, poor sleep quality, and substance use has increased (Jones et al., 2021; Silva et al., 2022). Furthermore, social distancing could increase loneliness, social isolation, and dependence on social media among adolescents (Zhen et al., 2021), which in turn would take a toll on their mental health (Lee et al., 2022; Loades et al., 2020). The impact of CV-19 F on adolescents’ mental and physical health has been profound (Neiman et al., 2022; Wright et al., 2021). CV-19 F exacerbated stress, anxiety, fatigue, and depression and reduced vitality and general well-being among adolescents (Neiman et al., 2022; Wright et al., 2021).

Anxiety as a Mediator in the Association Between CV-19 F and Depression

Recently, the link between CV-19 F, anxiety, and depression has been reported in the literature. First, anxiety and depressive symptoms were observed to be exacerbated by CV-19 F (Erbiçer et al., 2021; Meller et al., 2022; Neiman et al., 2022; Rodríguez-Hidalgo et al., 2020). In a meta-analysis of 33 separate investigations, Erbiçer et al. (2021) revealed that CV-19 F was strongly associated with anxiety and depression levels in the general population. Similar results were found in samples of adolescents, young adults with inflammatory bowel disease (Neiman et al., 2022), and college students (Rodríguez-Hidalgo et al., 2020). People who feared COVID-19 amplified negative thoughts that impaired their mental health (Arora et al., 2020; Ahorsu et al., 2020). In addition, CV-19 F was related to excessive social media use; meanwhile, excessive social media use has been linked to anxiety and depression (Gao et al., 2020). Second, anxiety was found to be associated with depression in the context of COVID-19 (Havnen et al., 2020; Kausar et al., 2021). Individuals with high anxiety reported poor sleep quality, low perceived social support, and difficulty finding meaning in life, which in turn increased the risk of depression (Jacobson et al., 2017; Li et al., 2018; Shek et al., 2022). Finally, it was found that anxiety mediated the association between CV-19 F and depression among college students (Kausar et al., 2021; Rodríguez-Hidalgo et al., 2020). As a result, increased anxiety from CV-19 F could contribute to an increase in depressive symptoms among college students.

Sleep Quality as a Moderator in the Association Between CV-19 F and Anxiety

Sleep was essential for mental health. Worse sleep quality (insomnia and short sleep duration) was found to be associated with higher levels of anxiety and depression (Ben Simon et al., 2020; Sun et al., 2018). Therefore, poor sleep quality can exacerbate anxiety symptoms. In another aspect, CV-19 F was discovered to be associated with a decrease in sleep quality. According to Siddique, Ahmed, and Hossain (2021), CV-19 F increased stress symptoms, which in turn led to impaired sleep quality. In the COVID-19 pandemic, sleep-related problems increased symptoms of psychological distress (anxiety and depression) (Alimoradi et al., 2021; Meller et al., 2022). According to Diaz et al. (2022), short sleep and insomnia were associated with higher rates of anxiety and depression. Thus, both CV-19 F and poor sleep quality can become risk factors for anxiety.

Purpose of this Study

For the first time, this study examines the association between CV-19 F and depression in a sample of Vietnamese adolescents and proposes a moderated mediation model. So far, there have been no studies on the link between CV-19 F and mental health among Vietnamese adolescents. In the literature, a handful of studies explored the complex relationship between CV-19 F, anxiety, sleep quality, and depression (Kausar et al., 2021; Rodríguez-Hidalgo et al., 2020; Siddique et al., 2021) among college students and adults. However, there is a scarce study on associations between CV-19 F, sleep quality, anxiety, and depressive symptoms among adolescents.

This study sought to examine the relationship between CV-19 F and depression symptoms in adolescents, the underlying mechanisms of explanation and buffering for this relationship during this developmental stage. We developed two hypotheses (see Fig. 1) based on previous findings: (1) Anxiety would mediate the link between CV-19 F and depression, and (2) the mediating effect of CV-19 F on depression through anxiety would be dependent on sleep quality and more powerful when sleep quality was low.

Fig. 1
figure 1

Hypothetical model

Full size image

Methods

Sample and Procedure

The proposed model was tested with a convenience sample of 685 high school students from high schools in a small province in Vietnam (M = 16.09; SD = 0.860; 67.4% female; 37.1% of 10th grades; 32.0% of 11th grades; and 30.9% of 12th grades). Participants were invited to complete an online survey through their homeroom teachers. Participation in the study is completely voluntary. Therefore, if students do not want to participate in the study, they can opt out without consequences. Students who volunteered to participate in the study were invited into an online meeting room. At the online meeting room, students received a link to the online survey. Students took approximately 15 min to complete the online survey. The online survey ended, and students received a small gift (a link to download books and stories). All participants’ responses were confidential. Informed consent was obtained from all parents and participants.

Materials

Fear of COVID-19: The Fear of COVID-19 Scale (FCV-19 S) is a 7-item measure of CV-19 F (Ahorsu et al., 2020). Sample items include: “My heart races or palpitates when I think about getting coronavirus-19”, “I cannot sleep because I’m worrying about getting coronavirus-19”, “When watching news and stories about coronavirus-19 on social media, I become nervous or anxious”, “I am afraid of losing my life because of coronavirus-19”, “My hands become clammy when I think about coronavirus-19”, “It makes me uncomfortable to think about coronavirus-19”, and “I am most afraid of coronavirus-19”. Items are evaluated on a 5-point Likert scale from 1 to 5 (from “strongly disagree” to “strongly agree”). The FCV-19 S ranges from 7 to 35, with 35 being the most fearful. The FCV-19 S has been adapted to suit Vietnamese culture. The results of the reliability and validity test are as follows: Reliability (α = 0.866, αretest (after 10 days) = 0.878) and validity (χ2/df = 1.128 (< 5), GFI = 0.958 (> 0.90), CFI = 0.994 (> 0.90), NFI = 0.953 (> 0.90), TLI = 0.991 (> 0.90), RMSEA = 0.037 (< 0.08). In this study, the FCV-19 S has good reliability (α = 0.883).

Sleep quality: The Pittsburgh Sleep Quality Index (PSQI) (Buysse et al., 1989) is an 18-question self-reported measure of sleep quality. These 18 questions are used to measure 7 components of sleep (e.g., sleep latency, sleep disturbances, etc.). Many questions were evaluated on a 4-point Likert scale from 0 (not during the past month) to 3 (three or more times a week). A sample question includes “Have to get up to use the bathroom.” The range of the overall sleep quality score for the seven factors is 0 to 21. The sleep quality was poor, with a score of 21 being the worst. PSQI has been widely used in Vietnam. The internal consistency of the PSQI in this study was 0.751.

Anxiety and depression: The short version of the Depression Anxiety Stress Scales (DASS-21) is a 21-item measure of stress, anxiety, and depression symptoms. Items are evaluated on a 4-point Likert scale from 0 (never) to 3 (almost always). The highest possible score for each subscale is 42, while the lowest possible score is 0, with 42 points signifying the most stress, anxiety, or depressive symptoms. DASS 21 has been widely used in Vietnam. In this study, the authors used only anxiety and depression subscales. In our study, the internal consistency of the anxiety and depression subscales was 0.767 and 0.888, respectively.

Data Analysis

In this study, we used statistical software such as SPSS V20, Amos V20, and Process Macro V3.5. We first analyzed the reliability and validity of the scales. Then, we conducted analyses of descriptive statistics and correlation. Finally, we utilized SPSS PROCESS macro version 3.5 (Model 4 and Model 7) to examine all the hypotheses. Mediation analysis (Model 4) detects whether there is an indirect effect of CV-19 F on depression through anxiety. Moderated mediation analysis (Model 7) detects whether this indirect effect is dependent on the moderation of sleep quality. In the models, age and gender were controlled for in all analyses because preliminary analysis indicated that gender and age may influence the findings of this study (see Table 1).

Table 1 Preliminary analysis
Full size table

Findings

Preliminary Analysis

Results from the correlation analysis indicated that CV-19 F was positively related to sleep quality (r = 0.087, p < 0.05), anxiety (r = 0.156, p < 0.01), and depression (r = 0.075, p < 0.05). Sleep quality was positively related to anxiety (r = 0.441, p < 0.01) and depression (r = 0.423, p < 0.01). Anxiety was positively related to depression (r = 0.625, p < 0.01). Age and gender are related to CV-19 F and sleep quality (see Table 1).

Mediation Role of Anxiety in the Relation Between CV-19 F and Depression

Table 2 presents the results of the mediation analysis. Mediation analysis indicated that CV-19 F positively predicted anxiety (β = 0.158, p < 0.001) and anxiety positively predicted depression (β = 0.627, p < 0.001); however, CV-19 F did not predict depression (β= -0.023, p > 0.05). CV-19 F had a significant indirect effect on depression through anxiety (β = 0.099, SE = 0.027, 95% CI = [0.049, 0.154]).

Table 2 Mediation analysis (N = 685)
Full size table

Moderation Role of Sleep Quality

Table 3; Fig. 2 present the results of the moderated mediation analyses. Table 3 indicated that the CV-19 F did not predict depression (B = -0.035, p > 0.05) and anxiety (B= -0.059, p > 0.05), but anxiety positively predicted depression (B = 0.758, p < 0.001).

Table 3 Moderated mediation analysis (N = 685)
Full size table
Fig. 2
figure 2

Interaction effect of COVID-19 fear and sleep quality on anxiety

Full size image

The interaction between CV-19 F * sleep quality was significant (B = 0.033, p < 0.01, SE = 0.012, 95% CI = [0.009, 0.057]). Therefore, sleep quality moderated the association between CV-19 F and anxiety. The results indicated that the predictive effect of CV-19 F on anxiety was more powerful when sleep quality was low (B = 0.249, p < 0.001, SE = 0.056, 95% CI = [0.138, 0.359] rather than when sleep quality was high (B = 0.058, p > 0.05, SE = 0.054, 95% CI = [-0.047, 0.163] (see Fig. 2).

The results of the conditional indirect effects exploration indicated that the mediating effect of CV-19 F on depression through anxiety was more powerful when sleep quality was low (B = 0.188, SE = 0.051, 95% CI = [0.084, 0.286]) rather than when sleep quality was high (B = 0.044, SE = 0.036, 95% CI = [-0.027, 0.113]). The index of moderated mediation was significant (B = 0.025, SE = 0.010, 95% CI = [0.005, 0.044]). The above results showed that sleep quality moderated the indirect effect of CV-19 F on depression through anxiety.

Discussion

In recent years, the link between CV-19 F and anxiety and depression has attracted the attention of a number of researchers (Erbiçer et al., 2021; Meller et al., 2022). However, much less is known about the moderating role of sleep quality and the mediating effect of anxiety in the association between CV-19 F and depressive symptoms among adolescents. This study looked into the role of anxiety as a mediator and the role of sleep quality as a moderator in the relationship between CV-19 F and depressive symptoms among adolescents. Our findings showed that anxiety fully mediated the association between CV-19 F and depression symptoms, and sleep quality moderated this association.

Consistent with previous findings on samples of college students (Kausar et al., 2021; Rodríguez-Hidalgo et al., 2020), we found that anxiety mediated the link between CV-19 F and depression among Vietnamese adolescents. This finding demonstrated the validity of Hypothesis 1. Previous studies found that anxiety partially mediated this association between CV-19 F and depression (Kausar et al., 2021; Rodríguez-Hidalgo et al., 2020), while our study indicated that anxiety fully mediated this association. It may be a new finding of this study that has not been found in the literature before. According to our results, not all adolescents with CV-19 F are at risk for depression; only those with CV-19 F who have anxiety symptoms are at risk for depression. Therefore, intervention programs should only focus on at-risk adolescent groups. Based on previous studies, we explain that adolescents who fear COVID-19 may have negative thoughts and overuse social media, thereby developing anxiety symptoms (Ahorsu et al., 2020; Arora et al., 2020; Gao et al., 2020). Individuals who developed anxiety as a result of their fear of COVID-19 may later experience sleep problems and difficulty finding meaning in their lives, which may lead to depression (Li et al., 2018; Shek et al., 2022). Therefore, anxiety plays an important role in exacerbating depression in COVID-19-feared adolescents.

More importantly, the association between the CV-19 F and depression through anxiety was moderated by sleep quality. This finding demonstrated the validity of Hypothesis 2. When sleep quality was poor, the indirect predictive effect of CV-19 F on depression through anxiety was more pronounced. The link between CV-19 F and anxiety (Erbiçer et al., 2021; Gao et al., 2020; Meller et al., 2022) as well as between sleep quality and anxiety (Ben Simon et al., 2020; Diaz et al., 2022; Sun et al., 2018) were documented separately. The link between CV-19 F and depression mediated by anxiety was also demonstrated in the literature (Kausar et al., 2021; Rodríguez-Hidalgo et al., 2020). This is a novel addition since it is the first time that the indirect impact of CV-19 F on depression through anxiety that is tempered by sleep quality has been revealed. According to our results, not all adolescents with CV-19 F were at risk for depression; only those with both high anxiety levels and low sleep quality were at risk. Therefore, not only anxiety but also sleep quality is an important mechanism in the relationship between CV-19 F and depression in Vietnamese adolescents.

The fourth wave of the COVID-19 epidemic in Vietnam had a strong impact on adolescents. Firstly, while the disease spread so quickly, Vietnam lacked effective vaccines and treatments, which could increase the fear of getting infected and thereby developing mental disorders in adolescents. Second, social distancing reduced in-person physical contact while increasing online exposure and overuse of social media devices among adolescents, which may increase feelings of loneliness, social isolation, fear, and mental health problems. Finally, when it came to taking classes online, many adolescents had difficulty adjusting to online learning, which further contributed to their fear of COVID-19 and mental health issues. This fact highlights the necessity for further research into the mechanisms underlying the association between CV-19 F and mental health issues in Vietnamese adolescents. Previous studies found that anxiety mediated this association (Kausar et al., 2021; Rodríguez-Hidalgo et al., 2020). Therefore, we investigated whether anxiety mediates the association between CV-19 F and depression in Vietnamese adolescents.

Based on the findings of this study, we suggest measures to reduce CV-19 F and anxiety and improve the sleep quality of adolescents, which can prevent and alleviate their depression. Such measures can include strengthening communication to provide information about the COVID-19 epidemic; instructing and training adolescents on how to prevent and respond to epidemics; building a social support system, especially an online psychological counseling system for adolescents; strengthening instruction and support for adolescents in online learning; and improving anxiety-coping skills for adolescents. In addition, adolescents can benefit from yoga, mindfulness exercises, listening to classical music, and practicing yoga to get better sleep.

Previous research concentrated on the association between CV-19 F, anxiety, and depression in college students, whereas we offered new insights into this association in a sample of adolescents. The study also offered fresh perspectives on how sleep quality affects the indirect link between CV-19 F and anxiety-mediated depression that has never been reported in the previous literature. The findings of this study might help medical professionals or psychologists create depression prevention and alleviation plans for at-risk adolescents during COVID-19. Accordingly, depression prevention and alleviation plans for adolescents during the COVID-19 pandemic might focus on the complex relationship between CV-19 F, anxiety, sleep quality, and depression. The limitations of this study include that: (i) it did not clearly establish a causal link between CV-19 F, sleep quality, anxiety symptoms, and depression; (ii) the adolescents’ levels of CV-19 F, sleep quality, anxiety, and depression were assessed only with self-report scales. Therefore, these findings should be replicated in a longitudinally designed study with more objective data collection methods.