Indexed in MEDLINE, SCI & KoreaMed
pISSN 1011-8934   eISSN 1598-6357
Open Access, Peer-reviewed, Weekly
    J Korean Med Sci. 2023 Dec 18;38(49):e413. English.
    Published online Dec 05, 2023.
    https://doi.org/10.3346/jkms.2023.38.e413
    © 2023 The Korean Academy of Medical Sciences.
    Original Article

    Association Between Electronic Device Use at Bedtime and COVID-19 Vaccine-Related Adverse Events During the COVID-19 Pandemic in Korean Adults: A Nationwide Cross-Sectional Population-Based Study

    Kyung Wook Kang,1 Jiyoung Kim,2 Keun Tae Kim,3 Myeong-Kyu Kim,1 Yong Won Cho,3 and on behalf of the Sleep Epidemiology Committee of the Korean Sleep Research Society
      • 1Department of Neurology, Chonnam National University Hospital, Chonnam National University School of Medicine, Gwangju, Korea.
      • 2Department of Neurology, Pusan National University Hospital, Pusan National University School of Medicine, Busan, Korea.
      • 3Department of Neurology, Keimyung University School of Medicine, Daegu, Korea.
    • Address for Correspondence: Yong Won Cho, MD, PhD. Department of Neurology, Keimyung University School of Medicine, 1095 Dalgubeoldae-ro, Dalseo-gu, Daegu 42601, Republic of Korea. Email: neurocho@gmail.com
    Received June 22, 2023; Accepted September 14, 2023.

    This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

    Abstract

    Background

    The coronavirus disease 2019 (COVID-19) pandemic has led to heightened mood disturbances linked to increased electronic device use at bedtime (EUB). General anxiety may contribute to an increased likelihood of experiencing nocebo responses, which have been reported to be associated with COVID-19 vaccine-related adverse events (CAEs). However, no related studies have been conducted to examine this association to date.

    Methods

    We executed a nationwide cross-sectional study to explore these correlations during the pandemic. Using data from the 2022 National Sleep Survey of South Korea, we analyzed the sleep health of 4,000 adults aged 20–69 years between January and February 2022. Shift workers and those with severe sleep disorders were excluded. Participants with EUB more than four days a week were labeled as high frequency EUB, and those reporting CAEs after both vaccine doses were marked as having a presence of CAEs. The survey also included details about anthropometric data, socioeconomic status, and sleep status.

    Results

    Of the 3,702 participants, 92.6% had received two or more vaccine doses, with 41.2% experiencing CAEs. Furthermore, 73.7% had a high EUB frequency. Factors associated with CAE reporting included younger age, female sex, and high EUB frequency, while heavy alcohol use was found to be less likely to be associated with CAE reporting. Notably, a high EUB frequency was significantly associated with reported CAEs (odds ratio, 1.223; 95% confidence interval, 1.028–1.455; P = 0.023).

    Conclusion

    A nationwide online survey conducted in South Korea during the pandemic found that individuals who engaged in the relatively frequent use of electronic devices during bedtime had worse sleep quality and increased COVID-19-related adverse events compared with those using these devices less frequently. These findings have the potential to enhance our understanding of the impact of the use of electronic devices at bedtime on health.

    Graphical Abstract

    Keywords
    COVID-19 Vaccine; Nocebo Effect; Adverse Events; Smartphone; Epidemiological Study

    INTRODUCTION

    The number of smartphone users has increased dramatically over the past few decades, affecting approximately half the global population.1 Unsurprisingly, South Korea, which has a reputation for embracing new technologies and where most consumers adapt quickly to new trends, is no exception. The smartphone penetration rate among South Koreans is consistently increasing, reaching 92.7% according to a survey conducted in 2021.2

    Despite the many benefits of smartphones, excessively using them can negatively impact physical and psychological health.1, 3, 4, 5, 6, 7, 8, 9 In a cross-sectional study of Chinese junior middle school students, smartphone addiction, defined as using the Smartphone Addiction Scale-Short Version, was found to double the likelihood of developing hypertension.5 Furthermore, a South Korean survey revealed that university students who used their smartphones for over 4–5 hours daily were at an increased risk for developing depression.1 A comprehensive review also revealed a consistent relationship between excessive smartphone use and psychological health, including anxiety and depression.8

    Problematic smartphone use (PSU) refers to excessive mobile phone use that may be related to health issues.10 With PSU increasing worldwide over time,11 particularly during the COVID-19 pandemic,12, 13 researchers have focused on its negative health effects. Several studies have found significant links between PSU and psychological and sleep problems.3, 14, 15, 16 One mechanism contributing to sleep problems in individuals with PSU is their tendency to engage in electronic device use at bedtime (EUB), which shortens their sleep time.16, 17 Furthermore, sleep problems caused by EUB can affect daily life.15, 18, 19 According to a web-based study of Australian adults, engaging in EUB for at least two or three nights per week during the previous seven days was associated with daytime problems.19 As the COVID-19 pandemic may trigger or worsen PSU,13 health and sleep problems resulting from EUB could occur.20

    People may have resorted to PSU and EUB as coping mechanisms during the COVID-19 pandemic, which subsequently affects their sleep and causes emotional disturbances.1, 3, 4, 7, 21, 22, 23 Emotional disturbances can be linked to COVID-19 vaccine-related adverse events (CAEs) through the nocebo effect.24, 25 As with its placebo counterpart, the nocebo effect involves the experience of negative symptoms after exposure to an inert substance.26 Herein, the nocebo included common nonspecific symptoms, such as headache and fatigue after COVID-19 vaccination.24 A systematic review and meta-analysis of randomized clinical trials of experimental COVID-19 vaccines showed that adverse events were associated with the nocebo effect.24 Although nocebo-related adverse events were non-serious in this study, side effects can make the vaccination experience unpleasant. Concerns about such side effects are among the most common reasons for vaccine hesitancy.27 Given the importance of positive attitudes towards vaccines for achieving herd immunity, studies examining factors related to the nocebo effect are crucial in preparing for potential future viral outbreaks.

    In today’s increasingly digitized society, we cannot ignore the role of electronic devices, particularly smartphones, as lifestyle factors. Their usage, which notably increased during the COVID-19 pandemic, has been associated with mood disturbances.8, 12 Therefore, this may warrant significant consideration in public health strategies for vaccine campaigns. Previous studies have revealed links between mood disturbances and nocebo effects,28 as well as between mood disturbances and EUB.29, 30 As such, we speculate that there may be an association between EUB and CAEs. However, evidence supporting the influence of EUB on CAEs remains scarce. In this nationwide Korean study conducted during the COVID-19 pandemic, we aimed to evaluate the relationship between EUB and CAEs.

    METHODS

    Participants and procedures

    The data for this study were derived from the 2022 National Sleep Survey of South Korea. This survey, initiated by the Epidemiology Committee of the Korean Sleep Research Society, was a nationwide, cross-sectional online survey designed to investigate sleep health among South Koreans aged 20–69 years. It was conducted from January to February 2022 during the COVID-19 pandemic.31 The survey was carried out by Embrain public company, which maintains a panel of over 1.5 million individuals. Our study selectively included adults from these voluntary panels. With a ± 1.55-point sampling error at a 95% confidence interval, the minimum target population for this study was 3,998. This is because the number of individuals in our target age group in South Korea was 37,133,171 in 2021. We arrived at a final sample of 4,000 individuals, using proportional stratified sampling based on the 2021 Korean Census data for age, sex, occupation, and income.

    We excluded shift workers (n = 271) because our focus was to study individuals from the general population who failed to sleep well despite having no actual constraints regarding bedtime. We also excluded participants (n = 27) who reported very short (< 3 hours) or very long sleep durations (> 13 hours), as they were likely to have serious sleep disorders. This study was approved by the Institutional Review Board (IRB) of Keimyung University Hospital (IRB No. DSMC 2021-12-063). All the participants provided written informed consent. Additional details about the study methodology, in accordance with the Checklist for Reporting Results of Internet E-Surveys (CHERRIES), can be found in Supplementary Table 1.

    Measures

    Demographic information

    All participants (n = 3,702) provided basic demographic information through a well-established questionnaire. This included information regarding age, sex, presence of sleep partner, employment status, education level, monthly family income, and alcohol and smoking habits. Anthropometric data such as weight and height were also collected.

    We collected monthly family income data in units of 1 million won (approximately USD 833), ranging from less than 2 million won (approximately USD 1,666) to over 10 million won (approximately USD 8,330). Income was then categorized as being greater or less than 5 million won following findings of the Basic Living Review Committee of the Korean Ministry of Health and Welfare, whose 2021 determination was that the median income for a family of four was 4.87 million won.

    Alcohol consumption was examined in terms of drinking frequency, type of alcohol, and the average amount consumed. At-risk drinking for South Koreans was defined based on the modified guidelines of the National Institute on Alcohol Abuse and Alcoholism.32 Heavy alcohol consumption was defined as drinking more than eight drinks per week (1 drink = 14 g alcohol) for men under 65 years and more than four drinks per week for men aged 65 years and older. For women, the criteria were half of those for men. Binge drinking was defined as more than three drinks per day for men under 65 years of age and more than two drinks per day for men aged 65 years or older. For women, the criteria were more than two drinks per day for those under 65 years of age and more than one drink per day for those aged 65 years or older.

    Smoking status categories were nonsmokers or smokers. Participants who had never smoked were regarded as non-smokers, whereas those who had smoked at least once in their lives were classified as smokers. Body mass index (BMI) was calculated by dividing body weight by the square of height. Obesity was defined as BMI ≥ 25 kg/m2.

    Electronic device use during bedtime and sleep measures

    We asked participants about their use of smartphones and tablets during bedtime, as these devices are shown to be significant sources of EUB in a previous study.33 Participants were asked how many nights a week, on average, they had used their smartphone or tablet at bedtime in the past 7 days. Response options included “not at all,” “1–3 nights,” “4–6 nights,” and “all nights.” However, a previous Austrian study showed that technology use at least two or three nights per week was associated with daytime dysfunction and mental health issues.19 In order to clearly understand the detrimental effects of EUB on health, we decided to categorize the variables into two response options: “less than 4 days” and “more than 4 days” in the past week.

    We examined sleep-related variables such as sleep onset latency (SOL), sleep duration, and sleep satisfaction level. Participants rated their sleep satisfaction based on a 5-point Likert scale (1 = very satisfactory, 2 = satisfactory, 3 = moderate, 4 = unsatisfactory, 5 = very unsatisfactory) and their actual sleep time in the past four weeks rather than the time they spent lying in bed. The average sleep duration and latency were calculated using the following formula: [(weekday value × 5) + (weekend value × 2) /7], after asking about sleep duration and latency on weekdays and weekends. Our survey used the Epworth Sleepiness Scale (ESS) to assess daytime sleepiness.

    COVID-19 vaccine-related adverse events

    Our questionnaire included questions about COVID-19, such as whether the respondent had experienced any CAEs and their vaccination history related to COVID-19. The presence of CAEs was investigated only in participants who received at least two vaccine doses. Our study aimed to encompass various CAEs, regardless of the severity of adverse events following COVID-19 vaccination. Therefore, CAE was measured using the following single questions: “ Have you experienced any adverse events from the COVID-19 vaccination?” We only recorded the experience of CAEs and did not analyze their severity.

    Statistical analyses

    Statistical analyses were performed using SPSS version 22 (IBM Corp., Armonk, NY, USA). Continuous variables were compared using Student’s t-test, while categorical variables were compared using Pearson’s chi-square test. Multivariate logistic regression analysis was performed to evaluate the factors affecting a higher frequency of EUB and the presence of CAEs. These models were adjusted for covariates that showed P values < 0.1 in the univariate analyses. Results were expressed as odds ratios (OR) with 95% confidence intervals (CI), and statistical significance was defined as a two-tailed P value of < 0.05.

    Ethics statement

    This study was approved by the IRB of Keimyung University Hospital (IRB No. DSMC 2021-12-063). All participants provided written informed consent for this study.

    RESULTS

    The mean age of the 3,702 adults surveyed was 44.74 ± 13.36 years, with 1,873 (50.6%) being a woman. Regarding socioeconomic status, participants responded as follows: 2,001 (54.1%) reported sharing a bed with a person such as a partner, spouse, or children; 2,563 (69.2%) reported being currently employed; 2,832 (76.5%) reported having a level of education above university level; and 2,296 (62.0%) reported having a family income of less than 5 million won (Table 1). Nearly three-quarters (2,729; 73.7%) were engaged in four or more days of EUB in the past week (Table 1).

    Table 1
    Clinical information according to the frequency of electronic device usage at bedtime

    These individuals were significantly more likely to be younger, female, smokers, and did not share a bed with someone else. These associations remained significant even after adjusting for covariates (Table 2).

    Table 2
    Predictors of the high-frequency electronic device use at bedtime

    Association between sleep and electronic device use at bedtime

    Table 3 shows that participants with more than four days of EUB per week had shorter mean sleep duration, longer SOL, higher ESS scores, and unsatisfactory self-reported sleep. Despite no significant difference in weekday sleep duration between the groups, those with frequent episodes of EUB per week had a longer mean and weekend sleep duration than those with fewer than four days of EUB per week. After adjusting for covariates, high EUB frequency was significantly associated with longer SOL, unsatisfactory sleep, and higher ESS scores.

    Table 3
    Association between sleep parameters and the frequency of electronic device use at bedtime

    Participants with a high EUB frequency were less satisfied with their sleep quality. We calculated the ratio of the percentage of participants in each group who reported each level of sleep satisfaction on the Likert scale. For each satisfaction level, the denominator represented the percentage of participants who reported that level of satisfaction among those who reported fewer than four days per week of EUB, whereas the numerator represented the percentage with more than four days per week of EUB among that level. The ratio increased with higher levels of unsatisfactory self-reported sleep reported on the Likert scale (Fig. 1). Even after adjusting for covariates, the association between a high EUB frequency and unsatisfactory self-reported sleep persisted (Table 3).

    Fig. 1
    Differences in self-reported sleep satisfaction according to the frequency of electronic device use at bedtime. The percentage ratio (B/A) of self-reported sleep satisfaction was compared between participants (A) who reported using electronic devices at bedtime less frequently (< 4 days/week) and those (B) who reported using electronic devices at bedtime more frequently (≥ 4 days/week).
    EUB = electronic device use at bedtime.

    Association between COVID-19 vaccine-related adverse events and electronic device use at bedtime

    Of the total participants, 3,427 (92.6%) received two or more vaccine doses, and 1,411 (41.2%) of those individuals experienced CAEs. Among those with CAEs, there was a higher percentage of women (59.1% vs. 43.7%, P < 0.001) and younger individuals (42.63 ± 13.08 vs. 46.60 ± 13.35, P < 0.001). Moreover, individuals with higher alcohol consumption and binge drinking were less likely to report CAEs (Table 4). After adjusting for covariates, the protective effect against CAEs remained significant for higher alcohol consumption, but not for binge drinking (Table 5). CAEs were more likely to occur in the group with a high frequency of EUB (Table 4).

    Table 4
    Association between the presence of adverse events from the COVID-19 vaccines and other variables

    Table 5
    Multivariate logistic regression analysis for the presence of adverse events from coronavirus disease 2019 vaccines

    In multivariate logistic regression analyses, participants with CAEs were more likely to be women and younger, have shorter mean sleep durations, longer mean SOL, and report more unsatisfactory sleep. An EUB frequency exceeding four days per week was significantly associated with CAEs (Table 5; OR, 1.223; 95% CI, 1.028–1.455; P = 0.023).

    DISCUSSION

    We investigated the frequency of EUB per week and its association with sleep quality and CAEs. Our findings revealed that frequent EUB (more than four days per week) was associated with self-reported sleep dissatisfaction, longer SOL, and higher ESS scores, consistent with previous studies.18, 19, 29, 34, 35 A systematic review found that bedtime mobile phone use was associated with shorter sleep duration and lower sleep quality, although most studies used self-reported sleep outcomes.35 However, previous research has mainly focused on adolescents,15 with a few studies examining the relationship between EUB and sleep in adult populations.19, 29, 30, 34, 35 Most of these adult studies involved young adults in their 20s.30, 35 In adults, the effect of EUB on sleep differs from that in adolescents and young adults. A cross-sectional study that included 844 Belgian adults (aged 18–94 years) found that bedtime mobile phone use was significantly associated with poor self-reported sleep quality and longer SOL, but not with sleep duration.34 Our results support this finding, confirming the relationship between EUB frequency and self-reported sleep quality.

    Bedtime procrastination (BP), which has been extensively studied in relation to evening technology use, is defined as the act of going to bed later than intended, despite there being no external circumstances that prevent an individual from doing so.36 The concept of BP is not exactly the same as that of EUB; however, they have similarities. Similar to EUB,17 BP tied to PSU is significantly associated with anxiety and depression.9 Interestingly, several studies have found an increase in PSU and BP during the COVID-19 pandemic compared with the pre-pandemic period,12, 13, 22, 37 such as a Chinese study that showed higher BP scale scores in the post-compared with the pre-COVID-19 outbreak group.37 Increased anxiety and depression during the COVID-19 pandemic23, 38, 39 could have contributed to the rising prevalence of PSU and BP.9, 22, 37

    However, as internet-connected devices become smaller, the EUB, another problematic behavior, is also known to be correlated with PSU.17 It relates to delays in going to sleep due to using electronic devices while already in bed, unlike BP, which focuses on behaviors preceding bedtime.40 Although a considerable amount of evidence links EUB to physical and mental health symptoms,18, 29, 30, 34 less research has focused on exploring the effect of EUB on mental health compared to BP. This is primarily because the bedtime procrastination scale used to evaluate BP, which is widely used in related studies so far, does not include the item that can evaluate EUB.36 However, considering the detrimental effects of mobile phone use in bed after light out on sleep outcome,34 EUB may be more significant for our health than BP itself.

    In our study, we observed a correlation between an increased frequency of EUB and CAEs. This correlation may arise from evidence suggesting that EUB is not only linked with sleep disturbances but also with emotional disturbances.29, 30 Given the documented rise in mood disturbances during the COVID-19 pandemic,12, 13 we theorize that more people might resort to PSU as a maladaptive coping strategy in the face of heightened stress. Consequently, those who frequently experience EUB due to PSU might be more prone to poor sleep quality. Considering the established bidirectional relationship between sleep and mood disturbances,41, 42 emotional disturbances, which might be worsened by poor sleep quality (resulting in turn from frequent EUB), could contribute to the nocebo effect. This effect has been noted as a factor in non-specific CAEs in prior COVID-19 vaccine randomized controlled trials (RCTs) and has tied to emotional disturbances.24, 25 Therefore, we believe that EUB could contribute to an increase in CAEs during the COVID-19 pandemic.

    While we do not yet understand the causal relationship between the EUB and emotional disturbances due to the limited number of longitudinal studies, one such study has shown results that contradict our hypothesis. This longitudinal study of 815 young adults found that nighttime smartphone use was associated with higher levels of perceived stress and depressive symptoms at baseline. However, these differences were minor after an average four-month follow-up period.30 The results should be interpreted with caution, however, because the variables related to nighttime smartphone use were classified into 3 groups (0 Night, 1-3 Nights, > 3 Nights), based on the number of nights with less than six consecutive hours of sleep due to smartphone activities over a 16-week period. Notably, the most frequent disruptions (> 3 Nights) only consisted of 45 participants. Furthermore, the recorded nightly smartphone activity could potentially be underestimated, as it did not consider all relevant activities carried out using the smartphone.30 Contrarily, previous cross-sectional studies have almost always shown significant associations between EUB and emotional disturbances such as anxiety and depression.19, 29

    The inconsistency in results is likely because the detrimental effect of nighttime smartphone use on mental health is not based on a dose-response relationship, but rather depends on the frequency of smartphone use, which is not yet well-defined. In fact, an Australian study involving a sample of adult participants reported that those who experienced EUB for at least two nights in the past week were significantly more likely to report mood disturbances.19 Similarly, in our study, EUB for more than four days per week showed a noticeable correlation with CAEs compared to use for fewer than four days (Supplementary Fig. 1).

    Considering a significant relationship between sleep and mood disturbances,41, 42 it is unsurprising in our study that participants with a higher frequency of EUB were more likely to report unsatisfactory sleep. A study from South Korea echoed our results, revealing that smartphone overuse is tied to depression and delayed bedtimes among university students.1 Another study further confirmed that, during the COVID-19 pandemic, smartphone overuse correlated with lower sleep quality and delayed sleep phases among Korean middle school students.43 One potential intervention could be to curtail mobile phone use at bedtime. Supporting this idea, a small-sized RCT found that restricting mobile phone use before bedtime for a period of four weeks enhanced participants’ sleep profiles and positive affect.44 A meta-analysis of 65 RCTs, encompassing 72 interventions targeting sleep quality improvement, indicated that enhanced sleep mitigated symptoms of depression, anxiety, and stress.41 Furthermore, our study showed that having a sleep partner decreased the weekly frequency of EUB. This reduction could be associated with the positive mental health effects of bed-sharing,45 which underscores the connection between anxiety and EUB. Therefore, we further speculate that participants with a high frequency of EUB may have experienced elevated anxiety during the COVID-19 pandemic.6, 8, 9, 19, 22, 37 Although our study did not use anxiety or depression scales, preventing a direct causal inference between EUB and mood disturbance, there’s evident interaction between these factors. Further research is needed to elucidate this relationship.

    Psychological factors are known to be linked to the nocebo effect,25, 46 the frequency of EUB, and sleep quality.19 Consistent with this, our study found that participants who frequently experienced EUB or had unsatisfactory sleep were at a greater risk of reporting CAEs after receiving COVID-19 vaccine. These associations remained significant even after the adjustment of covariates, including various sleep parameters (Table 5). Furthermore, our research supports previous findings that CAEs are more common among women and younger individuals, highlighting the observed age and sex differences.47

    Our study revealed some noteworthy findings regarding alcohol consumption. Participants with higher alcohol consumption (measured in grams per week) and heavy drinking had a lower risk of CAEs. Two potential explanations are as follows: first, excessive alcohol intake may modulate immunity, potentially reducing COVID-19 vaccine effectiveness.48 Second, it could be a defense mechanism against increasing anxiety and stress from COVID-19 pandemic-related social circumstances, possibly decreasing it. Following the global lockdown, alcohol consumption significantly increased,48, 49 particularly in South Korea, where drinking is a popular leisure activity linked to peer pressure.32, 49 In a study of middle-aged Korean adults during the COVID-19 pandemic, higher friend support led to excessive alcohol consumption.49 Further, a Vietnamese study found that sharing emotions with friends reduced anxiety and stress during the COVID-19 pandemic.39 Therefore, owing to the friend support gained by alcohol consumption, stable mental health may have protected participants against CAEs in our study by reducing the frequency of the nocebo effect.

    This study had some limitations. First, since our study did not include mental health questionnaires, we assumed that excessive EUB is related to mood disturbances, such as depression or anxiety, to interpret our results. However, previous studies17 have confirmed that EUB is significantly associated with PSU, which has been linked to anxiety and depression.6, 8, 35 Additionally, an earlier study has reported a direct relationship between bedtime smartphone use and mood disturbances.30 Second, the causality among EUB frequency, mental health, sleep, and CAEs was difficult to infer from our cross-sectional study. However, an intervention that restricted mobile phone use before bedtime for four weeks showed improved sleep status, positive affect, and working memory in a previous study.44 Further research is needed to clarify the causality and develop treatments for patients with frequent EUB or sleep and mood disturbances. Third, it is difficult to generalize our results because our study included Korean adults during a specific period: the COVID-19 pandemic. Average smartphone use and the prevalence of PSU were found to be significantly higher in Korea than in other countries.1, 50 Additionally, the COVID-19 pandemic has been associated with high levels of mood disturbances worldwide, including stress, anxiety and depression.23, 37 Moreover, the survey time for the frequency of EUB and sleep profile does not precisely align with the time when CAEs occurred. As a result, the association between EUB, sleep, and CAEs may have been overestimated. Finally, our results were not adjusted for participants’ physical comorbidities, which could affect their sleep quality and mood disturbances, because our questionnaire focused solely on sleep status or sleep disorders.

    In conclusion, we found that participants with a higher frequency of EUB were more likely to report poorer sleep and CAEs after the COVID-19 vaccination during the pandemic compared with those with a lower frequency of EUB. We hypothesized that mood disturbances might act as intervening factors in these associations. However, to further support our suggestions, additional studies are required with improved research methods. These should include questionnaires to evaluate mental health of participants from diverse countries.

    SUPPLEMENTARY MATERIALS

    Supplementary Table 1

    CHERRIES checklist for web-based studies (adapted from Eysenbach 2004)

    Click here to view.(46K, doc)

    Supplementary Fig. 1

    The percentage of participants with COVID-19 vaccine-related adverse events according to the weekly frequency of electronic device use at bedtime. P value derived from linear by linear association.

    Click here to view.(55K, doc)

    Notes

    Funding:This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MIST) (2022R1F1A1064543).

    Disclosure:The authors have no potential conflicts of interest to disclose.

    Authors Contributions:

    • Conceptualization: Kang KW, Kim M, Kim J, Cho YW.

    • Data curation: Kang KW, Kim M, Kim J, Kim KT, Cho YW.

    • Formal analysis: Kang KW, Cho YW.

    • Investigation: Kang KW.

    • Methodology: Kang KW, Kim KT.

    • Writing - original draft: Kang KW.

    • Writing – review & editing: Cho YW.

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    MeSH Terms
    Adult*
    Anxiety
    COVID-19 Vaccines
    COVID-19*
    Cross-Sectional Studies
    Epidemiologic Studies
    Female
    Humans
    Korea
    Nocebo Effect
    Occupational Groups
    Pandemics
    Sleep Quality
    Sleep Wake Disorders
    Smartphone
    Social Class
    Vaccines
    Metrics
    Share
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