A systematic review of the mental health changes of children and young people before and during the COVID-19 pandemic

There is increasing knowledge that the COVID-19 pandemic has had an impact on mental health of children and young people. However, the global evidence of mental health changes before compared to during the COVID-19 pandemic focusing on children and young people has not been systematically reviewed. This systematic review examined longitudinal and repeated cross-sectional studies comparing before and during COVID-19 pandemic data to determine whether the mental health of children and young people had changed before and during the COVID-19 pandemic. The Web of Science, PubMed, Embase and PsycINFO databases were searched to identify peer-reviewed studies that had been published in English and focused on children and young people between 0 and 24 years of age. This identified 21 studies from 11 countries, covering more than 96,000 subjects from 3 to 24 years of age. Pre-pandemic and pandemic data were compared. Most studies reported longitudinal deterioration in the mental health of adolescents and young people, with increased depression, anxiety and psychological distress after the pandemic started. Other findings included deteriorated negative affect, mental well-being and increased loneliness. Comparing data for pandemic and pre-pandemic periods showed that the COVID-19 pandemic may negatively impact the mental health of children and young people. There is an urgent need for high-quality research to address the impact, risks and protective factors of the pandemic on their mental health, as this will provide a good foundation for dealing with future health emergencies and other crises. Supplementary Information The online version contains supplementary material available at 10.1007/s00787-022-02060-0.


Introduction
There is growing concern about the negative effects that the COVID-19 pandemic is having on the mental health of children and young people, particularly those who are already vulnerable. A number of factors have contributed to mental health issues in these age groups, including emotional, physiological and behavioral stress. These have been due to factors such as social isolation, due to school closures, parental stress about the virus and employment, increases in undetected child abuse, increased cyber bullying, due to more online activities, and the trauma of losing family members [1,2]. In addition, the COVID-19 pandemic Laura Kauhanen and Wan Mohd Azam Wan Mohd Yunus contributed equally to this work and are joint first authors. 1 3 may have increased loneliness, depression and anxiety and decreased life satisfaction [3]. Increased suicidality and suicide attempts by adolescents during the pandemic has also been reported [4]. Lockdowns and physical distancing may have had a different impact on some children and young people, depending on their age, gender, ethnicity, family circumstances, socioeconomic situation and any pre-existing mental health problems [5][6][7][8].
To our knowledge, five systematic reviews have been published on the mental health of children and young people during the COVID-19 pandemic, four in 2021 and one in 2020. Meherali et al. and Nearchou et al. only included cross-sectional studies carried out at one time-point [9,10]. Racine et al. conducted a meta-analysis, which reported that the global prevalence of anxiety and depression among children and adolescent were 25.2% and 20.5% with 95% confidence intervals (CI) of 21.2-29.7 and 17.2-24.4, respectively, for the period from February to July 2020 [11]. Samji et al. attempted a broader systematic review, by examining 116 papers with any empirical study design [12], while Panchal et al. systematic review included 61 papers [13]. However, more than 70% included studies in both reviews were cross-sectional studies and they also included specific clinical subgroups. This makes it difficult to discern the mental health changes before and during the COVID-19 pandemic toward the general children and young people population samples. Samji et al. have stated that the priority for COVID-19 research should be representative samples and/or longitudinal follow-up studies that have the potential to demonstrate changes in mental health symptoms before and after the pandemic [12].
Different indicators for mental health problems should be measured repeatedly before and during the COVID-19 pandemic to assess changes in mental health trends during the pandemic. These should use directly comparable measures, sampling designs and convergent information from multiple sources, such as parents, teachers and children [14,15].
The aim of this study was to conduct a systematic review of the existing global literature, so that we could compare the mental health of children and young people aged 0-24, before and during the COVID-19 pandemic, and identify any changes.

Search strategy
The review study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [16]. The protocol of the review was prospectively registered with the International Prospective Register of Systematic Reviews (PROSPERO number: CRD42021238999).
The Web of Science, PubMed, Embase and PsycINFO electronic databases were used to identify peer-reviewed papers published in English from 1 January 2020 to 22 March 2021. The search syntax for each database is listed in Table S1 in the Supplementary Appendix. We also used the backward snowballing technique to search for other relevant papers [17], by looking at the reference lists of the selected papers.

Inclusion and exclusion criteria
Studies with children and young people aged 0-24 years were included. Children were defined as 0-9 years old and young people as 10-24 years of age. We refer to the definition of adolescents (10-19 years old) and young people (10-24 years old) by the World Health Organization [18,19] that include adolescents as defined by Sawyer et al. (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) years old) [20]. Population, community or schoolbased studies were included. We did not include studies that focused on individuals aged 25 or older or studies that did not report the specific age ranges of the subjects.
The review included any observational studies that used surveys or interviews to determine the mental health symptoms of subjects before and during the pandemic. These included longitudinal, repeated cross-sectional, cohort, panel, time series and time trend studies. We excluded single cross-sectional studies, studies that using modeling to predict the impact of the pandemic on mental health or studies that used different measures to compare outcomes before and during the pandemic. The periods before and during the pandemic were the pandemic periods defined by the authors of the included studies and at least one corresponding prepandemic period. It is worth noting that we have previously reported findings on the registered mental health service use, self-harm and suicides based on administrative data [21] so these types of studies were also excluded in this review.
The following mental health outcomes were included; externalizing and internalizing problems, attention-deficit/hyperactivity problems, negative and positive effects, depression, anxiety, psychological distress, health-related quality of life, peer problems and loneliness. Only studies that reported at least one validated measure of these mental health outcomes before and during the COVID-19 pandemic were included. The studies were only included if the same measures and/or methods were used for each outcome before and during the pandemic.

Study selection and retrieval process
The screening and study selection processes were independently conducted by two reviewers (LK and WMAWMY), first based on the titles and abstracts, after removing the duplicates. If there was insufficient information in the title and abstracts, the full texts were retrieved and reviewed to determine the study's eligibility. Any disagreements were discussed with a senior researcher (DG) and professor (AS). The two reviewers independently conducted full-text assessments based on the predefined inclusion and exclusion criteria. Both reviewers cross-checked the included papers and any disagreements were discussed, and resolved, with the senior researcher and professor.

Quality assessment
The quality of the studies was assessed using 14 items from the National Institutes for Health (NIH) Study Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies [22]. These covered the study power, the strength of the causality in the association between exposure and outcomes and the risks of potential selection bias, information bias, measurement bias or confounding bias. Studies were then categorized as good, fair or poor quality and reported using the total score for each study (Table S2 in the Supplementary Appendix).

Data extraction and synthesis
We then extracted the relevant data and placed them into an Excel spreadsheet, version 16.43 (Microsoft Corp, Redmond, WA, USA). These included the author, country, study design, sample, informants, age, sampling methods and response rates. We also extracted the pre-pandemic and pandemic timepoints, mental health outcomes and measures, the descriptive data before and during the pandemic and the inferential analysis results. The key findings were extracted and the changes to mental health were divided according to each outcome into three categories that showed whether the subject's mental health had deteriorated, improved or showed no difference. Where available, we also extracted information on the influence on gender, age and existing poor mental health problems and whether these were significant factors in the association to mental health before and during the pandemic.

Study selection and retrieval processes
The electronic and manual searches identified 2675 citations. A total of 575 duplicates were removed and the other 2100 records were screened for eligibility. Following the title and abstract screening, 1969 records were excluded and the full texts of 131 papers were evaluated. We excluded 110 full texts because they did not compare before and during COVID-19 pandemic timepoints, they did not provide specific data for individuals aged 0-24, used different measure before and during pandemic timepoints, focus on clinical samples or were based on administrative data. At the end of this process, 21 studies were included in the qualitative synthesis. Figure 1 shows the PRISMA flow diagram for the screening and study selection processes.

Changes in mental health before and during the COVID-19 pandemic
Most of the studies reported that mental health deteriorated during the COVID-19 pandemic. The findings are summarized in Fig. 2. Increased depressive symptoms were reported by eight studies [8,25,26,30,33,35,39,41], while one study each reported improve depressive symptoms [23] or no significant difference [7] after the pandemic started. Increased anxiety were reported by eight studies [7,8,25,30,[32][33][34]39] while one study found no significant difference [35]. Increased psychological distress was found by all four studies [24,[27][28][29]. Increased in stress or emotional stress were found in two studies [30,38], while one study reported no difference in physiological and behavioral stress [38]. Decreased mental wellbeing was reported by two studies [40,41]. Two studies reported increased in loneliness [8,24]. Increases in the negative affect was found in two studies [31,36], while decreases in positive affects was found in one study [36] and no significant decrease in positive affect in the other study [31].
Mental health change findings for those aged 10-24 years consistently pointed to the deterioration of mental health. We used the World Health Organization  definition of children and young people which include adolescents although we noted the arbitrary upper age limit used in some previous studies. The five studies that included children below 10 years old showed varying pattern and mental health outcomes. Out of the 21 included studies, the only study reporting improvement in mental health (depression) symptoms during the pandemic, was a study in China on school children aged 6-17 years [23].
Another study from the UK on those aged 7-12 years found depression symptoms worsened but reported no significant changes for anxiety symptoms and emotional problems [35]. Increased inattention and hyperactivity/ impulsivity were found in a study in Canada on young children aged 4-6 years [37]. A repeated cross-sectional study in Germany on children and adolescents aged 7-17 years reported significantly lower health-related quality of life, higher conduct problems, hyperactivity and peer problems during the pandemic, although no significant change for emotional symptoms was reported [7]. A longitudinal study in Italy reported significant deterioration in attentional problems, emotional regulation, hyperactivity, and willingness to study among primary school children aged 6-11.1 years. While similar changes were not shown in any of the outcomes among preschool children aged 3.2-6.2 years [26]. There were few studies assessed the significant influence of of age, gender differences and existing poor mental health when it came to mental health differences before and during the COVID-19 pandemic. Five studies found that mental health symptoms had worsened more in girls than boys [27,32,33,39,41]. In contrast, one study based on parental reports on adolescents aged 7-17 reported higher increases in mental health problems among boys than girls, in particular in externalizing problems including conduct problems, hyperactivity and peer problems [7]. Two of the largest studies in this review that focused on subjects aged 13-18 [41] and 11-20 [33] years found that mental health problems increased more in older than younger participants during the pandemic. Four studies that looked at subjects aged 16-24 years [27,40] and 18-24 years [24,28] compared to subjects older than 24 years old reported higher self-reported psychological distress [24,27,28] and higher decreased in mental well-being [40] in these age groups.
Three studies found greater effects in those who already had poor mental health before the COVID-19 pandemic [8,27,28]. Young women aged 16-24 who already had poor mental health in the pre-pandemic period, recorded increasing severe problem from 17.7% to 35.2% during the pandemic [27]. Another study showed the steepest increase in the proportion of clinically significant psychological distress in 2020, compared to 2014-2019, among female aged 16-24, the age group with already the highest proportions before the pandemic [28]. One study also showed depressive symptoms before the pandemic were a strong indicator of depressive symptoms among subjects aged 14-17 years during the pandemic [8]. Notably, one study of subjects aged  7-17 years reported that decreases in mental health were most significant in families with low socioeconomic status, migration background and limited living space [7].

Discussion
To our knowledge, this was the first systematic review to focus on collecting empirical evidence on studies focusing on children and young people aged 0-24 to assess changes in mental health symptoms before and during the COVID-19 pandemic. The studies included more than 96,000 subjects up to 24 years of age before and during the COVID-19 pandemic. Our systematic review of 21 studies from 11 countries had four main findings. First, most of the 21 studies reported a longitudinal deterioration in symptoms for different mental health outcomes especially for adolescents and young people. Second, the overall picture that emerged was that the mental health changes for younger children aged 0-9 years and the influence of gender, age and existing mental issues was limited in our included studies. Third, there was a very limited number of large-scale, repeated crosssectional designs with clear sampling frames. Fourth, there were also no cross-cultural studies identified that compared how different policies, namely lockdowns, school closures and other social restrictions, may have affected the mental health of the children and young people. We found that the 21 studies included 23 measures of anxiety, depression or psychological distress and that 20/23 (87%) showed increased levels. There was also some evidence of deteriorated negative affect, mental well-being and increased loneliness during the pandemic. Our review extended the findings from four previous reviews that were largely based on cross-sectional studies [10][11][12][13] that showed mental health of children and adolescents may have worsened during the current pandemic. Our findings of deteriorating mental health have global significance, because of the potential long-lasting consequences for the well-being of individuals, families and societies. Numerous birth cohort studies have showed that poor mental health in childhood predicted future mortality and morbidity [42,43]. In addition, childhood mental health problems have been associated with lower socioeconomic status and less stable social relationships in adulthood [44]. Our previous systematic review showed decreased mental health service use before and during the pandemic in subjects aged 0-24 years during the early phase of COVID-19 pandemic [21]. These two contradictory findings, of increased mental health problems but decreased service use during the early pandemic, indicated unmet needs.
The papers covered by the current review were all based on observational studies and any explanations for why mental health problems increased are largely lacking. Majority of the included studies collected during pandemic data at a very early stage of pandemic, when the more stringent restrictions were largely being implemented globally. A recent longitudinal study on adult population in 15 countries showed that more stringent COVID-19 policies throughout the first 15 month of the pandemic is linked to poorer mental health [45]. Thus, it's important to note that the present findings reflect the impact during the early phase of the pandemic on the mental health of children and young people. Other studies showed increased online or social media use [46,47] and problems related to remote learning [48,49]. These factors need to be explored, together with potential explanations like social isolation, family dysfunction, restricted leisure time activities, worries about being infected or about friends and family being infected and grief at losing loved ones.
Our systematic review showed that few studies have assessed the influence of demographic factors in association with the changes in mental health before and during the pandemic. Given that limited studies have assessed these factors and the variability of outcome in these studies, these results were inconclusive, but mainly in line with previous reviews [9,11,12]. Girls and older adolescents were associated with higher deteroriation in mental health symptoms during the pandemic. Mental health symptoms rose more strongly among female than their male peers and this may suggest that they might have been more vulnerable to the psychological effects of the pandemic. Depression and anxiety are increasing during puberty especially among girls [50,51], which may be one possible explanation for this gender differences. Of note, a previous review showed that the COVID-19 lockdown may have worsened eating disorders symptoms, which are much more common in female [52]. Also, subjects were significantly more affected if they had a pre-existing mental problem [8,27,28], low socioeconomic status, migration background and limited living space [7]. More robust research are needed to replicate these findings. This review has several implications for the methods that should be used by future studies. First, we only found a limited number of studies with large-scale, repeated crosssectional designs and clear sampling frames. Collishaw's criteria on time trend studies emphasize the need for comparable measures, clear sampling frames, convergent data by multiple informants and multiple data time points [14]. These kind of study designs are needed for future research, especially as the pandemic remains a global situation. It is possible that the psychological well-being of children and young people will be even more severely affected after longer exposure to the stressors associated with the pandemic. It has been argued that ongoing social isolation, family financial difficulties, missed milestones and school disruption, due to COVID 19 pandemic, will have cumulative adverse effects on the mental health of young people [11]. Second, there were no cross-cultural studies and these are needed to examine how different policies related to school closures and other restrictions have affected child mental health. Research that focuses on the impact of different policies will help societies to be more prepared to address new crises in a more effective and research-based way, such as future pandemics, threats of war and environmental catastrophes. Finally, rigorous studies that identify risk and resilience factors in children and young people during global crises are still lacking. These are urgently needed, so that effective health promotion and prevention strategies can be developed that maintain good mental health in challenging situations.

Strengths and limitations
The strengths of the study included the fact that the 21 papers we reviewed covered more than 96,000 children and young people aged from 3 to 24 years in 11 countries. These papers provided data on a range of mental health issues and indicated changes in mental health by comparing pre-pandemic and pandemic data. The review also had a number of limitations. We chose not to conduct a statistical meta-analysis, because of the heterogeneity of the study designs and mental health outcomes used by the studies we reviewed. In addition, only peer-reviewed papers published in English were included and we may have missed studies in other languages. Although 21 studies were included, only seven studies had a representative population-based dataset and we were unable to assess mental health on a larger scale. There was also lack of studies on children below 10 years old, limiting the interpretation that can be drawn for this age group. Finally, all the studies that we reviewed focused on changes during the early phase of the pandemic. Future research is needed to see whether subsequent waves had a different impact on the mental health of children and young people.

Conclusions
This systematic review of 21 peer-reviewed papers showed that the COVID-19 pandemic may have decreased the mental health of adolescents and young people in 11 countries. Future studies are needed to determine the long-term impact of the pandemic on their well-being especially on younger children. It is likely that the world will face similar threats in the future and that these could have an impact on mental health, including new pandemics, wars or environmental catastrophes. Therefore, research on how the COVID-19 pandemic, and different isolation, lockdowns and school closures policies, have affected families, children and young people in different countries, is vital if we are to build future sustainable societies.
Author contributions AS and DG obtained the funding and initiated the idea for the review article; LK and WMAWMY performed the literature search and screening; LK, WMAWMY, LL, KP and AS drafted the article; LK, WMAWMY, LL, KP, DG, KM, SG, KB, JB and AS critically revised the article.
Funding Open Access funding provided by University of Turku (UTU) including Turku University Central Hospital. This study was funded by the Academy of Finland via a COVID-19 grant (number 335690, PI Gyllenberg) and the INVEST-flagship (number 320162, PI Sourander), and by the Juho Vainio Foundation. The funders had no involvement in any aspect of the study or manuscript.

Data availability Not applicable.
Code availability (software application or custom code) Not applicable.

Conflict of interest
The authors declare that they have no conflict of interest.

Ethics approval (include appropriate approvals or waivers)
The manuscript does not contain clinical studies or patient data.
Informed consent (include appropriate statements, for example regarding "consent to participate" or "consent to publish") Not applicable.

Consent for publication Not applicable.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.