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COVID-19 and the impacts on youth mental health: emerging evidence from longitudinal studies

Several experts have warned that the current coronavirus disease 2019 (COVID-19) pandemic and associated confinement measures may have taken a devastating toll on youth mental health. While the COVID-19 pandemic has certainly created important challenges for children and youth, these claims vastly rely on cross-sectional data collected during the pandemic, from which it is difficult to draw firm conclusions. In this commentary, we offer a critical appraisal of the evidence from emerging longitudinal studies spanning the pre- and intra-pandemic period with a focus on internalizing and externalizing disorders, suicidality, eating disorders and substance use. We also discuss important research considerations in the monitoring of the long-term impacts of the COVID-19 pandemic on youth mental health as well as promising interventions to help mitigate potential long-lasting consequences of this unprecedented public health crisis.


Introduction
The coronavirus disease 2019  pandemic and associated confinement measures have created major disruptions in societal norms and public health infrastructure in Canada, and around the world. There is growing concern that social isolation resulting from these measures, combined with reduced access to mental health and support services within schools and community settings and fewer opportunities to engage in protective activities such as physical activity, may have detrimental short-and long-term effects on youth mental health and substance use (Marques de Miranda et al., 2020;Tsamakis et al., 2021). According to many experts, this constellation of factors in addition to the fear of contagion and other social and economic concerns has created a "perfect storm" that could precipitate the onset of mental health disorders among youth or lead to worsening of pre-existing ones. This may be particularly true among youth with pre-existing vulnerabilities such as being exposed to familial adversity (Cohen & Bosk, 2020;Jones et al., 2020).

State of the evidence on the mental health consequences of COVID-19 among youth
While evidence on the short-/medium-term impacts of COVID-19 on mental health has emerged for adults Ettman et al., 2020;O'Connor et al., 2020;Pierce et al., 2020), fewer studies have been conducted among children, adolescents and emerging adults, which represent three key developmental periods characterized by significant changes in mental health symptomatology (Jones, 2013). The few studies focusing on youth vastly rely on crosssectional information collected during the pandemic, from which it is difficult to draw firm conclusions due to the lack of comparison with pre-pandemic levels of symptoms. Only a handful of longitudinal studies with assessments of mental health before and during the pandemic are yet available. Nonetheless, certain observations can be made concerning specific mental health conditions and presentations.
Internalizing disorders (e.g., mood and anxiety disorders) Few longitudinal data, notably from the United Kingdom, suggest that depressive symptoms in youth may have increased during the early phases of the COVID-19 pandemic (compared with pre-pandemic levels), with some signs of recovery during the summer of 2020 (Barendse et al., 2021;Breaux et al., 2021;Newlove-Delgado et al., 2021;Pierce et al., 2020;Watkins-Martin et al., 2021). Though evidence is limited, worsening of mood symptoms during the early phases of the pandemic appears to have been associated with stricter lockdown measures (Barendse et al., 2021;Li et al., 2021). Evidence describing changes in anxiety symptoms appears more mixed, with sources indicating either improvements in symptoms, no change or minor detriments in early stages of the pandemic (Barendse et al., 2021;Bignardi et al., 2020;Watkins-Martin et al., 2021;Widnall et al., 2020). These results may reflect differential impacts in specific populations, for instance in youth with pre-existing mental health conditions (Breaux et al., 2021;Shanahan et al., 2020).
Externalizing disorders (e.g., conduct and attention-deficit hyperactivity disorders) A mixed-methods study conducted at the beginning of the pandemic highlighted increases in caregiver-reported externalizing symptoms, particularly tantrums, disobedience and attitude problems (Fitzpatrick et al., 2020). Similarly, a recent longitudinal study conducted in the United States among youth ages 7-15 years showed that increases in externalizing symptoms seen in many children were highly associated with lower levels of in-person/digital socialization and support from parents and peers (Rodman et al., 2021).
Suicide ideation, attempt and mortality While many experts have voiced their concerns about the impacts of the COVID-19 pandemic on suicide, such data are challenging to collect and evidence from longitudinal studies is only starting to emerge (John et al., 2020a;John et al., 2020b). Recent studies have reported no increase in the rates of death by suicide (Isumi et al., 2020;Leske et al., 2021). In terms of service utilization, evidence is mixed. One study reported a decrease in hospital presentations for self-harming behaviours (e.g., encompassing non-suicidal self-injuries and suicide attempts) in the first few months of the pandemic (Hawton et al., 2021), whereas others reported small increases in suicide ideation and attempts among youth presenting to a pediatric hospital (Hill et al., 2020) and those hospitalized for a psychiatric condition (Thompson et al., 2021).
Substance use Concerns around increased use of psychoactive substances as a coping mechanism for loneliness or mental distress have prompted investigations on youth substance use since the onset of the pandemic. The limited number of longitudinal studies available suggests that concern may not be warranted for all youth. Indeed, some report an initial decrease in alcohol and drug use at least in part due to fewer opportunities for social use (White et al., 2020). Other longitudinal studies suggest that while prevalence of youth tobacco, cannabis and alcohol use remained mostly stable during the first months of the COVID-19 pandemic, frequent and problematic use of substances increased in some higher-risk youth, such as those with concurrent mental health conditions (Bartel et al., 2020;Dumas et al., 2020;Naughton et al., 2021;Pinkham et al., 2020).

Eating disorders
In Canada and in other developed countries, specialized pediatric eating disorder programs have reported an unprecedented increase in the number of referrals and hospitalizations for restrictive eating disorders since the beginning of the pandemic (Haripersad et al., 2021;Solmi et al., 2021;Szklarski, 2021). Accordingly, studies have reported an increase in disordered eating symptomatology in the general population (Nutley et al., 2021) as well as adults and youth with pre-existing eating disorders (Castellini et al., 2020;Schlegl et al., 2020). At the time of writing, longitudinal research on eating disorders in the general youth population was still lacking from the peer-reviewed literature.

Monitoring the impacts of the COVID-19 pandemic on youth mental health
Evidence from longitudinal studies presents a complex and nuanced picture of the impacts of the COVID-19 pandemic on youth mental health with fluctuations associated with tightening of lockdown measures (including school closures) and differential effects among youth with risk and protective factors Viner et al., 2021). Given the rapidly evolving nature of the COVID-19 pandemic and numerous methodological challenges involved with identifying the mental health impact of the pandemic, an interdisciplinary research approach and follow-up of large population-based longitudinal cohorts with repeated assessments of mental health (ideally with baseline measures) will be key to understanding the long-term impacts of the pandemic . Examples of such already existing cohorts include the Canadian Healthy Infant Longitudinal Development Study (Takaro et al., 2015) and the Quebec Longitudinal Study of Child Development (Orri et al., 2021).
As the pandemic and post-pandemic period continues to unfold, it will be essential to monitor important markers of youth mental health, including symptoms of internalizing and externalizing disorders, disordered eating behaviours, suicidality and substance use behaviours. Combining observations from different cohorts could help examine a broad range of mental health indicators in specific age groups and in vulnerable population groups, which may be more severely affected by the pandemic. Administrative health records capturing medical service utilization (outpatient, emergency visit, hospitalization) for mental health reasons can also be used and linked to existing cohorts to monitor some of the impacts of the pandemic on youth mental health from a health services research lens. Another avenue can be to identify the intermediate pathways through which the pandemic can influence mental health, for example, studying the role of the loss of social connections on the likelihood of disordered eating symptoms among youth and across time. Finally, it will be crucial to consider impacts not only in representative, population-based samples but also in youth with existing vulnerabilities, including personal and family history of physical and mental illnesses as well as other genetic, developmental and environmental factors, as large studies may miss significant effects in specific subgroups.

Potential solutions
The widespread adoption of lockdown measures in the context of COVID-19 has created the necessity for a rapid adaptation of existing mental health treatment services, and in many settings, a shift towards digital health, including telehealth/telepractice (Raballo et al., 2020;Ramalho et al., 2020). Very little evidence is available to compare the long-term effectiveness of in-person and online services for youth mental health, and it is still unknown whether services delivered digitally may adequately serve the needs of all youth, or rather exacerbate existing inequalities among more vulnerable youth populations (Pellicano & Stears, 2020). Optimal integration of digital and traditional mental health services for high-risk populations is another area requiring additional research (Couturier et al., 2020). Nonetheless, services and care delivered virtually present a unique opportunity for increased access, especially for those living in areas in which access to in-person services may be limited (Rauschenberg et al., 2020). For example, a small number of pilot studies evaluating mindfulness, art therapy and philosophy interventions delivered virtually for children and adolescents have shown high levels of feasibility and promising preliminary results on youth well-being (Chadi et al., 2018;Malboeuf-Hurtubise et al., 2021a, b).
The use of new self-reported electronic screening tools delivered via technology in the context of the COVID-19 pandemic provides a promising avenue for improved early identification and intervention for mental health problems, but should be adapted from already existing selfadministered and provider-administered tools (Ransing et al., 2020). Combined with self-help resources such as mobile applications, online health communities and proper linkage with in-person or telehealth services, these can allow a full spectrum of interventions ranging from personalized care to population-based preventive measures that can be easily disseminated and brought to scale (Chew et al., 2020). For instance, the Climate Schools and PreVenture programs are two examples of promising universal and personalitytargeted interventions, delivered in-person or virtually, which have shown high levels of effectiveness in reducing the incidence of substance use and other mental health problems (Edalati & Conrod, 2019;Slade et al., 2021). Nonetheless, the use of innovative technological approaches and its integration with already existing in-person resources needs should be studied with care, to optimize both costeffectiveness and clinical efficacy.

Conclusion
In sum, more than one year after the adoption of wide-scale COVID-19 public health preventive measures, there is only limited longitudinal evidence on the impacts of the pandemic on child and youth mental health. Longitudinal findings paint a more nuanced picture than some cross-sectional studies from Introduction La pandémie de la maladie à coronavirus 2019 (COVID-19), et les mesures de confinement connexes, ont perturbé les normes de la société et les infrastructures de la santé publique au Canada et ailleurs. On s'inquiète à présent que la distanciation sociale et l'isolement qui s'en suit (y compris l'accès réduit aux services de santé mentale, au soutien psychologique en milieu scolaire et communautaire, et aux activités protectrices telles que l'activité physique) aient un effet dévastateur sur la santé mentale des jeunes. On craint pour l'usage des substances à court et à long terme (Marques de Miranda et al., 2020;Tsamakis et al., 2021). Nombreux experts appréhendent une « tempête par excellence » de troubles de santé mentale précipités et/ou aggravés par la pandémie, par la peur de la contagion, et par les problèmes socioéconomiques, en particulier chez les jeunes en situation vulnérable telle que l'adversité familiale (Cohen & Bosk, 2020;Jones et al., 2020).

Données probantes sur les conséquences de la COVID-19 sur la santé mentale des jeunes
Malgré les données émergeantes sur les impacts à court et à moyen terme de la COVID-19 sur la santé mentale des adultes Ettman et al., 2020;O'Connor et al., 2020;Pierce et al., 2020), il y a peu d'études à présent sur la santé mentale des enfants, des adolescents, et des jeunes adultes. Or, ces trois groupes représentent trois périodes clés du développement, périodes the early stages of the pandemic, though there is reason to believe that there could be long-term impacts on youth mental health, especially in more vulnerable youth. These findings build on numerous reports from clinicians suggesting significant increases in referrals and admissions for mental health problems, notably in relation to pediatric eating disorders (Furey, 2021;Haripersad et al., 2021;Solmi et al., 2021;Szklarski, 2021;Wilton, 2021). Considering that child and adolescent mental health services were already overstretched and underfunded before the onset of the pandemic, there is a pressing need for government investment to support and improve existing services as well as research on youth mental health (Malla et al., 2018). High-quality intervention research will be key to ensure optimal delivery of child and adolescent mental health services and mitigate potential long-lasting consequences of this unprecedented public health crisis.