A coronavirus-related pneumonia outbreak in Wuhan, Hubei province, in December 2019 has quickly expanded throughout China (Peng et al., 2020). This epidemic spread so quickly throughout the world. The Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) was the cause of the COVID-19 outbreak, often referred to as Coronavirus Disease 2019. The pandemic caused by SARS-CoV-2 was deemed a Public Health Emergency of International Concern by the World Health Organization on January 30, 2020. According to BKKBN, 2011, the population in Indonesia in 2010 had a total population of 237.6 million, of which 26.67% were teenagers (Shabrina & Nursasi, 2018)). An estimated 42,061.2 million persons, or 16.5% of Indonesia's total population, are between the ages of 15 and 24, according to data from the 2015 Inter-Census Population Survey. (Andriani et al., 2021).

Numerous initiatives have been taken to stop COVID-19 from spreading, including social distancing, staying at home, closing schools and online learning, limiting various types of extracurricular activities, making adolescents experience social isolation from friends and family for a long period (Houghton et al., 2022). This situation can make individuals lose togetherness with friends, causing boredom and loss of enthusiasm and joy. In addition, several studies have confirmed that teenage despair and anxiety have increased as a result of the COVID-19 epidemic, along with mental health and anxiety disorders ((Cost et al., 2022); (Avila et al., 2020)). Existing research shows that disasters or disease outbreaks that occur can pose a significant risk of mental illness in adolescents, especially loneliness and social isolation (Cénat et al., 2021).

Loneliness is a set of negative emotional states that individuals feel when they feel the difference, or unfavorable conditions between the desired thing and the reality that is happening (Cacioppo et al., 2006). Feelings of loneliness are feelings experienced by a person because genuine social interactions in life differ from one's desires (Domènech-Abella et al., 2017). Loneliness is seen as a severe problem for adolescents. Prior research has indicated that during the COVID-19 pandemic, adolescents experienced a higher prevalence of loneliness than adults did (Barreto et al., 2021)(Wang et al., 2020). According to (Labrague et al., 2021), the COVID-19 epidemic enhanced the incidence of loneliness symptoms among students in the Central Philippines. Approximately 56.7% of students are experiencing moderate loneliness, and 23.6% of other students are experiencing severe loneliness. This study also found that the protective factors for loneliness were social support, resilience, and coping behaviors.

Loneliness is one of the many problems that are easily found in adolescents but do not get serious attention. The impact of loneliness could not be taken lightly. Improperly managed loneliness increases the risk of mental illness and lowers the quality of sleep. (Kokou-Kpolou et al., 2020). Previous research has revealed that adolescents have greater problems, such as higher levels of loneliness, vulnerability to depression, anxiety, and suicidal ideation (Goossens et al., 2014). Further, other studies reported a relationship between loneliness to various physical problems, including hypertension, stroke (Valtorta et al., 2016), headache, insomnia, and fatigue (Majumdar et al., 2020).

Loneliness can affect all aspects of life, so knowledge about the factors contributing to loneliness is required. Existing research has confirmed various factors related to loneliness, including age (Luhmann & Hawkley, 2016), gender (Nicolaisen et al., 2014), and race/ethnicity (Wu et al., 2015). While many studies have confirmed the relationship between loneliness, they are still limited in examining the factors of loneliness.

Resilience is how individuals have positive psychological mechanisms to adapt and survive (Thomas & Revell, 2016). Resilience focuses on the individual's ability from the initial focus on the problem to how the individual empowers his strength to deal with problems in difficult times to achieve personal growth, such as disaster situations and disease outbreaks (Fu Keung Wong & Song, 2008). Resilience in adolescents can be interpreted as how adolescents can see various life difficulties experienced previously as a life lesson to get back up (Zulu, 2019). Resilience is considered important to overcome various problems due to home confinement (Holmes et al., 2020). In actuality, COVID-19 presents severe hazards to adolescents that require them to find the resources to deal with complex problems (Marchini et al., 2021). According to a previous Indian study, during the COVID-19 pandemic, over 45% of respondents felt extremely alone and unresilien (Lahiri et al., 2021). Growing research indicates that adolescents with higher resilience levels experienced less loneliness. (Falguera et al., 2021). Studies looking at aspects related to loneliness in teenagers during the COVID-19 pandemic have not been extensively researched, even though many have reported findings on resilience to help adolescents reduce stress, anxiety, and depression throughout the pandemic. Thus, this study aimed to investigate the variables linked to loneliness in Indonesian teenage populations during the COVID-19 pandemic.

This cross-sectional study design was conducted among adolescents in Indonesia. A link to a Google Form published on social networking sites was used to conduct the poll on Facebook and WhatsApp, which social media sites are the easiest to use in Indonesia. Data collection in this study was carried out from August to December 2021.

The G Power program version 3.1 was utilized to calculate the sample size for the study. As a guide recruitment participant, we conducted a power analysis in this study at 90%. Finally, the researcher calculated the sample size using 90% power at the 5% significance level with an effect size of 0.15 and the design effect of non-probability sampling, yielding a sample was 459. The researcher expected a response rate of 22%, further calculating the total sample size as 459 + (28%x 459), which equals 590 participants. The number of samples in the study was 590 adolescents. Sampling in this study used convenience sampling, where the researcher selected a sample among the adolescent population by what the researcher wanted. The inclusion criteria in the selection of the research sample were (1) willing to be respondents; (2) adolescents aged 10-19 years; (3) having the ability to read and write; and (4) compos mentis awareness. Respondents with mental illnesses and those who were less cooperative were the exclusion criteria in this study.

Ethical approval was obtained from the Sekolah Tinggi Ilmu Kesehatan Indonesia Maju with reference no. 2304/Sket/Ka-Dept/RE/STIKIM/X/2021. This research adhered to all applicable ethical guidelines. The procedure of collecting data started once the ethics committee gave its approval. After being told about the study, each participant signed a consent form and gave their informed consent. Authors removed and did not include data from the analysis if a participant did not complete the questionnaire. In addition, if adolescents experience stress or anxiety while taking part in the study, they could drop out at any moment.

This current study is the first to determine the self-reported correlation of loneliness among adolescents in Indonesia amid the COVID-19 outbreak. In the present investigation, social activity limitations are crucial in light of the COVID-19 pandemic, at least when identifying loneliness-related characteristics. To this end, a hierarchical linear regression model was employed. Loneliness is a condition that cannot be separated from every aspect of life. Loneliness is a form of emotional problem that can be experienced by everyone, with different levels of lightweight between individuals (Jong-Gierveld, 2021). Previous research in the general population has shown that life stressors can affect loneliness (Hensley et al., 2012).

Our results are significant for some reasons. First, loneliness is a prevalent condition in teenagers. It is estimated that loneliness occurs around 6 to 11 weeks after the lockdown during the COVID-19 pandemic (Magis‐Weinberg et al., 2021). Second, our study confirms a noteworthy connection between resilience and loneliness in adolescents. Adolescents who have resilience are associated with a lower likelihood of experiencing loneliness. Finally, our research also proves the importance of sociodemographic correlation with loneliness, namely age and gender. Overall, our study demonstrates the importance of sociodemographics in identifying loneliness levels. According to our research, adolescent girls are more prone than boys to feel lonely. and those adolescents aged 16-19 years have a higher prevalence than adolescents aged 10-15 years. Conversely, previous research stated that men reported more loneliness than women (Barreto et al., 2021). The meanings of loneliness between women and men at a younger age are relatively the same, but experience different experiences and meanings in adolescence (Ebesutani et al., 2012). Loneliness in female adolescents is caused by low self-esteem and low social skills, while loneliness in male adolescents is caused by anxiety due to excessive sensitivity (Panayiotou et al., 2016). Other studies also reveal that adolescent girls generally get higher social support than boys. immune system function (Solmi et al., 2020).

Furthermore, loneliness in adolescents may increase the likelihood that they would start harmful behaviors as a coping mechanism, such as smoking, binge drinking, overeating, or restricting their diet. These behaviors are risk factors that are strongly linked to mental health issues (Bolzetta et al., 2019). Before the covid 19 pandemic, adolescents in Indonesia spent a lot of time interacting with teachers and friends at school with learning and extracurricular activities, and they also had a lot of space to interact with many people with many facilities for social and recreational activities such as playgrounds and shopping places. The number of those stimuli becomes an obstacle to the loneliness felt by adolescents. Meanwhile, as an effort to stop the COVID-19 virus, it has influenced closing schools and limiting the social contacts of other teenagers outside the immediate nuclear family. This condition may cause a decrease in social contact and a high rate of loneliness in adolescents during the Covid-19 pandemic (Cooper et al., 2021). In a 2021 study, Leodoro et al. highlighted the value of having adequate emotional support from friends and family during trying times. They can provide people with tools to get over feelings of loneliness brought on by social isolation and lockdowns (Falguera et al., 2021). Therefore, adolescents during the pandemic may be more susceptible to loneliness, and the risk factors for loneliness during the COVID-19 pandemic may differ from adolescents before the COVID-19 pandemic.

The fact that respondents' adolescent characteristics are accurately represented in Indonesia makes this study strong. Self-reported questionnaires were used in this study, which constituted a restriction. Certain behaviors were either over-or under-reported.

In this cross-sectional research, we discovered that the frequency of loneliness among adolescents in Indonesia was 45.9%. During the Covid-19 pandemic, 63.7% of teenagers showed resilience. Teenagers between the ages of 16 and 19; female adolescents; confidence in one's gut feelings; tolerance for bad emotions and the intensifying effects of stress; and spiritual influence were all linked to an increase in adolescent loneliness. A reduced risk of loneliness was linked to positive acceptance of change, stable relationships, and control. The present findings, particularly the identification of contributing variables, should help create loneliness-prevention programs.