Exploring the association of social isolation and loneliness on the experience of COVID-19 infection and hospitalization in the Japanese population: the JACSIS study

Social isolation and loneliness have been long-standing public health concerns, and the coronavirus disease 2019 (COVID-19) pandemic has exacerbated these issues. Therefore, this study aimed to investigate the associations of social isolation and loneliness during the pandemic with experience of COVID-19 infection and hospitalization in the Japanese population. Data were sourced from the Japan COVID-19 and Society Internet Survey (JACSIS), a large-scale, web-based national survey of individuals aged 15-79. This study used JACSIS data from 2020 to 2022, representing the first and third years of the pandemic. Social isolation was measured by the frequency of direct and indirect contact with people other than co-residing family members. Loneliness was evaluated using the UCLA Loneliness Scale, while COVID-19 infection and hospitalization were self-reported. A total of 13,612 individuals were included, of whom 1.5% had experienced hospital admission due to COVID-19, and 9.3% were infected but not hospitalized. Social isolation was inversely associated with COVID-19 infection risk (odds ratio = 0.77; 95% confidence interval: 0.66-0.90), while a higher level of loneliness was related to hospitalization (odds ratio = 2.21; 95% confidence interval: 1.59-3.09). Sex-stratified analyses revealed stronger associations in men than women. This study highlights the complex relationship between psychosocial factors and infectious disease outcomes, underscoring the need for comprehensive approaches to address the multifaceted challenges posed by global health crises.