We examined the association between social isolation and loneliness, increasingly recognised but neglected social determinants of health, with being unvaccinated against COVID-19.

This was a cross-sectional study.

A representative cohort of 22 756 individuals (aged 15–81 years) from the general Japanese population who responded to both the Japan COVID-19 and Society Internet Survey 2021 and Japan Society and New Tobacco Internet Survey 2022.

We calculated the ORs of remaining unvaccinated against COVID-19 in 2022, attributable to social isolation as assessed by the Lubben Social Network Scale, or loneliness as evaluated by the University of California, Los Angeles Loneliness Scale version 3. Reasons for abstaining from vaccination were solicited from the unvaccinated respondents. A multivariable logistic regression model was conducted with adjustments for demographic variables. Propensity score-matched comparisons were conducted as part of the sensitivity analysis.

Individuals with social isolation were more likely to be unvaccinated (OR 1.48, 95% CI 1.37 to 1.60), while individuals with loneliness were not (OR 0.96, 95% CI 0.88 to 1.05). Socially isolated individuals were significantly less likely to receive information from people who had been vaccinated (11% vs 15%) and less likely not to trust the vaccine approval process (19% vs 27%) compared with those who were not socially isolated.

Despite not harbouring negative perceptions of the vaccine, socially isolated individuals exhibited lower rates of COVID-19 vaccination. Socially isolated individuals are important targets to reach to increase the number of vaccinated individuals.