Pre-pandemic social isolation as a predictor of the adverse impact of the pandemic on self-rated health: A longitudinal COVID-19 study in Japan.

Many studies have found adverse effects of the coronavirus disease pandemic on health. Irrespective of being infected by the coronavirus, lockdowns and other measures to restrict mobility have worsened an individual's subjective health assessment. Unlike previous studies, this study examined how pre-pandemic social isolation (in the form of no interaction with others and having no social support) affected the impact of the pandemic on self-rated health in Japan. To this end, we estimated fixed-effects models using 4172 observations of 2086 individuals obtained from a three-wave Internet nationwide survey conducted in January/February 2019 and February 2020 (before the pandemic), in March 2021 (when the pandemic-related state of emergency was effective in four prefectures and just after it was lifted in six prefectures), and in October/November (a full month after the state of emergency was lifted in all prefectures). The state of emergency raised the probability of reporting poor health by 17.8 (95% confidence interval [CI]:1.9-33.8) percentage points among the participants who had not interacted with others before the pandemic, compared with only 0.7 (95% CI: -3.1-4.5) percentage points among other participants. Similar results were obtained in the absence of social support prior to the pandemic. In conclusion, pre-pandemic social isolation was detrimental to health, suggesting that policy measures are needed to avoid social isolation to increase the resilience of public health to external shocks.