Introduction
Social isolation has been associated with poor sleep quality and mental health problems during the COVID-19 pandemic. However, most studies have investigated heterogeneous samples subjected to varying social distancing policies and did not focus on a single local profile subject to homogeneous prevention policies.

Objective
To evaluate the impact of the COVID-19 pandemic on mental health and sleep quality in a specific region in the South of Brazil where the populations have similar culture and local governments have adopted similar social distancing policies.

Methods
This study was conducted with 327 individuals aged 18-72 years, living in the Vale do Taquari area, Brazil. We assessed sociodemographic variables with a standardized protocol, symptoms of depression, anxiety, and stress with the Depression, Anxiety and Stress Scale-21 (DASS-21), sleep quality with the Pittsburgh Sleep Quality Index (PSQI), and post-traumatic stress symptoms with the Impact of Event Scale (IES-R), using a web-based online survey.

Results
Our results showed that sleep dysfunction moderated the effects of age on psychological symptoms, indicating that younger participants who had poorer sleep quality had worse mental health. Furthermore, participants with more perceived stress during the pandemic and more sleep dysfunction reported more symptoms of anxiety and post-traumatic stress.

Conclusion
Psychological symptoms were not related to social isolation duration but were related to the subjective perception that the pandemic interfered with life and generated stressful situations. These results may help governments make important decisions about protection and isolation measures in future waves of COVID-19 infection.