Leprosy is one of the oldest diseases affecting humanity and, despite being curable, still represents a significant challenge for global public health, especially in developing countries. Brazil, although it has advanced in disease control, still has the second highest number of cases worldwide, making leprosy an endemic disease of national importance.

To evaluate the epidemiological profile of leprosy in southern Brazil from 2015 to 2025.

Ecological epidemiological study developed with data on the number of new leprosy cases per year for each state in the South Region. Data were extracted from the Sistema de Informação de Agravos de Notificação (SINAN), available through the DATASUS (Departamento de Informática do Sistema Único de Saúde) platform. The main variable analyzed was the leprosy incidence rate, calculated as the number of annual new cases per 100,000 inhabitants.

Over the analyzed decade, southern Brazil showed a general downward trend in the number of reported leprosy cases. In 2015, 2,402 cases were recorded, corresponding to an incidence rate of 8.26 cases per 100,000 inhabitants. This number decreased progressively until 2019. However, the sharpest drop occurred in 2020, the first year of the pandemic, when the incidence rate fell to 4.90/100,000 inhabitants. In the post-pandemic years (2023–2024), there was a slight recovery trend in notifications, but without returning to pre-pandemic levels. Partial data for 2025 indicate a very low number, which is expected for data still under consolidation. The abrupt decline in 2020 and the slow subsequent recovery strongly indicate that the COVID-19 pandemic negatively impacted leprosy surveillance. There was a 27% reduction in the mean annual number of cases and a 29.4% reduction in the mean incidence rate during the pandemic period compared to the previous five years.

The epidemiological analysis of leprosy in southern Brazil from 2015 to 2025 shows a declining trend; however, this trend was drastically and artificially accentuated by the COVID-19 pandemic. The abrupt drop in notifications from 2020 onward is a strong sign of underreporting, posing a serious risk to disease control because it means there are undiagnosed and untreated people, keeping the chain of transmission active in the community.