Epidemiology of influenza B infection in the state of Rio Grande do Sul, Brazil, from 2003 to 2019.

Influenza B virus (IBV) causes respiratory tract infections with mild, moderate, or life-threatening symptoms. This study describes the epidemiology of IBV infection in Rio Grande do Sul (RS), Brazil, over 17 years. Nasopharyngeal samples were collected from outpatients presenting acute respiratory illness (ARI) between 2003 and 2019, and from inpatients with severe acute respiratory infection (SARI) from 2009 to 2019.