请判断并选择下面这段文字的写作逻辑：Millions have lost their lives to influenza in pandemics, and epidemics of varying severity occur worldwide each year. Strategies to prevent and control the often explosive outbreaks are limited to vaccination and treatment, if available, or to isolation and barrier precautions. Vaccination is considered the most important preventive measure, but there is a recognized need for additional control measures.