What is seasonal influenza? Seasonal influenza (or “flu”) is most often caused by type A or B influenza viruses. Symptoms include sudden onset of fever, cough (usually dry), headache, muscle and joint pain, sore throat and a runny nose. The cough can be severe and can last 2 or more weeks. Most people recover from fever and other symptoms within a week without requiring medical attention. However, influenza can cause severe illness or death in high-risk groups (see Who is most at risk? below). Seasonal epidemics occur mainly during winter, from October to March in the northern hemisphere and April to September in the southern hemisphere. In tropical and subtropical countries, seasonal influenza can happen all year round. How can I avoid getting the flu? The best way to avoid getting the flu is to get the flu vaccine every year. Influenza viruses evolve constantly, and twice a year WHO makes recommendations to update the vaccine compositions. For the 2016-2017 norther...