Influenza also called flu is an acute viral respiratory infection, transmitted by the influenza virus. This virus has three main types A, B and C. Influenza A is classified into different subtypes. The currently circulating seasonal viruses are Influenza A (H1N1), Influenza A (H3N2) and Influenza B viruses. The flu viruses are typically in circulation in the winter months in South Africa with an average start of the first week of June, although this varies.