Some other viruses cause these symptoms, and laboratory tests are required to determine the cause. Patients who have systemic symptoms as well as a cold and a cough are, therefore, described as having flu or flu-like illness. Most people recover within a few days, but some develop complications such as pneumonia. It is estimated about 2000 to 3000 people die each year as a result of flu. There are many different strains within each type of influenza virus.
Every year there are minor changes in the strains that are found in the population.
Some years, new strains appear, and some of these new strains may spread widely and cause epidemics in many countries. The World Health Organization monitors data on influenza viruses from laboratories in different countries, and makes recommendations about which strains should be included in vaccines. Routine vaccination against influenza virus Flu vaccines contain strains of influenza virus from each of the three the main groups. The strains that are included in the vaccine are changed each winter in order to protect people from the strains that are expected to occur that winter. These are people with chronic respiratory disease including asthma, chronic heart disease, chronic renal disease, diabetes mellitus, people who are immunocompromised through treatment or disease, people aged 65 years or over and people in long-stay residential homes.