Commonly known as “flu”, a viral infection of the respiratory tract (air passages). Influenza is passed on by infected droplets from sneezes or coughs. It generally arises during the winter period, usually in small outbreaks but, every few years, in epidemics.
There are three types of influenza virus: A, B and C. A person who has had an attack caused by the type C virus requires antibodies that give immunity against type C for life. Infection with a strain of type A or B virus gives immunity only to that certain strain. Type A and type B viruses, however, are able to alter to produce new strains; type A has been the cause of pandemics (disease outbreaks affecting many people) in the past century. Sometimes, a different strain of influenza virus that primarily affects birds can also affect humans such as avian influenza.
Complications and symptoms
Types A and B give classic flu symptoms; headache, fever, muscle aches and weakness. Type C gives a mild illness that is unidentifiable from a common cold.
Flu often clears up within seven to ten days, although those affected can sometimes not feel completely recovered for another week or two. Unusually, however, it takes an extreme form, causing acute pneumonia that can be fatal within a day or two, even in normally healthy young adults.
Type B infections in children occasionally mimic appendicitis, and they have been implicated in Reye’s syndrome. In older people and those with heart or lung disease, influenza can be followed by a bacterial infection such as pneumonia or bronchitis.
Flu vaccines holding killed strains of types A and B virus currently available in circulation only have a 60-70% success rate. The immunity they give is only short lived and vaccination has to be repeated yearly. Influenza vaccination is recommended for those with chronic respiratory disease, chronic heart disease, chronic kidney disease, chronic liver disease, immunosuppression, diabetes and those over 65. Vaccination is also advised for those in long stay residential care and for health care professionals who have constant contact with susceptabe groups. The human influenza vaccines will not protect against avian influenza.