| Influenza, commonly known as the flu, is an acute respiratory illness caused by influenza viruses A and B (there's a third virus - C - but it is not harmful). It occurs all over the world and causes considerable morbidity and mortality each year (in the US alone, over 100,000 hospitalizations and 20,000 deaths each year).
The influenza virus is a complex, constantly changing virus. It is possible for someone who has already been infected with influenza to become re-infected in subsequent years.
There are two main types of influenza viruses of public health importance, namely influenza A and influenza B. A minor change in one or both strains of the virus may cause epidemics, because most people do not have enough antibody protection from past exposure to similar viruses.
Because of the changes in the influenza virus, immunity to flu is short-lived, and therefore large segments of the population are susceptible to influenza every year — though some are more at risk than others.
Influenza is a seasonal illness in temperate climates. The flu season in the temperate zones is during the winter months - November to March in the northern hemisphere, and May to September in the southern hemisphere.
Influenza A viruses infect several different animals including pigs, horses, other mammals, and aquatic birds as well as humans, whereas influenza B virus only infects humans.
A mild case of the flu may seem very much like a common cold. More often, the flu is associated with the sudden onset of headache, fever, chills, muscle aches, overall lousy feeling, cough and sore throat. These symptoms typically begin in such an abrupt fashion that people can recall the exact time that they got sick. In the majority of cases, people with the flu recover fully within one week. However, many people, particularly the elderly, develop persistent weakness after a case of the flu. This weakness can last for many weeks. It's important to understand the differences in symptoms between the flu and a cold, because a cold is a temporary bacterial infections, whereas the flu is a viral infection.
Persons 50 years of age and older should also receive the pneumococcal vaccine, which helps protect them against the most common type of bacterial pneumonia. These two vaccines can be given at the same time without increasing the risk of vaccine side effects. Unlike the flu vaccine, the pneumococcal vaccine should only be given once in a lifetime. Other high-risk candidates for the vaccine include: Residents of nursing homes and other chronic-care facilities, adults and children with chronic heart or lung disease, including asthma, adults and children who have required regular medical care or hospitalization during the preceding year because of a chronic illness, children and teenagers, age 6 months to 18 years, who are receiving long-term aspirin therapy, and pregnant women who will be in their second or third trimester of pregnancy during the influenza season.
Talk with your physician about questions you have regarding influenza and to schedule an appointment for your flu shot.
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