Department of Pediatrics, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran.
Nursing Research Center, Kerman University of Medical Sciences, Kerman, Iran.
Department of Medical Education, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
Influenza, commonly known as the flu, is an infectious disease caused by an influenza virus (1). Symptoms can be mild to severe (2). The most common symptoms include: high fever, runny nose, sore throat, muscle pains, headache, coughing, sneezing, and feeling tired (1). Three of the four types of influenza viruses affect people, Type A, Type B, and Type C (3, 4). Type D has not been known to infect people, but is believed to have the potential to do so (4, 5). Usually, the virus is spread through the air from coughs or sneezes (1). Influenza spreads around the world in yearly outbreaks, resulting in about three to five million cases of severe illness and about 250,000 to 500,000 deaths (1). About 20% of unvaccinated children, and 10% of unvaccinated adults are infected each year (6). In the northern and southern parts of the world, outbreaks occur mainly in the winter, while around the Equator, outbreaks may occur at any time of the year (1). Death occurs mostly in the young, the old, and those with other health problems (1). Larger outbreaks known as pandemics are less frequent (3). In the 20th century, three influenza pandemics occurred: Spanish influenzain 1918 (~50 million deaths), Asian influenza in 1957 (two million deaths), and Hong Kong influenza in 1968 (one million deaths) (7). The World Health Organization (WHO) declared an outbreak of a new type of influenza A (H1N1) to be a pandemic in June 2009 (8).