Influenza or the flu is a common, infectious respiratory disease that begins in your nose and throat. It is highly contagious and can spread rapidly from person to person.
Human influenza, or the flu, is a respiratory infection caused by the influenza virus. Strains circulate every year, making people sick. Influenza typically starts with a headache, chills and cough, followed rapidly by fever, loss of appetite, muscle aches and fatigue, running nose, sneezing, watery eyes and throat irritation. Nausea, vomiting and diarrhea may also occur, especially in children.
Most people will recover from influenza within a week or ten days, but some - including those over 65 and adults and children with chronic conditions, such as diabetes and cancer - are at greater risk of more severe complications, such as pneumonia. Between 2 000 and 8 000 Canadians can die of influenza and its complications annually, depending on the severity of the season.
In Spring 2009, a new strain of the influenza virus, the H1N1 virus, was identified as causing influenza infections in people in North America. As the H1N1 Flu Virus spread around the world, the World Health Organization (WHO) declared it a pandemic influenza virus. As it was a new strain of influenza and because humans had little to no natural immunity to this virus, it caused serious and widespread illness.
On August 10, the World Health Organization (WHO) declared that the H1N1 pandemic had entered the post-pandemic period. This decision was informed by epidemiological evidence from around the world showing the H1N1 influenza virus was circulating at lower levels and behaving like a seasonal influenza virus.
Since the end of the 2009 H1N1 pandemic, the H1N1 influenza virus continues to circulate in Canada at low levels.
Birds and other animals, including pigs, also contract and transmit influenza. Wild birds, in particular, are natural carriers of influenza A viruses. They have carried animal influenza viruses, with no apparent harm, for centuries. Migratory waterfowl (ducks, geese) are known to carry viruses of the H5 and H7 strains or subtypes. These viruses are usually in the low pathogenic form - in other words, they aren't as deadly to birds as highly pathogenic strains.
The avian influenza H5N1 virus continues to cause sporadic human infections in a number of countries. There have been some instances of limited human-to-human transmissions among very close contacts. As reported by the World Health Organization (WHO), there has been no sustained human-to-human or community-level transmission identified thus far. The cumulative number of confirmed human cases of Avian Influenza A(H5N1) reported to WHO since 2003, as well as; confirmed Avian Influenza animal outbreaks, can be found at the Current Avian influenza (H5N1) affected areas.
People are exposed to different strains of the influenza virus many times during their lives. Even though the virus changes, their previous bouts of influenza may offer some protection against infection caused by a similar strain of the virus. However, three to four times each century, for unknown reasons, a radical change takes place in the influenza A virus causing a new strain to emerge.
To see where the flu is active in Canada, visit the FluWatch web site. FluWatch produces weekly influenza surveillance reports from October to May and bi-weekly reports from June to September each year.
Information on Emerging Respiratory Pathogens for both the public and public health professionals can be found on the Emerging Respiratory Pathogens page.
The National Advisory Committee on Immunization (NACI) provides the Public Health Agency of Canada with ongoing and timely medical, scientific, and public health advice relating to immunization. Past and present annual statements on Influenza vaccination can be accessed on the NACI web site.