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Seasonal Flu: H3N2 Influenza

  • Published: 2014-12-29 : Author: Public Health Agency of Canada : Contact:
  • Synopsis: H3N2 influenza is currently the most common strain of flu circulating in North America.

Main Document

"Influenza typically starts with a headache, chills and cough. Those are quickly followed by fever, loss of appetite, muscle aches and fatigue, running nose, sneezing, watery eyes and throat irritation."

Seasonal influenza (the flu) is a serious illness that infects millions of Canadians every year. It is a common infectious respiratory disease that begins in the nose and throat. It is highly contagious and can spread rapidly from person to person. Flu cases result in approximately 12,200 hospitalizations and, on average, 3,500 deaths in Canada each year.

So far this year, H3N2 influenza has been the most common strain circulating in North America. Seniors, those aged 65 and older, are usually the most affected by the H3 flu type.


Influenza typically starts with a headache, chills and cough. Those are quickly followed 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 have uncomplicated influenza and recover from the flu within a week or ten days, but some are at greater risk of developing more severe complications such as pneumonia.

Who is Most at Risk

Symptoms of influenza illustration
About This Image: Symptoms of influenza illustration
Some people are more likely to get seriously ill if they catch the flu, including:

How to Avoid Getting the Flu

The seasonal influenza vaccine is safe and effective and remains the best protection against influenza viruses. Everyone over the age of six months is encouraged to get the vaccine.

It is especially important for those who are more likely to get seriously ill or suffer complications if they catch the flu. Getting the flu shot every year is important because the vaccine is reformulated annually to protect against the most current strains of the virus expected to be circulating during flu season. This year's flu vaccines were designed to protect against specific influenza viruses and strains that were expected to make people sick this winter.

Flu viruses are constantly changing which is why a flu vaccine is needed each year. Flu vaccine is made up of the flu strains that research suggests will cause the most illness in the upcoming flu season. The influenza A H3N2 strain circulating this year appears to have changed compared to the strain chosen for this season's vaccine. However, the vaccine can still provide some protection and remains the best way to protect yourself and your loved ones from the flu.

It's also important to remember that the flu vaccine protects against three or four flu viruses (depending on the type of vaccine you receive), so even when there is a less than ideal match or lower effectiveness against one virus, the vaccine will protect against the remaining two or three viruses.

In addition to getting the flu shot, you can protect yourself and your family from infection during flu season by taking the following steps:

If you are elderly and at high-risk of complications or if you are severely ill with the flu, consult your health care professional regarding early treatment with antiviral drugs to help manage the illness. It is important that antiviral drugs be started as early as possible after you get sick.

Flu shots are also highly recommended for:

Canadians can keep track of their influenza immunizations with ImmunizeCA, an app that helps parents store and manage their families' vaccination records, easily access their provincial or territorial vaccination schedule as well as find timely and accurate information on the benefits of vaccination.

Similar Topics

1 : FDA Statement Regarding Efforts to Improve Effectiveness of Influenza Vaccines : U.S. Food and Drug Administration.
2 : New SARS-like Virus WIV1-CoV May Cause Outbreak in Humans : University of North Carolina at Chapel Hill.
3 : Influenza: Symptoms of Severe Sepsis and Septic Shock : Mayo Clinic.
4 : Seasonal Flu: H3N2 Influenza : Public Health Agency of Canada.
5 : First Case of Coronavirus (MERS) Reaches United States : U.S. Department of Health & Human Services.
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