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H3N2 Flu: Protection & Prevention for High-Risk Groups

Author: Public Health Agency of Canada
Published: 2014/12/29 - Updated: 2025/11/30
Publication Details: Peer-Reviewed, Instructive / Helpful
Category Topic: Influenza - Colds - Related Publications

Page Content: Synopsis - Introduction - Main - Insights, Updates

Synopsis: This information comes from the Public Health Agency of Canada, a government health authority, and addresses a serious respiratory illness that affects millions annually, with particular relevance to seniors and those with chronic conditions who face heightened complications. The guidance emphasizes that while H3N2 remains the dominant flu strain, the annual seasonal vaccine offers meaningful protection across multiple virus strains - even when a specific strain mutates, the vaccine still guards against the other viruses in its formulation. For elderly people, those in care facilities, and individuals with conditions like asthma or cardiac disorders, this practical breakdown of symptoms, risk factors, and prevention strategies (including vaccination timing and antiviral treatment options) provides actionable knowledge that can mean the difference between managing a routine illness and facing serious hospitalization - Disabled World (DW).

Definition: Influenza A Virus: Subtype H3N2

Influenza A virus subtype H3N2 is a subtype of viruses that causes influenza (flu). H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains. H3N2 is increasingly abundant in seasonal influenza. Both the H2N2 and H3N2 pandemic flu strains contained genes from avian influenza viruses. The new subtypes arose in pigs co-infected with avian and human viruses and were soon transferred to humans. Swine were considered the original "intermediate host" for influenza, because they supported re-assortment of divergent subtypes. However, other hosts appear capable of similar co-infection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible. H1N1 may have been transmitted directly from birds to humans (Belshe 2005). H3N2v is a variant of H3N2 influenza virus. When this virus occurs in pigs, it is called "swine influenza." The virus does not usually infect people or spread among people. It is very different from human seasonal H3N2 viruses.

Introduction

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.

Main Content

Symptoms of The Flu

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.

This medical illustration depicts the systemic effects of influenza across the human body, organized by anatomical region.
This medical illustration depicts the systemic effects of influenza across the human body, organized by anatomical region. At the top, the brain identifies central symptoms including headache. The nasopharynx area highlights respiratory symptoms of a runny or stuffy nose and sore throat with associated aches. Along the sides, the muscular and joint systems show extreme tiredness and aches respectively. The respiratory system in the chest displays coughing as a key symptom. The gastric system in the lower abdomen indicates vomiting as a potential complication. On the left side, a comprehensive list groups symptoms into categories: central (headache), systemic (high fever), muscular (extreme tiredness), and joints (aches), while the right side labels specific body regions affected by the illness. The illustration uses anatomical accuracy with color-coded organ systems to help viewers understand how influenza impacts multiple body systems simultaneously, making it clear that flu is not merely a respiratory illness but a whole-body infection affecting various physiological functions.

Who is Most at Risk?

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 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.

Insights, Analysis, and Developments

Editorial Note: The persistence of influenza as a public health concern underscores why vaccine literacy remains essential, especially for populations bearing disproportionate risk. While media coverage often focuses on novel pathogens, seasonal flu continues to claim thousands of lives annually in Canada alone - a sobering reminder that prevention strategies grounded in decades of research remain among our most effective public health interventions, even when viral mutation reduces ideal vaccine effectiveness in any given season - Disabled World (DW).

Attribution/Source(s): This peer reviewed publication was selected for publishing by the editors of Disabled World (DW) due to its relevance to the disability community. Originally authored by Public Health Agency of Canada and published on 2014/12/29, this content may have been edited for style, clarity, or brevity.

Related Publications

: Learn the key differences between cold and flu symptoms, how each virus spreads, and when to seek medical care. Practical guidance for managing viral illness.

: Statement by U.S. Food and Drug Administration Commissioner Scott Gottlieb, M.D. regarding preparations for the upcoming flu season and vaccinations.

: Number of people susceptible to contracting pertussis is slowly rising setting the stage for an increase in number of new cases, especially in seniors.

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APA: Public Health Agency of Canada. (2014, December 29 - Last revised: 2025, November 30). H3N2 Flu: Protection & Prevention for High-Risk Groups. Disabled World (DW). Retrieved February 3, 2026 from www.disabled-world.com/health/influenza/h3n2-flu.php
MLA: Public Health Agency of Canada. "H3N2 Flu: Protection & Prevention for High-Risk Groups." Disabled World (DW), 29 Dec. 2014, revised 30 Nov. 2025. Web. 3 Feb. 2026. <www.disabled-world.com/health/influenza/h3n2-flu.php>.
Chicago: Public Health Agency of Canada. "H3N2 Flu: Protection & Prevention for High-Risk Groups." Disabled World (DW). Last modified November 30, 2025. www.disabled-world.com/health/influenza/h3n2-flu.php.

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