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.

Who is Most at Risk?
Some people are more likely to get seriously ill if they catch the flu, including:
- Aboriginal Peoples.
- People 65 years of age and older.
- Healthy children 6 months to 5 years of age.
- Healthy pregnant women, at any stage of pregnancy.
- Residents of nursing homes and other chronic care facilities.
- Children and adults (including pregnant women) with chronic medical conditions, such as cancer, cardiac disorders, asthma, and morbid obesity (people with a body mass index greater than 40).
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:
- Clean hands frequently.
- If you get sick, stay home.
- Keep your hands away from your face.
- Eat healthy foods and stay physically active to keep your immune system strong.
- Keep common surface areas - for example, doorknobs, light switches, telephones and keyboards - clean and disinfected.
- Cough and sneeze into your arm, not your hand. If you use a tissue, dispose of it as soon as possible and wash your hands.
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:
- People in direct contact during culling operations with poultry infected with avian influenza.
- Those who provide services within closed or relatively closed environments to persons at high risk (e.g. crew on a ship).
- People who provide essential community services including emergency medical responders such as paramedics, police and firefighters.
- Those in close contact with individuals at high-risk for complications (e.g. healthcare workers, household members, and those providing childcare to children up to five years of age).
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.