Flu cases are rising in Canada: How does influenza B differ from influenza A?

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Flu cases are rising across Canada, but unlike previous years, influenza B is the driving force behind the jump.

According to FluWatch, which reports confirmed influenza cases across Canada each week, there were 510 laboratory detections of the virus in week 13 of 2023.

As reported by CTV News, that number of cases is not unheard of for influenza in Canada. However, 364 of those cases were influenza B, while 146 were influenza A. Out of those detections, 71 per cent are classified as influenza B, which differs from last year's cases being predominantly influenza A.

In week 13's report, which covers March 26 to April 1, 2.4 per cent of tests came back positive for influenza, a slight rise from 0.8 per cent in week seven.

"This weekly increase is due to the increase in the percentage of tests positive for influenza B," the weekly report indicates.

According to last year's FluWatch from March 13 to April 16, there were 1,287 detected cases of influenza. Out of those, only four were classified as influenza B.

Week 13 has also seen 15 pediatric hospitalizations related to influenza, where all but one case was detected as influenza B.

Between Aug. 22 and April 1, FluWatch shows there have been 67,806 influenza detections, 97 per cent of which have been influenza A. But as influenza B cases rise, that could change.

What is influenza?

Better known as the "flu," influenza is a contagious infection of the nose, throat and lungs caused mostly by influenza A and B viruses.

Influenza A is categorized into sub-types based on two proteins, hemagglutinin (HA) and neuraminidase (NA). According to Health Canada, the most common subtypes to have affected humans include three subtypes of HA and two subtypes of NA, including H1N1, H5N1 and H2N2.

Influenza B, on the other hand, is only categorized into two lineages: B/Yamagata and B/Victoria.

Out of the two, influenza A is more common, typically spreads early in the season and can be spread between animals and humans. Influenza B usually shows up later in the season and can only be spread amongst humans.

However, the Centers for Disease Control and Prevention notes that influenza B can be more common and severe in children.

How dangerous is influenza?

According to Toronto Public Health, around 5 to 10 per cent of adults and 20 to 30 per cent of children are infected with influenza each year.

Health Canada indicates most people will recover from the virus within three to seven days, but severe illness can occur for some.

In Canada, influenza is ranked among the top 10 leading causes of death. According to data collected prior to the COVID-19 pandemic, influenza would cause around 12,200 hospitalizations and 3,500 deaths across the country each year.

Worldwide, seasonal influenza would cause one billion infections and lead to between 290,000 to 650,000 deaths, according to Health Canada.

Who's at risk of influzenza?

There are certain groups of people who are typically more at risk of catching influenza, including:

• Adults aged 65 and older

• Children younger than 60 months

• Pregnant people

• Residents of nursing homes and chronic care facilities

• Indigenous peoples

• People living in crowded conditions, or with barriers to accessing to health care

• People with chronic health conditions, like cardiac disorders, diabetes, lung disease, cancer and obesity

In Canada, people's risk of getting influenza is higher in the late fall and winter seasons.

What are the symptoms of influenza?

The most common symptoms of influenza include a fever, cough and muscle aches and pain. Those will typically appear one to four days after exposure to the virus.

On top of that, some people might experience:

• Headaches

• Chills

• Fatigue

• Loss of appetite

• Sore throat

• Runny or stuffy nose

• Nausea and vomiting

• Diarrhea

How do I treat influenza?

Most people who have influenza will not need medical treatment.

The best way to treat an infection is by staying home, resting and consuming liquids. The Ontario Ministry of Health and Long-Term Care also recommends people avoid caffeine, alcohol and tobacco. Instead, anyone infected with the virus should take warm baths, gargle with a glass of warm salt water and rest with a hot water bottle or heating pad.

In some cases, you might be prescribed medication by a health care practitioner if you're very sick or high risk. However, Health Canada notes over-the-counter cough and flu medicine should not be given to children younger than six-years-old, unless advised by a health care professional.

How can I prevent influenza?

The best way to prevent influenza is by getting a flu vaccine. Health Canada notes that you cannot get the flu from the vaccine.

On top of that, the virus is mainly spread by droplets when infected people cough, sneeze or talk. While less common, sometimes a person can contract influenza by touching a surface or object with the virus on it and then touching their face.

Therefore, it's important to properly wash your hands with soap and warm water, as well as clean and disinfect high-touch surfaces.

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