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Flu Cases Are Rising In Canada: How Does Influenza B Differ From Influenza A?
Fourteen of the 15 pediatric hospitalizations related to influenza in one week were caused by influenza B. (Photo via Getty Images)
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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.
The best way to prevent influenza is by getting the flu vaccine. (Photo via Getty Images)
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.
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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.
Influenza A is typically more common and started spreading earlier, but influenza B is more severe and common in children. (Photo via Getty Images)
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.
The most common symptoms of influenza include fever, cough and muscle aches and pain. (Photo via Getty Images)
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
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.
Health Canada notes that 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. (Photo via Getty Images)
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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Influenza Expert Assesses How Worried We Should Be About H5N1
The current outbreak of a highly contagious strain of H5N1 avian influenza has been called the worst in history. By January 2023, poultry farmers in the U.S. Had slaughtered almost 60 million birds infected or at risk of being infected with H5N1, with a similar number being culled in Europe while in Japan, farmers set out to kill more than 10 million chickens.
It is not just poultry and wild birds that are being infected. In Peru, nearly 3,500 sea lions died from the virus. Cases have also been reported in otters, wild dogs and foxes.
But this strain of H5N1 is not new. It was first identified in 1996 in farmed geese in Southern China and Hong Kong, where the following year, it jumped from birds to humans, infecting eighteen people, killing six. Since then, variants of the virus have infected more than 800 people around the world, with 240 from Southeast Asia and China, the most recent cases hailing from Anhui Province in China and Cambodia, where an 11-year-old girl died from the virus.
So why are public health officials on high alert this time? Influenza expert Professor Gavin Smith, director of the Emerging Infectious Diseases Program at Duke-NUS shares his insights.
H5N1 has been circulating for more than 20 years and there have been relatively few cases in humans. Why are public health officials keeping a close eye on this virus?Smith: H5N1 has a very high fatality rate in humans, so it has consistently been considered a top pandemic threat. Since 1996, H5N1 has been commonly found in poultry across Asia. Because of live-bird markets—where people can buy a chicken or duck and have it freshly slaughtered—there is a huge exposure of people, both shoppers and workers, to the virus. This has resulted in sporadic infections, and some limited human to human transmission in the past. So there is concern that given enough chances the virus could adapt to efficient spread in humans.
The World Health Organization has said the risk to humans of this virus is low, but they are now reassessing. What's changed?Smith: In the last few years, H5 viruses (not just H5N1 but other N subtypes) had become more widely spread in wild birds and poultry across the world. The virus was initially restricted to Asia, then found its way to Europe and Africa before finally crossing to North America, first in 2014, which quickly died out by 2015, and then again in 2022. Subsequently H5N1 viruses have been detected in South America.
This wider geographic spread has increased the exposure of humans and other mammal species, such as seals, to H5N1 infection. This naturally increases the chances that the virus could adapt to mammals and potentially humans. While there is no evidence for this at the moment, it is important that the situation is closely monitored.
What do we know about the recent cases in Cambodia? Is there any evidence that the virus is passing between people?Smith: There were only two confirmed cases in Cambodia, the daughter and father. There is no evidence that there was transmission between the pair, it could also have been from two independent infections from poultry.
Are you concerned that the virus may be evolving to spread more easily among humans?Smith: At this stage, no. There is no evidence for adaptation to efficient human transmission. But repeated infection of mammal species, including humans, always increases that risk.
Some experts say that the strains that have been spreading since 2020 may be causing less lethal illnesses in people. Is that true, and if so, what would that mean in terms of assessing the pandemic risk of this virus?Smith: This is very hard to assess, and I am personally not convinced either way. We are not even sure of the extent of human infection in many countries because surveillance is either not done or is insufficient. Regardless, even if the virus was less deadly than in the past, it would still cause a pandemic similar in severity to SARS-CoV-2.
The WHO has called for wider production of H5N1 flu vaccines. What other steps should countries be taking to prevent a possible outbreak?Smith: We need to develop smarter ways of controlling the virus in animals, primarily through vaccination. Vaccination in poultry won't prevent infection by H5N1 but it does reduce the overall amount of virus in the poultry population, which leads to less spillover into humans. This approach has been successfully used in many countries to prevent human infection. Because people mainly get infected from poultry, we should concentrate on reducing the amount of virus in live-bird markets and farms.
For instances when a spillover event spirals into a sustained outbreak, what can we do to have vaccines ready fast enough to avoid costly lockdowns?,
Smith: The development and testing of universal influenza A vaccines—that would protect against most known influenza subtypes (the H and N combinations)—has been ongoing for many years. Since the COVID-19 pandemic and the success of mRNA vaccines, work has also started on mRNA vaccines that would protect against both influenza A and B. If these efforts are successful, we would be in a position to rapidly roll out vaccination in the event of an influenza pandemic.
The FDA has just approved the first OTC home-based flu test, could that offer us an edge in surveillance of suspected human cases?Smith: Because this test kit does not distinguish between types of influenza A viruses, it would not be of much use.
Obviously, in a world still coming out of the COVID-19 pandemic, people are going to be very anxious about what might be next. Overall, how worried do you think people should be about this virus?Smith: We have been studying these viruses for more than 25 years, and we have vaccines for birds available and human vaccines have been tested. There is also a good track record of influenza vaccines being used in people and we also have influenza specific anti-viral medicines. So overall, we are in a better position than when SARS-CoV-2 emerged. COVID-19 has also left us better prepared. We are more vigilant and already taking steps to prepare for a possible pandemic.
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Flu Cases Are Ticking Up, What You Need To Know About Influenza B
As fears of a "tripledemic" die down, health officials say they are seeing an uptick of a particular strain of the flu: influenza B.
According to data from the Centers for Disease Control and Prevention, the percentage of tests that are positive for influenza B has increased from 0.12% the week ending Jan. 7 to 0.36% the week ending March 25.
Meanwhile, over the same period, the percentage of tests positive for influenza A -- the most common flu strain -- has declined from 8.58% to 0.58%.
MORE: Flu cases, hospitalizations, deaths continue to surge across US
Meanwhile, states are showing similar trends. In New York, as of the week ending March 25, of the 2,013 samples subtyped, 64.16% were identified as influenza B, state health department data shows.
Dr. John Brownstein, an epidemiologist and chief innovation officer at Boston Children's Hospital, told ABC News that it's not surprising to see an uptick of influenza B toward the end of the flu season.
Percentage of Positive Influenza Tests
CDC
However, due to few to no cases of influenza reported during the first two years of the COVID-19 pandemic, people may have forgotten how the flu normally behaves.
"We have to remember that, overall, we're returning to a somewhat normal respiratory virus season," said Brownstein, an ABC News contributor. "Influenza B is often later in the season. ... It's not a surprise at all that we're seeing flu B and, as part of our return to normal, we have to remember that flu still has an impact on population health."
Since the beginning of the year, hospital admissions for flu have been declining, from 12,883 the week ending Jan. 7 to 1,222 the week ending March 25.
Brownstein said the decline of other viruses as helped prevent hospitals from being overwhelmed but advised Americans to stay vigilant.
"Right now, the hospitals are benefiting from a little bit of a break," he said. "We do have more breathing room in our hospitals than we have in the past, and that's thankful, because that means that we can perform elective procedures, that means that our frontline health care workers are getting a little bit of a breather."
MORE: Flu cases, hospitalizations, deaths continue to surge across US
Brownstein added, "We still have COVID circulating, there's still other viruses that are still creating capacity challenges. A bad flu B peak could bring us right back to some of those capacity concerns."
There are four types of influenza -- A, B, C and D -- however, A and B are the most common and cause seasonal epidemics in people, what we refer to as "fu season."
However, flu activity across the U.S. Remains in the "low" category and there Is currently no evidence that influenza B is more dangerous or more worrisome than Influenza A or any other strain.
"It just highlights the fact that, we still need to be vigilant about respiratory viruses, to being vaccinated against flu is still important," said Brownstein.
According to the CDC's weekly flu vaccination dashboard, about 48.3% of U.S. Adults reported receiving a flu shot as of mid-February, higher than the 45.1% who reported doing so the same time last year.
Flu and coronavirus (COVID-19) vaccine signage is seen at a pharmacy in New York, Jan. 5, 2023.
Michael M. Santiago/Getty Images
Meanwhile, about 54.9% of all children in the U.S. Are currently vaccinated against flu by the end of March, about the same as March 2022.
The federal health agency said flu vaccines are still very effective at preventing hospitalization and death. Flu vaccines administered this season reduced the risk of influenza A-related hospitalization among children by nearly three quarters and among adults by nearly half, the CDC said.
Brownstein said while it's never too late for someone who hasn't gotten the flu vaccine yet to be immunized, there will be availability issues as pharmacies and doctors' offices give out their final doses.
"You will be challenged by availability and, of course, the longer you wait, the further the value of that vaccine is diminished," Brownstein said. "The value keeps going down the longer you wait."
ABC News' Emma Egan and Youri Benadjaoudi contributed to this report.
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