‘Tis the Season: the ABCs (and Ds) of Influenza

The North Dakota Department of Health is seeing low influenza activity for this time of year. To date, their data shows, they have recorded 107 cumulative flu cases. This time last year, NDDoH had already recorded 1,376 cases of influenza in the state. Health officials attribute the decrease in cases from previous years to the measures being taken to reduce the spread of COVID-19, like physical distancing, staying home and wearing masks. Currently, the group that has had the highest occurence of flu infection is those ages 40- 49, with 16 cases. That group is followed by those 60- 6 9 (14 cases), 10-19 (13 cases) and 20-29 (13 cases). According to NDDoH data, there have been 4 influenza deaths in the state this season.

Around 33% of North Dakota residents have been gotten the flu shot, and those who have not are encouraged to do so as soon as possible.

Last year, North Dakota saw something rather unusual at the start of the flu season. In the years before, the season commonly started with a surge of Influenza A cases, followed by a surge in Influenza B in February/ March. In the first week of December 2019, North Dakota had already seen hundreds of cases, and 85% of them were Influenza B. What’s the difference? Here’s a bit of a refresher

Types of Influenza The CDC classifies four different types of the influenza virus: A, B, C, and D. A and B are those which cause seasonal epidemics “flu season,” though A viruses are the only type known to cause national and global flu pandemics.

Influenza A

• found in many species, including humans, birds, and swine

• causes seasonal epidemics - “flu season”

• only virus type known to cause national/ global flu pandemics

• tends to mutate and replicate more rapidly than the others, causing many subtypes to emerge (EX: H1N1 (Spanish Flu outbreak in 1918 and Swine Flu in 2009); H2N2 (Asian Flu in 1957); H5N1 (Bird Flu in 2004)

Influenza B

• typically only found in humans (humans are natural hosts)

• less common strain

• on average, thought to be less severe infection than Influenza A (studies now find similar rates of illness and death in both A and B strains)

•protection by vaccination lasts longer for influenza B than A (A mutates more rapidly that B)

Influenza C

• mainly occurs in humans, but is also known to occur in dogs and pigs

• regarded as least serious type humans can get

•produces mild respiratory illness (but can be serious in children under 2)

Influenza D

• mainly found in cattle

• not known to infect or cause illness in humans

A vs B Contagiousness

Both are highly contagious. Experts observe that viruses are spread mainly by droplets from when infected individuals cough, sneeze or talk. These droplets, landing on/near peoples’ noses or mouths, as well as those that get inhaled by others, transmit the flu. Though it’s thought to occur less frequently, people can also contract the virus by touching a surface or object that has the flu virus on it and then touching their mouth, nose or even eyes.

A vs B Symptoms/ Treatment

Symptoms of both strains are the same: fever, muscle aches, fatigue, nausea/vomiting, headache, chills, sore throat, etc. Treatment for both is also the same, because they are both : viruses. Treatments in

From 1

clude antiviral prescriptions aiming to reduce the severity of symptoms until your body can

fight off the infection.

Because of Influenza A’s many subtypes and quick mutation, it has the ability to cause more severe symptoms and wider outbreaks than Influenza B.

During March 2019, the CDC issued a health advisory to keep hospitals on high alert that flu activity remained high, “with an increasing proportion of activity due to influenza A(H3N2) viruses…” In the advisory report, they warned that H3N2 subtypes might be associated with severe, even deadly disease in older adults, children and other high-risk patients. Influenza A(H3N2) had also been associated with more hospitaliza

tions and deaths in people 65 years and older than other Influenza A subtypes.

At that time, the CDC was observing that the A(H3N2) subtype that hospital patients presented with was “antigenically distinct” from that which that the flu vaccine defended against. That shows how incredibly efficient and speedy the virus is in mutating: from October 2018 to February/ March 2019, the H3N2 subtype was able to recognize the im

mune defenses that vaccinated individuals had to fight the flu — and the virus altered its genetics so it wasn’t affected by the vaccine. When the genetics changed, even those who had been vaccinated had little defense against this new subtype.

Another way Influenza A mutates and creates epidemics is the major genetic shift the virus undergoes when animals transmit the infection to humans. Because our immune systems vary from our animal friends, when the flu passes to us, it takes on a whole new form, meaning we have little to no defense against the new subtype.

Its ability to mutate causes Influenza A to account for a large percentage of flue infec

tions during the fall and winter months. Influenza B, on the other hand, is less common during the same time. A large reason is because B mutates more slowly. Most often, the strains of B that the vaccine protects against remain the same throughout the season, so those who have been vaccinated are protected longer from B than A.

Influenza type C infections generally cause mild illness and are not thought to cause human flu epidemics. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people.

The flu season, in its very beginning, could change at any moment, and health officials remind everyone that it’s never too late to get vaccinated.