As Flu Season Begins, Reviewing Types of Influenza

2021-2022 flu rates are difficult to forecast due to covid safety precautions

By Jonny Lupsha, Current Events Writer

There are technically three types of influenza with varying pandemic potentials. One type affects both humans and animals, while the other two only affect humans. Flu season 2021 is underway.

Woman blowing her nose into a tissue outdoors
Generally, flu season starts in late fall, but its timing, length of time, and severity varies each year. Photo By stockfour / Shutterstock

Flu season can begin as early as October, though cases spike later in the year. Last year’s flu season saw remarkably fewer cases due to social distancing and mask-wearing brought on by the coronavirus pandemic. In 2021, more people are returning to the office and schools are back in session, though masking up and social distancing are still encouraged in most places. Therefore, flu spread for the remainder of the year is unpredictable.

However, much is known about the influenza virus itself. In his video series An Introduction to Infectious Diseases, Dr. Barry Fox, Clinical Professor of Infectious Disease at the University of Wisconsin School of Medicine and Public Health, said there are three types of flu.

The Orthomyxovirus Family

According to Dr. Fox, seasonal flus are caused by influenza types A and B.

“Influenza A can affect both humans and animals; it has the highest pandemic potential due to the possibility for mixing human and animal genes, leading to surface protein mutations,” he said. “Influenza B is a human virus only, has much less mutational capacity than type A, and has only one set of surface proteins, hence there’s only one species.”

However, with type B, there are variations of the structure of the virus which are caused by mutations. Virus mutations come from errors in the rapid copying of genetic information.

Finally, influenza C is a human flu that causes such a mild respiratory illness that it’s not often caused as an influenza illness. Dr. Fox also pointed out that it’s important to note that “neither Flu B nor C is associated with pandemics.”

“Influenza is an RNA virus in the Orthomyxovirus family,” he said. “Like all viruses, it can’t replicate by itself. It needs to take over the protein machinery of a living cell and reprogram the cell to create more virus particles, which usually results in cell death.”

Adaptive Change vs. Treatment

According to Dr. Fox, Type A flu is covered on its outer surface by two foreign protein spikes designated letters H and N. H is short for hemagglutinin and N is an abbreviation for neuraminidase. The H spike acts like a barb for the virus to attach itself to the outside of a host cell. Next, the membrane of the cell engulfs the virus.

The N spike helps the virus break out of its host cell when the time is right, cutting holes in the host cell to let the virus escape and infect other cells.

“Through a complicated series of maneuvers, including uncoating of the virus—where the RNA slips out of its viral coating—the virus tricks the host cell to let the viral RNA into the cell, and once this occurs, the virus is in control,” Dr. Fox said. “Within about 12 hours of hijacking the cell, the influenza virus can release up to one million new viruses. With such a rapid rate, there is a high possibility for genetic mutations.”

Two antiviral medications, amantadine and ramantadine, were effective for treating Type A influenza for several years. Both slowed virus replication. However, due to the high rates of viral mutation in Type A influenza, the flu virus developed a strain that was resistant to both medications to the extent that neither are used anymore.

Changes like these make the process of developing a highly effective flu treatment far more difficult, though antivirals that inhibit neuraminidase are still beneficial.

Edited by Angela Shoemaker, The Great Courses Daily

About Jonny Lupsha, News Writer 942 Articles
Jonny is a freelance writer and novelist who lives in Sterling, Virginia. He has written for The Great Courses since 2017 and enjoys studying the courses as much as writing about them. Contact Jonny at lupshaj@teachco.com