What Is Type B Flu Virus? Symptoms of Influenza Strain Spreading Across U.S.

This flu season medics have been struck by the uptick of cases involving the type B flu virus, which has been predominating the season for the first time in 27 years.

Influenza can be split into four different groups (A, B, C and D), each with a number of clades and subclades that differentiate the virus further. Influenza D affects cattle (not humans), while influenza A and B are responsible for the vast majority of illnesses each flu season.

Typically, influenza A dominates. Approximately three in every four cases of the flu that is confirmed is caused by an influenza A virus. However, this season, medics are reporting a resurgence in influenza B, which can be split into two families (B/Yamagata and B/Victoria).

According to the U.S. Centers for Disease Control (CDC), this is the first time influenza B has predominated in the U.S. since 1992-93.

Though it is typically less complicated than the influenza A virus, mutating less and triggering milder symptoms, it does seem to be particularly risky for children (especially those under five or with a chronic health condition), with studies showing higher pediatric mortality associated with influenza B than A.

According to CDC reports, there have been 32 pediatric deaths reported in the U.S. since the start of the season in fall—21 of which were caused by influenza B.

In total, the CDC estimates there have been around 4,800 to 12,000 deaths (and 87,000 to 150,000 hospitalizations) from the flu, since October 1, 2019.

The symptoms for influenza B (like other flu strains) include: fatigue; cough; fever (or chills); a sore throat; runny nose; muscle ache; headache; and gastrointestinal problems.

According to some research, the B virus might be more likely to involve headache, abdominal pain and myalgia (i.e. muscle pain) than other types.

Though most people should recover with rest and time (usually between a few days and a couple of weeks), there can be complications—such as pneumonia, organ failure, sinus and ear infections, and inflammation of the heart, even in otherwise healthy children.

According to the CDC, signs a child should receive urgent medical attention include: seizures; trouble breathing; a fever higher than 104 degrees Fahrenheit; bluish lips or face; chest pain; severe muscle pain; dehydration (i.e. no urine for 8 hours, no tears when crying and a dry mouth); the ribs pulling in with each breath; and not being alert or interacting when awake.

A worsening of chronic medical conditions (like asthma) or a fever or cough that improves but makes a comeback are also signs to take note of.

According the CDC, the best way to prevent the flu is via a vaccine: "CDC recommends that everyone 6 months of age and older get a seasonal flu vaccine each year by the end of October. However, as long as flu viruses are circulating, vaccination should continue throughout flu season, even in January or later."

The current batch protects against A/Brisbane, A/Kansas and B/Victoria.

Child with Cold
This season, medics have noticed a predominance of type B flu virus—a strain that can be particularly severe in children. Sasha_Suzi/iStock