Which Flu Is Worse, A or B?

Reviewed on 8/5/2022

Couple sick with the flu in bed
There are two main types of flu (influenza) virus, types A and B, and influenza A is often considered worse.

The flu (influenza) is a respiratory illness caused by influenza viruses transmitted from person to person through droplets propelled into the air when an infected person coughs or sneezes. The flu can cause mild to severe illness that can result in hospitalization or death. 

There are two main types of flu (influenza) virus, types A and B, that are responsible for seasonal flu epidemics (“flu season”) each year.

Influenza A is often considered worse. Influenza A viruses are:

  • More prevalent
    • Type A viruses are responsible for most cases (about 75%) of the flu 
  • Often cause more severe illness
    • However, a 2015 study found that both influenza types A and B had similar rates of illness and death
  • The only ones that cause flu pandemics, which are global epidemics of influenza
  • Constantly changing
  • Capable of infecting animals, commonly wild birds (influenza type B viruses can only infect humans)

What Are Symptoms of the Flu?

Symptoms of the flu (influenza) usually start within one to four days after exposure to the virus, and people may be contagious before even feeling sick. The flu is most contagious in the first three to four days after the illness begins and is generally considered contagious for at least a week after symptoms start. 

Flu symptoms usually come on suddenly. Symptoms of influenza A and B are similar and may include:

How Is the Flu Diagnosed?

The flu (influenza) is diagnosed based upon the patient’s reported symptoms and a physical examination, along with tests including:

  • Rapid influenza diagnostic tests (RIDTs) 
  • Rapid molecular assays 
  • Other specialized flu tests may be used in hospitals or state public health laboratories

What Is the Treatment the Flu?

The flu (influenza) is treated with home remedies and antiviral medicines in some cases. Influenzas A and B are treated the same way. 

Home remedies to help relieve symptoms of the flu include: 

  • Rest
  • Drink plenty of fluids
  • Inhale steam from a bowl of hot water or shower
  • Clean humidifier or cool mist vaporizer
  • Saline nasal spray or drops
  • Suck on lozenges 
    • Young children should not be given as they can be a choking hazard
  • Over-the-counter (OTC) medicines for symptom relief

Antiviral medications may be used to treat the flu but they work best when taken within 48 hours of the onset of symptoms to help reduce the severity and duration of the illness. 

Antiviral medications used to treat the flu include: 


Which illness is known as a viral upper respiratory tract infection? See Answer

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Reviewed on 8/5/2022

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