Influenza B, H3N2 & H1N1

  • Although most people call influenza “the flu,” there are actually many subtypes of the influenza virus and mutations occur all the time.
  • There are three main types of influenza: A, B and C. Influenza A and B cause outbreaks of seasonal flu, but influenza C does not.
  • Influenza A is the most common type of the virus and is further broken down into subtypes (such as H1N1) and individual strains.
  • Influenza B is less common but still causes outbreaks of seasonal flu. One or two strains of influenza B are included in the seasonal flu vaccine every year to protect people from the strain(s) that researchers believe are most likely to cause illness during the upcoming flu season.
  • The quadrivalent flu vaccine contains two strains of influenza B but the traditional trivalent flu vaccine only contains one. 
  • Influenza B is not broken down into subtypes like influenza A is, but it is broken down into individual strains.

Symptoms of Influenza B

  • Symptoms of influenza B are the same as the symptoms of other types of the flu.
  • Most people will experience symptoms such as coughing, fever, headache, body aches, exhaustion, and congestion.

  • H3N2 Flu is a subtype of influenza A.
  • Although they are multiple types of influenza, only influenza A is further broken down into subtypes.
  • These subtypes are actually broken down even further as they are identified by the World Health Organization.
  • When WHO officials choose the strains of influenza to include in the yearly flu vaccine, they choose two strains of influenza A (one variant of H1N1 and one variant of H3N2) and one or two strains of influenza B.
  • Most flu vaccines contain three strains of influenza but the quadrivalent vaccine and the nasal spray vaccine, Flu Mist, contain four (two strains of influenza B instead of one).
  • These strains are chosen over 6 months before flu season starts because it takes that long to manufacture and prepare those vaccines for distribution.


  • H1N1 flu is also known as swine flu. It’s called swine flu because in the past, the people who caught it had direct contact with pigs. That changed several years ago, when a new virus emerged that spread among people who hadn’t been near pigs.
  • Influenza A (H1N1) virus is the subtype of influenza A virus that was the most common cause of human influenza.
  • It is an orthomyxovirus that contains the glycoproteins haemagglutinin and neuraminidase. For this reason, they are described as H1N1, H1N2 etc. depending on the type of H or N antigens they express with metabolic synergy.
  • Haemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. Neuraminidase are a type of glycoside hydrolase enzyme which help to move the virus particles through the infected cell and assist in budding from the host cells.

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