How the Flu Virus, Vaccine, and Medications Work

by Marycela Barron, RDN, LD

The current news cycle is filled with stories on the coronavirus that originated in Wuhan, Hubei Province, China in late 2019 linked to an open-air seafood and animal market. The coronavirus has not been identified and currently there are four people in the US confirmed to be infected.

The influenza virus, or the flu, comes in four types: A, B, C, and D.

Humans are susceptible, or can get sick, from types A, B, and C. Type D affects cattle. Type C will cause the mildest of illnesses of the three types. Types A and B can both cause serious illness, but type A mutates more rapidly than B and can cause a pandemic flu outbreak. 

A pandemic outbreak is a worldwide epidemic. An epidemic illness is an outbreak of a disease that affects a greater number of people than usual over a greater distance than normal. As mentioned above, influenza type A has an ability to mutate and a pandemic occurs when a new and different type of influenza A emerges, infects people, and spreads rapidly.

The influenza A virus is named in an HxNy fashion. The ‘H’ comes from hemagglutinin, which there are 18 kinds, and the ‘N’ comes from neuraminidase, which there are 11 kinds. There are 198 combinations possible but only 138 combinations are currently found in nature according to the CDC. Out of those 131 combinations the most commonly found in humans are the H1N1 and H3N3 viruses.

Hemagglutinin is a glycoprotein, or a protein with a carbohydrate attached, that allows blood cells to clump together. On the virus surface, this glycoprotein allows the viral cell to bind with sialic acid on the surface of human cells. The viral cell needs this contact in order to invade the human cell in order, reproduce, and repackage the reproduced material into many more viral cells.

Neuraminidase is an enzyme, or a particle that breaks up protein, that acts on sialic acid. After the virus replicates within the cell and is repackaged as it grows out of the surface of the host cell. The new viral cell is attached to the host cell via sialic acid and this is where neuraminidase cleaves the bond and the viral cell is free to invade and infect other host cells.

The human immune system will recognize the patterns on the hemagglutinin and neuraminidase surface and create antibodies to these patterns. However, once the cell mutates this could cause changes to the patterns found on the surface of these particles and no longer recognized by the immune system thus leading to infection.

If someone is suspected of carrying the flu virus, a blood test will be administered. The blood test will be a hemagglutinin-inhibition test and a positive test will be indicated when red blood cells do not clump together.

The most common treatment for the flu are Tamiflu and Relenza, which prevent the release of new viral cells from human cells by inhibiting the action of neuraminidase. However, the best way to prevent the flu is by being vaccinated. The flu vaccine usually has one H1N1 molecule, one H3N2 molecule, and one to two influenza B types. Remember that the immune system will recognize the molecules as foreign, create antibodies against these patterns, and act against the virus if detected. For more information, please see your doctor.


  1. CDC. Types of Influenza Viruses. Accessed January 26, 2020. < >.
  2. Doucleff, Michaeleen. What’s in a Flu Name? H’s and N’s Tell A Tale. NPR. Published May 7, 2013. Accessed January 25, 2020. <… >.
  3. Rogers, Kara. Hemagglutinin. EncyclopÆdia Britannica.
  4. Rogers, Kara. Neuraminidase. EncyclopÆdia Britannica.