Structure of the Influenza Virus
The genetic material (RNA) that is responsible for propagation of the virus is surrounded by a virus membrane comprising an envelope of lipids. This envelope contains proteins such as haemagglutinin (H) and neuraminidase (N), or so-called glycoprotein spikes. They allow the virus to attach to the host cell and the RNA to penetrate into the cell, as a result of which the virus can then reproduce in the host cell. These proteins fit the surface structures of the preferred host cells exactly. This explains the host specificity of the virus for, for example, birds, pigs or humans, i.e. why a certain species of animal or humans can or cannot become infected by it.
At the same time the glycoproteins are also antigens, against which the immune system of the host (animal or human) develops antibodies. Vaccines also contain these antigens and lead to the formation of antibodies after vaccination.
Epidemiology
Influenza viruses can change their genetic makeup very quickly (point mutation, antigenic drift). This results in new waves of flu epidemics. The vaccines therefore also have to be adjusted to these changes repeatedly to remain effective.
The most-feared change is the one that can occur when, for example, an avian influenza virus fuses with a human flu virus in a host cell simultaneously infected with both viruses (antigenic shift). This can result in viruses that spread very quickly, cause severe illness and can lead to the feared pandemics.
Classification of the influenza virus: Orthomyxoviridae family
