What does the H and N stand for in flu names , and why are they numbered??
Although the World Health Organization requires several parameters to be met when naming flu viruses, the one we are most familiar with are the Hs and Ns that are used to identify specific strains of the influenza A virus.
There are 3 basic types of influenza; A, B and C. Influenza C is the least contagious with the mildest symptoms. Influenza B can make you just as sick as influenza A but is less contagious and has never been responsible for a worldwide pandemic. Influenza A by contrast has the highest infection rates and its symptoms are much more severe than its milder brethren.
Influenza A’s power lies in the creative way it uses the tools at its disposal. Using protein spikes on their surface, viruses stick to our healthy cells, pop them open and then dump their genes inside, tricking our cell machinery into reproducing for them. Influenza A viruses are particularly good at this as they can have an assortment of accessory spikes that allow them to crack the code of a variety of animal cells.
Hemagglutinin (H) & neuraminidase (N) are two of flu A’s favourite protein accessories (Though not the only ones) and just like human fashion accessories the H and the N can come in a variety of styles. Each virus has an H style (H1-H9) and an N style (N1-N16) and different combinations can allow them to invade the cells of different species.
Interestingly, influenza A viruses can also trade accessories with other viruses if they meet in a host through a process called reassortment. This is one of the reasons Influenza A can be so dangerous; a strain that could not previously infect humans can, under the right conditions, gain the ability much faster than we can respond to it.
Because of this, scientists must continuously modify vaccines to keep up with the abilities of this ever-altering quick-change combatant. Often they make educated predictions as to how a virus will mutate to produce a pre-emptive defense. So remember, when you get your flu shot this season it is not just a repeat vaccination. Instead, you are arming your body to defend against an invader who is carrying a different set of weapons than the flu ancestor you battled last year.