The influenza virus can mutate or evolve in two different ways: antigenic drift and antigenic shift. The two are quite different and have much different results. Influenza mutates in both these ways so that it can bypass the human immune system. Just like every other living thing influenza mutates and evolves so that it can survive, if it didn’t mutate then the human immune system would recognise it and kill it and no new strains would form, causing the disease to eventually die out.
This makes trying to find a cure for Influenza very hard because it is always changing and there are so many different types of strains. If this was not the case then finding a cure would be a lot more simple.
Antigenic Drift
Antigenic drift is where the virus slowly changes its antigens or protein on the surface of itself. This gradually creates new strains of the disease until one evolves that can infect people who have become immune to strains that have already existed. The different antigens mean the immune system can’t recognise the new strains and so the viruses can infect the human. These new strains replace older strains and infects populations; often causing a seasonal influenza. Because the evolved strains are still quite similar to the older ones, some people will still be immune to them.
Because antigenic drift is quite gradual, scientists can predict the mutation using older strains and make a vaccine for some strains of seasonal influenza.
Antigenic drift is quite similar to how we humans evolve but much more rapidly. When influenza spreads through large populations of animals antigenic drift is sped up, so much so that it causes antigenic shift and ultimately a pandemic.
 |
| https://www.atrainceu.com/Courses.php?CourseID=33&page=1 |
Antigenic Shift
Antigenic shift mainly happens in large populations in livestock, particularly birds, where it can spread rapidly without resistance and evolve much quicker. In these situations the virus can mutate so much that it’s actual RNA can rearrange causing it’s antigens to be completely different. These completely new strains can then evolve so that they can infect humans. Because the new strain has completely new antigens we would have no resistance or immunity to it. This strain can then spread uncontrollably, causing a pandemic.
Eventually of course we develop immunity to this strain so it mutates and goes through antigenic drift and creates new strains repeating the cycle again.