Disease and Natural Selection
One type of natural selection is called frequency-dependent selection. This type of selection favors phenotypes that are either common, positive frequency-dependent selection. or rare, negative frequency-dependent selection. An example of negative frequency-dependent selection can be observed in the interaction between the human immune system and various infectious agents such as bacteria or viruses. As a human population is infected by a common strain of bacteria or virus, the majority of individuals in the population become immune to it, either naturally or through the use of antibiotics and/or vaccinations. This then selects for rarer strains of the bacteria or virus. which can still infect the population because of mutations. The new strains have greater evolutionary fitness because they are less common.
The CDC recommends a yearly flu vaccine as the most important step in protecting against influenza and its potentially serious complications. The seasonal flu vaccine protects against the three or four influenza viruses that research indicates will be most common during the upcoming season. If you do get a flu shot, you can still possibly get the flu. Using the illustration and prompt, explain how this can happen. All BUT ONE choice could apply.
Responses
A Variation in the influenza virus population always exists.Variation in the influenza virus population always exists.
B The influenza virus mutates rapidly, from season to season.The influenza virus mutates rapidly, from season to season.
C Once subjected to the vaccine, the virus begins to evolve and become resistant.Once subjected to the vaccine, the virus begins to evolve and become resistant.
D You are exposed to an influenza virus that was not included in the seasonal vaccine
C Once subjected to the vaccine, the virus begins to evolve and become resistant.
This is the most likely explanation for still getting the flu after receiving a flu shot. The influenza virus can mutate and evolve rapidly, potentially becoming resistant to the vaccine strains. This is why a new flu vaccine is needed each year to keep up with the changing virus.