Read the excerpts from the opinion essay "On Immunity: An Inoculation" and the "Vaccination" informational text. Respond to the question. Which statement is best supported by evidence in both excerpts?

On Immunity: An Inoculation

Any given vaccine can fail to produce immunity in an individual, and some vaccines, like an influenza vaccine, are less effective than others. But when people are vaccinated with even a relatively ineffective vaccine, viruses have trouble moving from host to host and cease to spread, sparing both the unvaccinated and those in whom vaccination has not produced immunity.

Vaccination

The next step was to test whether the cowpox would now protect James from smallpox. On 1st July, Jenner variolated the boy. As Jenner anticipated, and undoubtedly to his great relief, James did not develop smallpox on this occasion nor on the many subsequent occasions when his immunity was tested again.

A) New vaccines tend to be highly effective for certain individuals when first produced.

B) It is impossible to spread diseases among individuals who have been immunized.

C) A vaccine can be effective simply by making it difficult for viruses to move among hosts. (Correct answer)

D) It is critical to test for immunity on multiple occasions to ensure that diseases don't spread to those without immunity.