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ACT Science

ACT Science Question of the Day

Practice ACT Science with the production-style question-of-the-day selection for this public URL.

Question 1

Scientist 1

In any population wherein some individuals are susceptible to a given disease, the prevalence of that disease is as much determined by the fraction of the population that is immune as by other environmental factors. If the majority of members in a community are immune, even those who are still susceptible are afforded some degree of protection by herd immunity. The spread of disease is limited by the creation of a large immune population, which benefits the entire community. This is why it is so important to immunize as many people as possible against dangerous contagious diseases, as it protects not only those who have been immunized, but those who have not.

Scientist 2

It is true that immunizing individuals provides some protection against contagious diseases, but the value of "herd immunity" has been overblown. The threshold at which a large enough proportion of the population has been immunized so that contagions cannot spread—the herd immunity threshold—depends on the virulence of the particular disease, as well as the effectiveness of the vaccine and the parameters of contagion. It is much easier to immunize a population against a disease that is only spread through blood-to-blood contact than against one that is airborne; thus, the usefulness of the herd immunity phenomenon is so limited that it is basically negligible. Instead of focusing on immunizing some percentage of the population in the hopes of reaching the herd immunity threshold, we should increase our efforts to limit the spread of various diseases through proper hygiene procedures and limiting contact with high-risk sources.

Scientist 1 would most likely disagree with which of the following?

  1. All diseases have a relatively low herd immunity threshold.
  2. Environmental factors play a significant role in the prevalence of disease.
  3. The effectiveness of herd immunity depends on the proportion of the population that has been immunized.
  4. Non-contagious diseases, such as those caused purely by genetics, would not be preventable through herd immunity.
  5. The herd immunity threshold will always be over half of the individuals in the population
Explanation: Scientist 1 asserts that herd immunity can be an effective tool in controlling the spread of contagious diseases, but does not claim that all diseases have a low herd immunity threshold. Scientist 1 argues for herd immunity as a means of combatting contagious diseases. Non-contagious diseases, such as genetic disorders, will not be affected by herd immunity. Also, specific attributes of a certain disease may increase its virulence, leading to a high herd immunity threshold. Scientist 1 does not argue that all diseases will have low thresholds, and would likely disagree with this statement. The other answer options are all implied by Scientist 1's argument. He states that proportional immunity is as important "as other environmental factors" in determining overall prevalence, which suggests that environmental factors do play a significant role. He also states that "a majority" of a population would need to be immunized in order to achieve herd immunity; thus, any herd immunity threshold would be over half of the population.