Why is a pathogen less likely to spread if most of the population are vaccinated?

Why is a pathogen less likely to spread if most of the population are vaccinated?

• A. It is less likely to come into contact with somebody who isn't immune.
• B. Vaccination makes it harder for the disease to spread overall.
• C. Vaccination eliminates all pathogens from the environment.
• D. Vaccination has no effect on transmission.

Answer: (A)

The key idea is herd immunity: when most people are vaccinated, there are far fewer susceptible individuals for the pathogen to infect, so transmission chains are broken more easily. An infected person is much more likely to encounter someone who is immune and cannot be infected or spread the disease, which makes the pathogen spread much less likely overall. That direct explanation is why the statement about being less likely to come into contact with someone who isn’t immune best captures how vaccination reduces spread. Vaccines don’t completely eliminate pathogens from the environment, and while vaccination can reduce transmission, saying it has no effect on transmission isn’t correct; nor does it simply “make it harder” without pointing to the reduced contact with susceptible people.

The key idea is herd immunity: when most people are vaccinated, there are far fewer susceptible individuals for the pathogen to infect, so transmission chains are broken more easily. An infected person is much more likely to encounter someone who is immune and cannot be infected or spread the disease, which makes the pathogen spread much less likely overall. That direct explanation is why the statement about being less likely to come into contact with someone who isn’t immune best captures how vaccination reduces spread. Vaccines don’t completely eliminate pathogens from the environment, and while vaccination can reduce transmission, saying it has no effect on transmission isn’t correct; nor does it simply “make it harder” without pointing to the reduced contact with susceptible people.