Answer:
The correct answer is option 4. herd immunities .
Step-by-step explanation:
When a person is immune to a certain disease, it means that this person is protected. Such person may have a natural immunity or may be immune because a vaccine has been injected.
The person who is not immune means that they are exposed to this disease, their body does not have natural immunity and they have not received any vaccines.
Herd immunity serves to protect these people. Herd or group immunity works in such a way that by vaccinating a part of the population, added to people who already have natural immunity, individuals who are not immune will be protected.
This works because if a large part of the population is immunized, the disease will not have the chance to spread in large numbers and it will be more difficult for it to reach the non-immunized individuals.
Therefore, the correct answer is herd immunities.