Which of the following statements about herd immunity is true?

• A. When herd immunity occurs, unvaccinated people become resistant to a disease.
• B. Herd immunity is when enough people are vaccinated against a disease so that it cannot easily spread.
• C. Herd immunity for any disease always requires >95% of a population to be vaccinated.
• D. All of the above are true.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the concept of herd immunity. Herd immunity occurs when a significant portion of a population becomes immune to an infectious disease, either through vaccination or previous infections, reducing the likelihood of disease spread.
2. Step 2: Analyze the statement 'When herd immunity occurs, unvaccinated people become resistant to a disease.' This is not accurate because unvaccinated individuals do not develop resistance themselves; rather, they are indirectly protected because the disease has fewer opportunities to spread.
3. Step 3: Evaluate the statement 'Herd immunity is when enough people are vaccinated against a disease so that it cannot easily spread.' This correctly describes herd immunity, emphasizing the role of vaccination in preventing disease transmission.
4. Step 4: Consider the statement 'Herd immunity for any disease always requires >95% of a population to be vaccinated.' This is not universally true, as the required vaccination threshold depends on the disease's contagiousness, often measured by the basic reproduction number (R0).
5. Step 5: Conclude that the true statement is the one describing herd immunity as a situation where enough people are vaccinated to prevent easy spread of the disease, rather than the other options.