Which statement about live attenuated vaccines is correct?

Which statement about live attenuated vaccines is correct?

• A. They cannot replicate in the host
• B. They require only one dose for lifelong immunity in all cases
• C. They mimic natural infection by replicating to induce immunity
• D. They are safe for all immunocompromised individuals

Answer: (C)

Live attenuated vaccines use weakened microbes that can still replicate in the vaccinated person. This replication makes the immune system respond as if a real infection occurred, engaging both antibody and T-cell responses and often producing strong, lasting immunity with fewer doses. That replication is the key: it drives a broad and durable immune response similar to natural infection.

The other ideas miss this essential point: they either claim no replication occurs, which is false; they claim one dose guarantees lifelong immunity in all people, which isn’t universally true; or they claim safety for all immunocompromised individuals, which is not the case because replication can pose risks in those with weakened immunity.