A noted disadvantage of live attenuated vaccines?

• A. Interference from circulating antibodies
• B. They are heat-stable
• C. They are non-replicating
• D. They require no cold chain

Answer: (A)

Interference from circulating antibodies limits how well live attenuated vaccines work because these vaccines rely on the attenuated organism to replicate in the body and provoke a strong immune response. When antibodies are already present in the person—such as maternal antibodies passed to an infant, or antibodies from prior infection or vaccination—they can neutralize the vaccine strain before it can replicate. Without replication, there isn’t enough antigen exposure to fully prime the immune system, leading to a weaker or slower immune response and potentially reduced protection.

This is why timing matters for some vaccines: maternal antibodies wane over time, allowing the vaccine strain to replicate and stimulate immunity effectively.

Notes on the other statements: live attenuated vaccines are generally not heat-stable and require cold-chain storage; they do replicate in the host rather than being non-replicating; and they do not typically require no cold chain.