Why might inactivated vaccines require larger doses than attenuated vaccines?

Inactivated vaccines often require larger doses than attenuated vaccines because they are generally less effective at stimulating a robust immune response.

While attenuated vaccines consist of weakened microorganisms that closely mimic a natural infection—thereby triggering a strong, long-lasting immune response—inactivated vaccines contain organisms that have been killed or inactivated using heat or chemicals. Because these inactivated organisms cannot replicate or cause even a mild form of the disease, the resulting immune response is often less complete. Consequently, greater quantities of the vaccine are administered to ensure the body produces a sufficient level of antibodies to provide protection against the infectious agent.12