Which of the following vaccine types requires replication to produce an immune response?

Live attenuated vaccines are designed to closely mimic a natural infection by containing a weakened form of the pathogen that can replicate in the host. This replication is essential because it allows the immune system to recognize and respond to the pathogen as if it were a real infection, leading to a robust and lasting immune response. The replication of the live attenuated strain stimulates both the humoral and cell-mediated immune pathways, promoting the production of antibodies and memory cells that provide immunity against future exposures to the actual disease.

In contrast, inactivated vaccines contain pathogens that have been killed or inactivated so they cannot replicate. These vaccines still elicit an immune response but do so without the additional replication factor involved with live attenuated vaccines. Toxoids are inactivated toxic compounds produced by pathogens and do not involve replication for immune response. Subunit vaccines contain only parts of the pathogen (like proteins) and also do not require replication to elicit an immune response.