Which type of vaccine uses a pathogen that has been modified to reduce its strength?

The correct answer is based on the concept of an attenuated vaccine. Attenuated vaccines are created by modifying a pathogen to reduce its virulence while maintaining its ability to provoke an immune response. This means that the pathogen is not fully killed or inactivated, but rather altered in a way that it cannot cause disease in a healthy individual.

When administered, attenuated vaccines simulate an infection, prompting the immune system to respond and build immunity. Because the live, weakened pathogen can replicate to a limited degree, these types of vaccines often elicit a strong and long-lasting immune response. This can lead to the development of both humoral (antibody-mediated) and cellular (T-cell mediated) immunity.

Other types of vaccines, such as inactivated vaccines, use pathogens that have been completely killed or inactivated, rendering them incapable of causing disease but also generally eliciting a weaker immune response. Recombinant vaccines use pieces of the pathogen, such as proteins, to elicit an immune response without using the live pathogen itself. Live vaccines, while they may sound similar, refer broadly to any vaccine that contains a live pathogen, which may not necessarily be attenuated for safety in all instances.

Thus, the principle of modification leading to reduced strength in