Which of the following is an example of a live attenuated vaccine?

A live attenuated vaccine contains a version of the living virus that has been weakened or attenuated so that it cannot cause disease in a healthy individual. The Measles, Mumps, and Rubella (MMR) vaccine is an example of this type of vaccine, as it contains live but weakened strains of the viruses that cause these diseases. This allows the immune system to mount a response without causing the actual diseases, thereby providing immunity and effectively training the body to recognize and fight these viruses in the future.

In contrast, the inactivated polio vaccine is made from viruses that have been killed, which means they cannot replicate and cause disease, but also do not provide the same type of immune response as live vaccines. The Hepatitis B vaccine utilizes a genetically engineered protein from the virus rather than the live virus itself, making it a subunit vaccine. The tetanus vaccine is formulated from an inactivated toxin (toxoids) produced by the bacterium, rather than using a live pathogen. Each of these other vaccines has its own mechanisms and characteristics but does not fall under the category of live attenuated vaccines like the MMR vaccine does.