Final answer:
The question discusses the incubation periods of vaccinia and variola and the use of non-virulent strains of vaccinia as vehicles for recombinant vaccines. Vaccinia is used for vaccination against smallpox and has a shorter incubation period than the smallpox-causing variola virus. Vaccination with vaccinia is less risky than variolation, which utilizes actual smallpox material.
Step-by-step explanation:
The question pertains to the incubation periods of vaccinia and variola viruses and the use of various virus strains in the production of recombinant sub-unit vaccines. Vaccinia is a virus used as a live vaccine against smallpox. Its close relative, variola, is the virus that causes smallpox. Vaccinia has a shorter incubation period compared to variola. The non-virulent strain of vaccinia is often used as a vehicle to introduce recombinant antigenic epitopes for various diseases, serving as one of the several attenuated vaccine vectors. These vectors, including strains of yellow fever virus, poliovirus, and others, are used to deliver sub-unit vaccines safely.
Variolation was a historical method involving the introduction of smallpox matter into a non-immune individual, which carried a significant risk of causing severe disease. In contrast, vaccination uses a less harmful virus, such as vaccinia, to provoke an immune response without the risk of causing the actual disease. Vaccination is less risky because the vaccinia virus does not cause smallpox and has a lower likelihood of severe side effects.