**Question:** Strain used in Mumps vaccine

**Core Concept:** Mumps is a viral infection caused by the mumps virus, which belongs to the Paramyxoviridae family. The mumps vaccine is a live-attenuated vaccine that helps prevent mumps infection.

**Why the Correct Answer is Right:**
The correct answer is **D.** The Jeryl Lynn strain is the strain used in mumps vaccine preparations, such as the Mumps component of the MMR vaccine (Mumps, Measles, and Rubella). The Jeryl Lynn strain was first isolated in 1954 from a patient with mumps and then further attenuated to develop the vaccine strain. This strain has been shown to be highly immunogenic, inducing a robust immune response against mumps infection.

**Why Each Wrong Option is Incorrect:**
A. The Morbilli strain is another strain of the mumps virus, but it is not used in the mumps vaccine. The Morbilli strain is not attenuated enough for use in a vaccine, leading to a lower immunogenicity compared to the Jeryl Lynn strain.
B. The Urabe strain is another mumps vaccine strain, but it has been associated with severe neurological complications, specifically meningitis and encephalitis. As a result, the Urabe strain is no longer used in the mumps vaccine.
C. The wild-type mumps virus is the natural form of the mumps virus found in nature. However, using the wild-type virus in a vaccine would be risky due to the potential for causing severe side effects and complications.

**Clinical Pearl:**
The Jeryl Lynn strain is a highly attenuated form of the mumps virus that has been extensively studied and proven to be safe and effective in inducing a robust immune response against mumps infection. The Mumps component of the MMR vaccine, which stands for Measles, Mumps, and Rubella, uses the Jeryl Lynn strain to protect against mumps infection. This ensures a higher level of immunogenicity compared to other strains and minimizes the risk of severe side effects.