**Question:** Nakayama strain is used in vaccination of

A. Bacille Calmette-Guérin (BCG) vaccine for tuberculosis
B. Polio vaccine
C. Hepatitis B vaccine
D. Measles vaccine

**Core Concept:** Nakayama strain refers to a specific strain of bacilli, which is a variant of the Mycobacterium bovis bacteria. This strain is used in the production of the Bacille Calmette-Guérin (BCG) vaccine, which is a live attenuated vaccine against tuberculosis (TB).

**Why the Correct Answer is Right:** Nakayama strain was isolated from a patient with tuberculosis and was found to be highly attenuated, meaning it is less virulent but retains the ability to stimulate an immune response. This strain is used in the BCG vaccine due to its ability to induce strong cell-mediated immunity against Mycobacterium tuberculosis, the causative agent of TB. BCG vaccine is effective against severe forms of childhood TB and has some protection against adult pulmonary TB.

**Why Each Wrong Option is Incorrect:**

A. Bacille Calmette-Guérin (BCG) vaccine is made from the Nakayama strain of Mycobacterium bovis, not Bacille Calmette-Guérin.

B. Polio vaccine is made from attenuated strains of the poliovirus, not from the Nakayama strain of Mycobacterium bovis.

C. Hepatitis B vaccine is made from a recombinant DNA technology, using the hepatitis B surface antigen (HBsAg) from the hepatitis B virus, not from the Nakayama strain of Mycobacterium bovis.

D. Measles vaccine is made from attenuated strains of the measles virus, not from the Nakayama strain of Mycobacterium bovis.

**Clinical Pearl:** The Nakayama strain is an important example of how the process of attenuation (reducing the virulence of a pathogen) is used in the development of live attenuated vaccines. In the case of the BCG vaccine, the Nakayama strain is highly attenuated, making it both safe for human use and capable of inducing a strong immune response.