**Question:** Salk polio vaccine is -

A. Inactivated poliovirus vaccine
B. Live attenuated poliovirus vaccine
C. Subunit vaccine
D. Monovalent vaccine

**Core Concept:** The Salk polio vaccine refers to one of the two primary types of polio vaccines developed by Jonas Salk. The two main types are inactivated (Salk) and live attenuated (Sabin) vaccines.

**Why the Correct Answer is Right:** The Salk polio vaccine is an inactivated poliovirus vaccine, which means it is made from killed or inactivated poliovirus particles that are unable to cause disease but can stimulate the immune system to produce an immune response against the virus. The vaccine is typically administered through a single injection, and its primary mechanism involves the activation of B-cells to produce antibodies against poliovirus.

**Why Each Wrong Option is Incorrect:**

A. Inactivated poliovirus vaccine (Salk)
B. Live attenuated poliovirus vaccine (Sabin)
C. Subunit vaccine: This term refers to a type of vaccine that contains a specific protein or subunit of a pathogen, not relevant to the Salk polio vaccine.
D. Monovalent vaccine: A monovalent vaccine contains a single antigenic strain of a pathogen, while the Salk polio vaccine contains three inactivated strains of the virus to provide broader protection against all three serotypes of poliovirus.

**Clinical Pearl:** Jonas Salk's polio vaccine, specifically the inactivated poliovirus vaccine, played a significant role in eradicating polio globally. As of 2021, the world has seen a significant decline in polio cases, with vaccination campaigns being instrumental in this progress. The Salk vaccine, along with the Sabin vaccine, contributed to the decline in polio cases globally.

**Correct Answer:** A. Inactivated poliovirus vaccine (Salk)

The Salk polio vaccine is an inactivated poliovirus vaccine, which means it is prepared from killed or inactivated poliovirus particles that are unable to cause disease but can stimulate the immune system to produce an immune response against the virus. This vaccine is typically administered through a single injection, and its primary mechanism involves B-cells to produce antibodies against poliovirus.