**Core Concept**
Tetanus immunization is a form of active immunization that provides long-term protection against the toxin produced by Clostridium tetani. The immunity conferred by Tetanus toxoid vaccination is not lifelong, and booster shots are necessary to maintain adequate levels of antibodies.

**Why the Correct Answer is Right**
The duration of immunity after a full course of Tetanus toxoid vaccination is typically around 10 years. This is because the booster shots stimulate the production of memory B cells, which can quickly differentiate into antibody-secreting plasma cells upon re-exposure to the antigen. The immunity is not lifelong due to the gradual waning of antibody levels over time. A booster shot is necessary to maintain adequate levels of antibodies to protect against Tetanus.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a full course of Tetanus toxoid vaccination does not provide lifelong immunity.
**Option B:** This option is incorrect because the duration of immunity after a full course of Tetanus toxoid vaccination is not typically around 5 years.
**Option C:** This option is incorrect because the duration of immunity after a full course of Tetanus toxoid vaccination is not typically around 20 years.

**Clinical Pearl / High-Yield Fact**
It's essential to note that a booster shot is necessary to maintain adequate levels of antibodies to protect against Tetanus, especially in individuals who have not received a booster shot in the past 10 years.

**Correct Answer:** C. 10 years.