## Core Concept
A full course of immunization against Tetanus, typically involving three doses of Tetanus toxoid, is crucial for inducing long-term immunity against Tetanus infection. Tetanus toxoid works by stimulating the body to produce antibodies against the Tetanus toxin, thereby providing immunity. The duration of immunity after a full course of Tetanus toxoid is a key aspect of preventive medicine.

## Why the Correct Answer is Right
The correct answer indicates that a full course of immunization against Tetanus with 3 doses of Tetanus toxoid confers immunity for 10 years. This duration is based on the immunogenicity of Tetanus toxoid and the immune memory it induces. Booster doses are often recommended every 10 years to maintain immunity, especially in regions where Tetanus is common or in individuals at high risk of exposure.

## Why Each Wrong Option is Incorrect
- **Option A:** 1 year - This duration is too short for the immunity provided by a full course of Tetanus toxoid. A primary series of three doses is designed to induce long-term immunity, not just short-term protection.
- **Option B:** 5 years - While some vaccines may require boosters within this timeframe, the primary series for Tetanus toxoid is known to provide longer-lasting immunity.
- **Option D:** 20 years - Although some studies suggest that immunity may persist for longer periods, the generally recommended interval for booster doses to ensure continued protection is 10 years.

## Clinical Pearl / High-Yield Fact
A key point to remember is that after the primary series of Tetanus toxoid, booster doses are recommended every 10 years to maintain immunity. Additionally, in cases of severe or dirty wounds, a booster dose may be indicated even if it's been less than 10 years since the last dose, especially if the individual has not completed the primary series.

**Correct Answer: C. 10 years**