**Core Concept**
Typhoid revaccination is a critical component of prevention and control strategies in endemic areas, where the risk of infection remains high. The World Health Organization (WHO) and other global health authorities recommend regular booster doses to maintain immunity and prevent outbreaks.

**Why the Correct Answer is Right**
The correct answer, 3 years, is based on the recommendation by the WHO and other global health authorities. This interval is chosen to maintain immunity against *Salmonella Typhi*, the causative agent of typhoid fever. Booster doses are essential to ensure that individuals remain protected against typhoid, particularly in areas with poor sanitation and hygiene. The 3-year interval is also supported by studies demonstrating the waning of immunity over time, making revaccination necessary to maintain adequate protection.

**Why Each Wrong Option is Incorrect**
**Option A:** 1 year is too frequent and may lead to unnecessary exposure to vaccine-related adverse effects. This interval is not recommended by global health authorities.
**Option C:** 5 years may be too long, allowing immunity to wane significantly, increasing the risk of infection and disease.
**Option D:** 10 years is excessively long, and immunity is likely to be significantly compromised, making revaccination essential.

**Clinical Pearl / High-Yield Fact**
In areas with limited resources, typhoid vaccination should be prioritized for individuals at high risk, such as healthcare workers, laboratory personnel, and travelers to endemic areas. The oral typhoid vaccine (Ty21a) is also available and recommended for travelers, particularly those visiting areas with poor sanitation and hygiene.

**✓ Correct Answer: B. 3. 3 years**