Immunization and Vaccine-Preventable Diseases — MCQs

Question 1: What is the duration of immunity provided by the yellow fever vaccine, and when does it begin?

• A. 6 years starting from 6 days after vaccination
• B. 6 years starting from 10 days after vaccination
• C. 10 years starting from 6 days after vaccination
• D. 10 years starting from 10 days after vaccination (Correct Answer)

Explanation: **Explanation:** The **Yellow Fever vaccine (17D strain)** is a live-attenuated vaccine that provides robust immunity. According to the **International Health Regulations (IHR)**, the validity of the vaccination certificate for international travel traditionally begins **10 days** after the date of vaccination. This 10-day window is the time required for the body to develop protective neutralizing antibodies. **Why Option D is Correct:** Historically, the immunity was documented to last for **10 years**, and the certificate required a booster every decade. While the WHO updated its position in 2016 stating that a single dose provides life-long protection, for the purpose of **NEET-PG and International Health Regulations (IHR)**, the legal validity of the certificate remains defined as starting from **10 days** post-vaccination and lasting for **10 years** (though many countries now accept it as valid for life). **Analysis of Incorrect Options:** * **Options A & B:** The duration of 6 years is incorrect. This figure is often confused with the validity period of the Cholera vaccine certificate (which is 6 months, not years). * **Option C:** While the duration is 10 years, the immunity is not legally recognized until the 10th day. The 6-day period is irrelevant to Yellow Fever protocols. **High-Yield Clinical Pearls for NEET-PG:** * **Strain:** 17D strain (grown in chick embryo). * **Route/Dose:** 0.5 ml, Subcutaneous. * **Contraindications:** Infants <6 months, egg allergy, thymic disease, and symptomatic HIV/immunocompromised states. * **Cold Chain:** It is highly heat-sensitive; must be stored between **+2°C to +8°C** (or frozen at -50°C to -15°C at central levels). * **Rule of 10:** Remember **10 days to 10 years** for easy recall of certificate validity.