Immunization and Vaccine-Preventable Diseases Practice Questions

Q: What diphtheria antibody titer is considered optimally protective?

>0.1 IU/ml. **Explanation:** The protective efficacy of the diphtheria vaccine is directly correlated with the serum antitoxin concentration. In Community Medicine and Pediatrics, these titers are categorized into levels of protection: 1. **Correct Answer (A): >0.1 IU/ml** is considered the **optimal or full protective level**. At this concentration, an individual is highly unlikely to develop clinical diphtheria even upon exposure to toxigenic *Corynebacterium diphtheriae*. This is the standard target for long-term immunity following a complete primary series and boosters. 2. **Incorrect Options:** * **B (>0.01 IU/ml):** This is the **minimum protective level** (basic protection). While it may prevent death, it does not reliably prevent clinical disease in all individuals. * **C (>0.05 IU/ml):** This is an intermediate level often cited as "partial protection" but is not the standard threshold for "optimal" immunity. * **D (0.5 IU/ml):** This value is significantly higher than the required threshold for protection and is not used as a standard clinical benchmark for diphtheria immunity. **High-Yield Clinical Pearls for NEET-PG:** * **Schick Test:** Historically used to determine susceptibility to diphtheria. A positive test (inflammation) indicates a titer **<0.01 IU/ml** (susceptible), while a negative test indicates immunity. * **Vaccine Type:** Diphtheria toxoid is an **adsorbed vaccine** (using aluminum salts) to enhance immunogenicity. * **Storage:** It is highly heat-stable but **freeze-sensitive**. It must be stored at +2°C to +8°C; if frozen, the "Shake Test" is used to check for damage. * **Herd Immunity:** To prevent epidemics, a community coverage of approximately 70-75% is required.

Q: A neonate developed a side effect following BCG vaccination. Which of the following side effects is the neonate most likely to develop after vaccination?

Ulceration. **Explanation:** The BCG (Bacillus Calmette-Guérin) vaccine is a live attenuated vaccine derived from *Mycobacterium bovis*. Following intradermal administration, a predictable sequence of local reactions occurs, which are considered normal responses rather than adverse events. **Why Ulceration is the Correct Answer:** After vaccination, a papule forms at 2–3 weeks, which increases in size and eventually undergoes **ulceration** by 4–8 weeks. This ulcer is the most common "side effect" or expected reaction. It typically heals spontaneously within 6–12 weeks, leaving behind the characteristic permanent circular scar. **Analysis of Incorrect Options:** * **A. Fever:** Systemic reactions like fever are extremely rare following BCG vaccination. It is primarily a localized reaction. * **C. Osteomyelitis:** This is a very rare, late complication (1 in 1,000,000 doses) occurring due to hematogenous spread, usually seen in immunocompromised infants. * **D. Regional lymphadenitis:** While common (suppurative or non-suppurative), it occurs less frequently than the standard ulceration. It is considered a complication if the lymph nodes exceed 1.5 cm or become fluctuant. **High-Yield Clinical Pearls for NEET-PG:** * **Strain used in India:** Danis 1331 strain. * **Dose:** 0.05 ml for neonates (below 1 month) and 0.1 ml for infants above 1 month. * **Site/Route:** Left upper arm (deltoid region), strictly **intradermal** (using a tuberculin/Omega syringe). * **Protective Effect:** Highly effective against TB meningitis and miliary TB in children, but has variable efficacy against adult pulmonary TB. * **Contraindication:** BCG is contraindicated in symptomatic HIV-infected infants or those with known immunodeficiency.

Question 1

A 35-year-old healthcare worker from India is posted to a sub-Saharan African country for WHO work. She has never had yellow fever. What is the most appropriate vaccination strategy?

Accepted Answer

Single dose of yellow fever vaccine at least 10 days before travel

Answer

Two doses of yellow fever vaccine 4 weeks apart

Answer

Yellow fever immunoglobulin followed by vaccine

Answer

Yellow fever vaccine with booster after 10 years

Question 2

What diphtheria antibody titer is considered optimally protective?

Accepted Answer

>0.1 IU/ml

Answer

>0.01 IU/ml

Answer

>0.05 IU/ml

Answer

0.5 IU/ml

Question 3

A neonate developed a side effect following BCG vaccination. Which of the following side effects is the neonate most likely to develop after vaccination?

Accepted Answer

Ulceration

Answer

Fever

Answer

Osteomyelitis

Answer

Regional lymphadenitis

Question 4

For how many days must residual weakness be observed in a case of acute flaccid paralysis to confirm poliomyelitis?

Accepted Answer

60 days

Answer

30 days

Answer

42 days

Answer

90 days

Question 5

What is the recommended Tetanus Toxoid (TT) vaccination schedule for a primigravida woman during pregnancy?

Accepted Answer

Two doses, one month apart, administered as soon as possible during pregnancy.

Answer

One dose in the second trimester.

Answer

Two doses, one month apart, in the second trimester.

Answer

One dose administered anytime as soon as possible during pregnancy.

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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