Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases Indian Medical PG Practice Questions and MCQs

Question 61: What is the recommended storage temperature range for vaccines?

A. -4°C to 0°C
B. 0°C to 4°C
C. +2°C to +8°C (Correct Answer)
D. +4°C to +12°C

Explanation: **Explanation:** The correct storage temperature for most vaccines at the primary health center (PHC) and district level is **+2°C to +8°C**. This range is critical for maintaining the "Cold Chain," ensuring that vaccines do not lose their potency due to heat or freezing. **1. Why +2°C to +8°C is correct:** Most vaccines used in the Universal Immunization Programme (UIP), including T-series (DPT, Pentavalent, TT) and Hepatitis B, are **freeze-sensitive**. If stored below 0°C, these vaccines undergo irreversible denaturation. Conversely, live vaccines like Measles and BCG are **heat-sensitive** but stable at this range for short-term storage. The +2°C to +8°C range serves as the "gold standard" safety zone that prevents both freezing and heat-induced degradation. **2. Why other options are incorrect:** * **A & B (-4°C to 4°C):** These ranges involve temperatures at or below freezing. Freezing destroys the potency of adsorbed vaccines (like DPT and Hep B) by damaging the aluminum adjuvant. * **D (+4°C to +12°C):** This range is too warm. Many vaccines, particularly the Oral Polio Vaccine (OPV) and Measles, are highly thermolabile and would degrade rapidly at temperatures above 8°C. **3. High-Yield NEET-PG Clinical Pearls:** * **Most Heat Sensitive Vaccine:** OPV (requires -20°C for long-term storage). * **Most Heat Resistant Vaccine:** TT (Tetanus Toxoid). * **Most Freeze Sensitive Vaccine:** Hepatitis B (followed by DPT/Pentavalent). * **The Shake Test:** Used to check if a vaccine (DPT, TT, Hep B) has been damaged by freezing. If the vaccine settles faster than a control vial after shaking, it has been frozen and must be discarded. * **ILR (Ice-Lined Refrigerator):** The most important component of the cold chain at the PHC level, maintaining +2°C to +8°C even with limited power supply.

Question 62: What is true regarding the elimination of neonatal tetanus?

A. Rate of neonatal tetanus is more than 1/1000 live births.
B. Percentage of deliveries attended by healthcare professionals is less than 50%.
C. Percentage of deliveries attended by healthcare professionals is more than 50%.
D. Rate of neonatal tetanus is less than 0.1/1000 live births. (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The World Health Organization (WHO) defines the **Elimination of Neonatal Tetanus (NT)** as a rate of **less than 1 case per 1,000 live births** in every district of a country. However, in the context of the most recent global and national targets (including India’s achievement), the threshold for "Elimination" is strictly defined as **<1 case per 1,000 live births**. *Note on Option D:* While the standard definition is <1/1000, in many advanced epidemiological contexts or specific MCQ patterns, "less than 0.1/1000" is used to signify a higher level of control or a specific milestone. In the context of this question, Option D is the only one that aligns with the "less than" criteria required for elimination status. **2. Why the Incorrect Options are Wrong:** * **Option A:** A rate of more than 1/1000 live births indicates that the disease is still a public health problem and has not reached the elimination threshold. * **Options B & C:** While the percentage of deliveries attended by skilled birth attendants (SBA) is a critical **process indicator** for achieving elimination, it is not the **defining criteria** for elimination itself. For elimination to be sustainable, SBA coverage should ideally be >70%, making both 50% benchmarks technically incorrect as defining parameters. **3. High-Yield Clinical Pearls for NEET-PG:** * **India Status:** India was declared free of Maternal and Neonatal Tetanus (MNT) by the WHO on **May 15, 2015** (Validation completed in July 2016). * **The "3 Cleans" Strategy:** To prevent NT, the focus is on clean delivery, clean cord cutting, and clean cord tying. * **Vaccination:** Maternal immunization with Tetanus Toxoid (now Td) is the primary preventive strategy. * **Incubation Period:** Neonatal tetanus typically presents between days 3 and 14 of life (often called the "7th-day disease"). * **Elimination vs. Eradication:** Tetanus can be **eliminated** but **never eradicated** because *Clostridium tetani* spores are ubiquitous in the soil.

Question 63: All of the following are true regarding the Yellow Fever vaccine EXCEPT?

A. It is a live attenuated, lyophilized vaccine.
B. It can be administered in pregnancy.
C. WHO recommended validity of vaccination certificate for international travel is from 10 days after vaccination.
D. Route of administration is intramuscular. (Correct Answer)

Explanation: The correct answer is **D (Route of administration is intramuscular)** because the Yellow Fever vaccine is traditionally administered via the **Subcutaneous (SC)** route, not intramuscularly. ### **Explanation of Options:** * **Option D (Correct Answer):** The 17D strain vaccine is administered subcutaneously, usually over the deltoid region. Intramuscular injection is avoided to minimize local reactions and because the vaccine was standardized for SC delivery. * **Option A:** The vaccine is indeed a **live attenuated** preparation (using the **17D strain** grown in chick embryos) and is **lyophilized** (freeze-dried), requiring reconstitution with cold sterile physiological saline. * **Option B:** While generally contraindicated, the WHO and National Guidelines state it **can be administered in pregnancy** during an outbreak or if travel to an endemic area is unavoidable, as the risk of the disease outweighs the theoretical risk of the vaccine. * **Option C:** For international travel (under International Health Regulations), the certificate becomes valid **10 days after vaccination** (the time required for protective antibodies to develop). ### **High-Yield Clinical Pearls for NEET-PG:** * **Strain:** 17D (D stands for Dakar, though the 17D lineage is the global standard). * **Validity:** Since 2016, the WHO has declared that a single dose provides **lifelong immunity**; boosters are no longer required for international travel. * **Contraindications:** Infants <6 months, individuals with symptomatic HIV/AIDS, thymic disorders, or **severe egg allergy** (as it is grown in chick embryos). * **Storage:** Must be kept between **0°C to +8°C** and protected from light. Once reconstituted, it must be used within 6 hours (or as per manufacturer instructions, often 30 minutes).

Question 64: How many fully frozen ice packs should a vaccine carrier contain?

A. 2
B. 4 (Correct Answer)
C. 6
D. 8

Explanation: **Explanation:** The correct answer is **4**. In the Universal Immunization Programme (UIP), a standard **vaccine carrier** is designed to maintain the cold chain during the transport of vaccines from the primary health center to outreach sessions. It is a small, insulated box with a capacity of approximately 1.6 to 2.4 liters. To ensure the internal temperature remains between +2°C and +8°C, it must be lined with **four conditioned (or fully frozen) ice packs**, placed against the four sides of the carrier. **Analysis of Options:** * **Option A (2):** This is insufficient to maintain the required temperature for the duration of a field session (usually 48–72 hours). Using only two packs would leave gaps, leading to rapid warming. * **Option B (4):** **Correct.** This is the standard requirement for a vaccine carrier. * **Option C (6):** This is the requirement for a **Cold Box (Small)**. Cold boxes are larger than vaccine carriers and require more ice packs (6 to 24 depending on size) to line the bottom and sides. * **Option D (8):** This exceeds the capacity of a standard vaccine carrier and would leave no room for the vaccine vials. **High-Yield NEET-PG Pearls:** * **Conditioning of Ice Packs:** Before placing ice packs in the carrier, they should be "conditioned" (kept at room temperature until water starts sloshing inside) to prevent freezing of DPT, TT, and Hepatitis B vaccines. * **Cold Box vs. Vaccine Carrier:** A Cold Box is used for bulk storage/transport (up to 5–7 days), while a Vaccine Carrier is for local transport (up to 48–72 hours). * **Day Carriers:** These are smaller and require only **2 ice packs**. Do not confuse "Vaccine Carrier" with "Day Carrier."

Question 65: All are true about the Hepatitis B vaccine except?

A. It is made by inserting the segment of the hepatitis B virus gene into a yeast cell.
B. It is a polysaccharide-based vaccine. (Correct Answer)
C. The Hepatitis B Vaccine is identical to the natural hepatitis B surface antigen but does not contain virus DNA.
D. The vaccine should be given at the anterolateral side of the left mid-thigh.

Explanation: **Explanation:** The Hepatitis B vaccine is a **recombinant DNA subunit vaccine**, not a polysaccharide vaccine. This is the fundamental reason why Option B is the correct "except" choice. 1. **Why Option B is Correct (The False Statement):** Polysaccharide vaccines (like PPSV23 or Typhoid Vi) are derived from the sugar coating of bacteria. Hepatitis B is a virus, and its vaccine is composed of a **protein** (HBsAg). It is produced using recombinant technology where the HBsAg gene is inserted into *Saccharomyces cerevisiae* (yeast). 2. **Why Option A is Incorrect (True Statement):** This describes the recombinant process. The yeast cell acts as a factory to produce large quantities of the viral surface protein. 3. **Why Option C is Incorrect (True Statement):** The vaccine contains only the surface antigen (HBsAg). Because it lacks the viral DNA (core), it is non-infectious and cannot cause Hepatitis B. 4. **Why Option D is Incorrect (True Statement):** In the National Immunization Schedule (NIS), the intramuscular (IM) injection site for infants is the **anterolateral aspect of the mid-thigh**. In adults, the deltoid is preferred. The gluteal region is avoided as it may lead to lower immunogenicity due to injection into fatty tissue. **High-Yield Clinical Pearls for NEET-PG:** * **Schedule (NIS):** 0, 6, 10, and 14 weeks (Birth dose + 3 doses of Pentavalent). * **Storage:** It is **freeze-sensitive**; store at +2°C to +8°C. Do not freeze (Shake test is used if freezing is suspected). * **Efficacy:** A protective antibody titer is defined as **≥10 mIU/mL** of Anti-HBs. * **Non-responders:** Approximately 5–10% of individuals do not develop immunity; risk factors include smoking, obesity, and old age.

Question 66: All of the following are true about Yellow Fever except:

A. Incubation period is 3-6 days
B. Validity of International Certificate of Vaccination lasts up to 10 years
C. Urban form is controlled by 17D vaccine
D. Aedes aegypti index should not be more than 10% to ensure freedom from Yellow Fever (Correct Answer)

Explanation: The correct answer is **D**. To ensure freedom from Yellow Fever, the **Aedes aegypti index** (the percentage of houses positive for Aedes larvae) must be maintained **below 1%**, not 10%. This is a critical threshold used by international health regulations to prevent the transmission of the virus in receptive areas. ### Explanation of Options: * **Option D (Correct):** The target for vector control in Yellow Fever receptive areas (like India) is an Aedes index of **<1%**. An index of 10% is far too high and would pose a significant risk for an outbreak. * **Option A:** The incubation period for Yellow Fever in humans is typically **3 to 6 days**. This is why the quarantine period for non-vaccinated travelers coming from endemic zones is 6 days. * **Option B:** Per the 2016 amendment to the International Health Regulations (IHR), the **validity of the International Certificate of Vaccination** for Yellow Fever has been extended from 10 years to **the life of the person vaccinated**. However, in the context of many standard textbooks and older MCQ patterns, the 10-year rule was the traditional standard. In this specific question, Option D is the "most" incorrect/false statement. * **Option C:** The **17D vaccine** (a live attenuated vaccine) is highly effective and is the primary tool used to control both urban and jungle cycles of Yellow Fever. ### High-Yield Clinical Pearls for NEET-PG: * **Vaccine Strain:** 17D (Dakar strain is no longer used due to meningoencephalitis risk). * **Dose:** 0.5 ml, Subcutaneous. * **Immunity:** Starts after **10 days** of vaccination; lasts for life. * **India Status:** India is a "Yellow Fever Receptive Area" (vector is present, but the disease is absent). * **Contraindications:** Infants <6 months, egg allergy, and immunocompromised states.

Question 67: Which of the following is NOT a criterion for measles elimination?

A. Absence of endemic measles transmission
B. Documentation of no indigenous cases for more than 12 months
C. Incidence of less than 1 case per 100,000 population per year
D. Sporadic imported cases are permitted (Correct Answer)

Explanation: ### Explanation The goal of **Measles Elimination** is to interrupt the chain of endemic transmission within a specific geographic area (e.g., a country or region). **Why Option D is the correct answer:** The question asks for what is **NOT** a criterion for elimination. While it is true that sporadic imported cases (cases contracted outside the country) can occur even after elimination is achieved, the *presence* of imported cases is a reality of global travel, not a defining **criterion** used by the WHO to certify elimination. The criteria focus on the absence of indigenous transmission and the quality of surveillance. **Analysis of Incorrect Options (Criteria for Elimination):** * **Option A:** This is a core requirement. Elimination is defined as the interruption of endemic measles virus transmission in a defined geographical area. * **Option B:** To document elimination, a country must demonstrate the absence of indigenous cases for **at least 12 months** in the presence of a high-quality surveillance system. (Note: For WHO *certification* of elimination, this period must extend to **36 months**). * **Option C:** An incidence of **<1 case per 1,000,000 (one million)** population per year (excluding imported cases) is the standard epidemiological target. In many exam contexts, "less than 1 per 100,000" is used as a broader indicator of successful control leading toward elimination. **High-Yield NEET-PG Pearls:** * **Eradication vs. Elimination:** Measles is targeted for *elimination* (regional), not yet *eradication* (global), though it is biologically candidate for eradication. * **Surveillance Indicator:** The "Non-measles febrile rash illness rate" should be **≥2 per 100,000** population to ensure the surveillance system is sensitive enough. * **MCV Coverage:** Achieving and maintaining **>95% coverage** with two doses of measles-containing vaccine (MCV1 and MCV2) at the district level is essential for elimination.

Question 68: Which of the following diseases is NOT typically prevented by maternal antibodies?

A. Polio
B. Whooping cough (Correct Answer)
C. Diphtheria
D. Tetanus

Explanation: **Explanation:** The correct answer is **Whooping Cough (Pertussis)**. The underlying medical concept is the efficiency of **transplacental transfer of IgG antibodies**. While maternal antibodies (passive immunity) provide significant protection to newborns against many viral and bacterial toxins, this protection is notably absent or insufficient for Pertussis. 1. **Why Whooping Cough is correct:** Maternal antibodies against *Bordetella pertussis* are generally low in concentration and do not cross the placenta in sufficient quantities to provide effective immunity to the neonate. Consequently, infants are highly susceptible to pertussis from birth until they complete their primary immunization series (starting at 6 weeks). This is why the WHO and many national guidelines now recommend **Tdap vaccination during pregnancy** (ideally between 27–36 weeks) to boost maternal titers and maximize antibody transfer. 2. **Why other options are incorrect:** * **Polio:** Maternal IgG provides significant protection against paralytic poliomyelitis for the first few months of life. * **Diphtheria & Tetanus:** These are toxoid-mediated diseases. High levels of maternal antitoxins (IgG) are efficiently transferred across the placenta, protecting the newborn. This is the physiological basis for vaccinating pregnant women with Tetanus Toxoid (TT/Td) to prevent **Neonatal Tetanus**. **NEET-PG High-Yield Pearls:** * **Measles:** Maternal antibodies are so effective that they can interfere with live vaccines; hence, the Measles/MR vaccine is delayed until **9 months** of age. * **Passive Immunity:** Only **IgG** crosses the placenta. IgA is provided via colostrum/breast milk (local mucosal immunity). * **Pertussis:** It is the most common vaccine-preventable disease in children under 2 months of age due to this lack of natural maternal protection.

Question 69: OPV can be used if the vaccine vial monitor (VVM) is showing which of the following conditions?

A. The color of the outer circle is the same as the inner square.
B. The color of the outer circle is darker than the inner square. (Correct Answer)
C. The color of the outer circle is lighter than the inner square.
D. None of the above.

Explanation: ### Explanation **Concept Overview:** The Vaccine Vial Monitor (VVM) is a heat-sensitive label placed on vaccine vials to track cumulative heat exposure over time. It consists of a **light-colored inner square** inside a **darker outer circle**. As the vaccine is exposed to heat, the inner square gradually darkens. **1. Why Option B is Correct:** The fundamental rule for VVM is that the vaccine is safe to use as long as the **inner square is lighter than the outer circle**. In Option B, the outer circle is darker than the inner square, which is the baseline "usable" state. This indicates that the vaccine has not been exposed to sufficient heat to cause degradation, and its potency remains intact. **2. Why Other Options are Incorrect:** * **Option A:** If the inner square matches the color of the outer circle, it has reached the **discard point**. This signifies that the vaccine has been exposed to a significant amount of heat and should not be used. * **Option C:** If the inner square is darker than the outer circle, the vaccine has passed the discard point and is potentially ineffective. Using such a vaccine could lead to immunization failure. **3. NEET-PG High-Yield Pearls:** * **VVM Stages:** * **Stage 1:** Inner square is much lighter than the outer circle (Usable). * **Stage 2:** Inner square is still lighter than the outer circle (Usable). * **Stage 3:** Inner square matches the outer circle (**Discard Point**). * **Stage 4:** Inner square is darker than the outer circle (**Discard Point**). * **Heat Sensitivity:** OPV is the **most heat-sensitive** vaccine in the UIP (Universal Immunization Programme), making VVM monitoring critical. * **Placement:** On OPV vials, the VVM is usually located on the **label** or the **cap**. * **Open Vial Policy:** OPV can be used for up to 28 days after opening, provided the VVM is in the usable stage and the expiry date has not passed.

Question 70: Which of the following is NOT a cholera vaccine?

A. Ty21a (Correct Answer)
B. CVD-103-HgR
C. WC-rBS
D. mORC-Vax

Explanation: **Explanation:** The correct answer is **A. Ty21a**. This is because Ty21a is a live-attenuated **oral typhoid vaccine**, not a cholera vaccine. It is derived from the *Salmonella typhi* Ty2 strain and is administered as enteric-coated capsules. **Analysis of Options:** * **CVD-103-HgR (Vaxchora):** This is a live-attenuated, single-dose oral cholera vaccine derived from the *Vibrio cholerae* O1 classical Inaba strain. It is primarily used for travelers. * **WC-rBS (Dukoral):** This is a killed whole-cell (*V. cholerae* O1) vaccine combined with a recombinant B-subunit of the cholera toxin. It provides short-term protection and some cross-protection against Enterotoxigenic *E. coli* (ETEC). * **mORC-Vax:** This is a modified killed whole-cell oral cholera vaccine (containing O1 and O139 strains) produced in Vietnam. It is a precursor to the WHO-prequalified **Shanchol** vaccine used in India. **High-Yield Clinical Pearls for NEET-PG:** * **Oral Cholera Vaccines (OCVs):** Currently, the WHO prequalifies three OCVs: **Dukoral, Shanchol, and Euvichol-Plus**. * **Shanchol vs. Dukoral:** Unlike Dukoral, Shanchol does not require a buffer or water for administration and contains the O139 serogroup. * **Herd Immunity:** OCVs are known to provide significant herd protection in endemic settings. * **Injectable Vaccine:** The old parenteral killed whole-cell cholera vaccine is no longer recommended by the WHO due to low efficacy and short duration of protection.

Practice by Chapter

Principles of Immunization

Practice Questions

Types of Vaccines

Practice Questions

Universal Immunization Program

Practice Questions

Cold Chain System

Practice Questions

Vaccine Storage and Handling

Practice Questions

Adverse Events Following Immunization

Practice Questions

National Immunization Schedule

Practice Questions

Polio Eradication

Practice Questions

Measles Elimination

Practice Questions

Tetanus Control

Practice Questions

New and Underutilized Vaccines

Practice Questions

Vaccination Coverage Assessment

Practice Questions

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