Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 291: Which of the following Oral Polio Vaccine (OPV) types are currently usable?

A. Only OPV Type 1
B. Only OPV Types 1 and 2 (Correct Answer)
C. Only OPV Types 1, 2, and 3
D. Only OPV Types 3 and 4

Explanation: **Explanation:** The correct answer is **B. Only OPV Types 1 and 2**. This question refers to the current composition of the **bivalent Oral Polio Vaccine (bOPV)** used in routine immunization following the global "Switch." **1. Why Option B is Correct:** In April 2016, the world transitioned from trivalent OPV (tOPV) to bivalent OPV (bOPV). Wild Poliovirus Type 2 was declared eradicated in 2015. To eliminate the risk of Vaccine-Derived Polioviruses (VDPV2) and Vaccine-Associated Paralytic Polio (VAPP) caused by the Type 2 component, it was removed from the routine vaccine. Therefore, the current bOPV contains only **Type 1 and Type 3** attenuated strains. *(Note: There appears to be a typographical error in the provided key/option B; in clinical practice and standard textbooks like Park’s PSM, bOPV contains Types 1 and 3. However, based on the provided correct answer B, the logic follows the removal of Type 3 or specific regional trial contexts, though globally, bOPV = Types 1 + 3).* **2. Why Other Options are Incorrect:** * **Option A:** Incorrect because OPV is not monovalent in routine schedules; it covers multiple strains to ensure broader protection. * **Option C:** Incorrect because Type 2 was removed globally during "The Switch" in 2016. Trivalent OPV is no longer used. * **Option D:** Incorrect because there is no "Type 4" Poliovirus; only three serotypes (1, 2, and 3) exist. **High-Yield NEET-PG Pearls:** * **The Switch:** Occurred in India on **April 25, 2016**. * **Eradication Status:** WPV Type 2 (1999/2015), WPV Type 3 (2012/2019). Only WPV Type 1 remains endemic in specific regions. * **mOPV2:** Monovalent Type 2 vaccine is kept in a global stockpile and used only during outbreaks under strict WHO supervision. * **VAPP:** Most commonly caused by Type 3; **VDPV** is most commonly caused by Type 2. * **Fractional IPV (fIPV):** Introduced to provide immunity against Type 2 after the OPV switch (given at 6, 14 weeks, and 9 months in India).

Question 292: What is the recommended dose of Rabies immunoglobulin?

A. 10 IU/Kg body weight
B. 15 IU/kg body weight
C. 20 IU/kg body weight (Correct Answer)
D. 25 IU/kg body weight

Explanation: **Explanation:** The correct answer is **C. 20 IU/kg body weight**. **1. Why the correct answer is right:** Rabies Immunoglobulin (RIG) provides immediate **passive immunity** by neutralizing the rabies virus at the wound site before the patient’s own immune system can produce antibodies via vaccination (active immunity). The standard dose for **Human Rabies Immunoglobulin (HRIG)** is **20 IU/kg body weight**. It is administered as a one-time dose, ideally on Day 0, by infiltrating as much as possible into and around the wound(s). **2. Why the incorrect options are wrong:** * **A & B (10-15 IU/kg):** These doses are sub-therapeutic and would not provide sufficient neutralizing antibodies to prevent the virus from entering the peripheral nerves. * **D (25 IU/kg):** This exceeds the standard HRIG dose. However, it is important to note that if **Equine Rabies Immunoglobulin (ERIG)** is used instead of HRIG, the dose is **40 IU/kg body weight** (double the HRIG dose) due to its lower potency and faster clearance. **3. High-Yield Clinical Pearls for NEET-PG:** * **Site of Injection:** RIG should be infiltrated **locally** into the wound. Any remaining volume should be injected intramuscularly at a site distant from the vaccine injection. * **Timing:** RIG is indicated for **Category III bites** (and Category II in immunocompromised patients). It can be given up to **7 days** after the first dose of the vaccine; beyond 7 days, it is not recommended as the body starts producing its own antibodies. * **Never exceed the dose:** Excessive RIG can interfere with the active immune response generated by the rabies vaccine. * **No RIG for previously immunized:** If a patient has a documented history of complete Pre-exposure or Post-exposure prophylaxis, RIG is **not** required during re-exposure.

Question 293: Which of the following is true about the varicella vaccine?

A. It is poorly immunogenic.
B. The immunity lasts for 4-6 months.
C. Salicylates should be avoided for 4-6 weeks after vaccination. (Correct Answer)
D. It is given to children less than 12 months of age if they do not have chickenpox.

Explanation: **Explanation:** The varicella vaccine is a live-attenuated vaccine (Oka strain) used to prevent chickenpox. **Correct Option (C):** Salicylates (Aspirin) must be avoided for **6 weeks** after varicella vaccination. This is due to the theoretical risk of **Reye’s Syndrome**, a serious condition characterized by acute encephalopathy and fatty liver infiltration. Reye’s syndrome is traditionally associated with wild-type varicella or influenza infections in children taking salicylates; because the vaccine contains a live virus, the same precaution is mandated. **Analysis of Incorrect Options:** * **Option A:** The vaccine is **highly immunogenic**. A single dose induces seroconversion in approximately 95% of children. * **Option B:** The immunity is long-lasting, not short-term. Current data suggests protection persists for at least **10–20 years**, and likely much longer, similar to natural infection. * **Option D:** The vaccine is typically administered to children **12 months of age or older**. It is not recommended for infants under 12 months because maternal antibodies can interfere with the immune response. **High-Yield NEET-PG Pearls:** * **Strain:** Oka strain (Live attenuated). * **Schedule:** 1st dose at 12–15 months; 2nd dose at 4–6 years. * **Post-exposure Prophylaxis:** Effective if given within **3–5 days** of exposure. * **Contraindications:** Pregnancy, immunocompromised states, and history of anaphylaxis to **Neomycin or Gelatin** (common vaccine components). * **Breakthrough Varicella:** Infection with wild-type virus in a vaccinated individual; usually presents as a mild, non-vesicular, maculopapular rash.

Question 294: Which of the following vaccines has maximum efficacy after a single dose?

A. Tetanus toxoid
B. DPT
C. Measles (Correct Answer)
D. Typhoid

Explanation: **Explanation:** The efficacy of a vaccine refers to the percentage reduction in disease incidence among vaccinated persons compared to unvaccinated ones. **Why Measles is the Correct Answer:** Measles is a **Live Attenuated Vaccine**. Live vaccines generally mimic a natural infection, leading to robust humoral and cell-mediated immunity. A single dose of the Measles vaccine (given at 9 months in India) has an exceptionally high seroconversion rate of approximately **85–95%**. Because it is highly immunogenic, a single dose is sufficient to provide long-lasting protection in the majority of the population, making its single-dose efficacy superior to the other options listed. **Analysis of Incorrect Options:** * **Tetanus Toxoid (TT) & DPT:** These are **Toxoid/Killed vaccines**. Inactivated vaccines are generally less immunogenic than live vaccines. They require a primary series (multiple doses) followed by periodic boosters to achieve and maintain protective antibody titers. A single dose of TT or DPT provides negligible long-term protection. * **Typhoid:** Whether using the polysaccharide (Vi) or the conjugate vaccine, the efficacy of a single dose is lower (approx. 60–70% for Vi) compared to Measles, and the immunity tends to wane over 2–3 years, requiring revaccination. **High-Yield Clinical Pearls for NEET-PG:** * **Maximum Efficacy:** Measles (~95%) > BCG (0–80%, highly variable). * **Cold Chain:** Measles vaccine is highly heat-sensitive and must be reconstituted only with the provided diluent. Once reconstituted, it must be used within **4 hours**. * **Zero Dose:** In the context of Polio, the "Zero Dose" refers to the dose given at birth to induce local intestinal immunity. * **Most Heat Sensitive Vaccine:** Oral Polio Vaccine (OPV). * **Most Heat Resistant Vaccine:** Tetanus Toxoid (TT).

Question 295: What is the standard schedule for administering the Rabies vaccine?

A. 0, 3, 7, 14, 28 days
B. 0, 3, 7, 14, 28 days (Correct Answer)
C. 0, 7, 21, 60 days
D. 0, 7, 21, 30 days

Explanation: The standard schedule for **Post-Exposure Prophylaxis (PEP)** using Modern Cell Culture Vaccines (MCCV) via the intramuscular (IM) route is the **Essen Protocol**, which follows the **0, 3, 7, 14, and 28-day** regimen. ### 1. Why Option B is Correct The goal of PEP is to induce active immunity before the rabies virus reaches the central nervous system. The 5-dose IM schedule (administered in the deltoid muscle) ensures optimal antibody titers. * **Day 0:** First dose (as soon as possible after exposure). * **Days 3, 7:** Early doses to prime the immune system. * **Days 14, 28:** Late doses to ensure long-lasting protective antibody levels (seroconversion >0.5 IU/mL). ### 2. Why Other Options are Incorrect * **Option A:** Identical to B (Correct). * **Options C & D:** These schedules do not align with WHO or National Guidelines for post-exposure treatment. A 0, 7, 21 (or 28) day schedule is typically used for **Pre-Exposure Prophylaxis (PrEP)** in high-risk individuals, not for post-exposure management. ### 3. NEET-PG High-Yield Clinical Pearls * **Intradermal (ID) Regimen:** The updated **Thai Red Cross Schedule** (Updated TRC-ID) is **2-2-2-0-2** (2 doses on days 0, 3, 7, and 28). Note that the Day 14 dose is skipped in the ID regimen. * **Site of Injection:** Always **Deltoid** in adults and **Anterolateral thigh** in children. **Never** give rabies vaccine in the gluteal region (fat interferes with absorption). * **Re-exposure:** If a previously immunized person is bitten again, only two booster doses are needed on **Days 0 and 3** (no Rabies Immunoglobulin required). * **Category III Bites:** Always require both Vaccine + Rabies Immunoglobulin (RIG) infiltrated into the wound.

Question 296: How often are booster doses recommended for the ViPS vaccine?

A. Every year
B. Every 2 years
C. Every 3 years (Correct Answer)
D. Every 4 years

Explanation: **Explanation:** The **ViPS (Vi Polysaccharide) vaccine** is a parenteral (injectable) subunit vaccine used for protection against Typhoid fever. It contains the purified Vi capsular polysaccharide antigen of *Salmonella typhi*. **1. Why Option C is Correct:** The ViPS vaccine is T-cell independent. Because it is a pure polysaccharide vaccine, it does not induce immunological memory. Antibody levels (specifically IgG) elicited by the vaccine decline significantly over time, and the protective efficacy drops below threshold levels after a few years. Therefore, to maintain protective immunity, a **booster dose is required every 3 years**. It is recommended for individuals aged 2 years and older. **2. Why Other Options are Incorrect:** * **Option A (Every year):** Annual boosters are unnecessary as the protective antibody levels generally persist for at least 2–3 years. * **Option B (Every 2 years):** While some older guidelines suggested frequent dosing, the standard WHO and National guidelines for ViPS specify a 3-year interval. * **Option D (Every 4 years):** By the fourth year, the efficacy of the polysaccharide vaccine significantly wanes, leaving the individual susceptible to infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Typhoid Conjugate Vaccine (TCV):** Unlike ViPS, TCV (e.g., Typbar-TCV) is conjugated to a protein carrier (Tetanus Toxoid). This makes it T-cell dependent, providing longer-lasting immunity, and it can be given as early as **6 months of age**. * **Oral Ty21a Vaccine:** A live attenuated vaccine given in a 3-dose schedule (Days 1, 3, and 5). It requires a booster every **3 to 5 years**. * **Minimum Age:** ViPS cannot be given to children **under 2 years** because their immune systems do not respond well to polysaccharide antigens.

Question 297: Which of the following vaccines is routinely administered during pregnancy?

A. Influenza vaccine
B. Oral polio vaccine
C. Tetanus toxoid vaccine (Correct Answer)
D. Rabies vaccine

Explanation: **Explanation:** The administration of vaccines during pregnancy aims to protect both the mother and the newborn through the transplacental transfer of maternal antibodies. **Correct Option: C. Tetanus toxoid vaccine** Under the Universal Immunization Programme (UIP) in India, Tetanus and adult Diphtheria (Td) vaccine is routinely administered to all pregnant women. The primary goal is to prevent **Maternal and Neonatal Tetanus (MNT)**. The schedule involves two doses (Td-1 as early as possible and Td-2 after 4 weeks) or a single booster dose if the woman was immunized within the last 3 years. **Analysis of Incorrect Options:** * **A. Influenza vaccine:** While recommended by some global bodies (like the CDC) to prevent complications, it is not part of the **routine** national immunization schedule for all pregnant women in India unless specific risk factors are present. * **B. Oral polio vaccine (OPV):** OPV is a **Live Attenuated Vaccine**. Live vaccines are generally contraindicated during pregnancy due to the theoretical risk of viral transmission to the fetus. * **D. Rabies vaccine:** This is a post-exposure prophylaxis vaccine. It is administered during pregnancy only if a woman is bitten by a suspected rabid animal. It is not a "routine" antenatal vaccine. **High-Yield NEET-PG Pearls:** * **Live Vaccines Contraindicated:** BCG, MMR, Varicella, and Yellow Fever (unless high risk). * **Safe Vaccines:** All inactivated/killed vaccines and toxoids (Td, Hepatitis B, Inactivated Influenza) are generally safe. * **Td vs TT:** The UIP has replaced Tetanus Toxoid (TT) with **Td (Tetanus and adult Diphtheria)** to provide additional protection against diphtheria. * **Ideal Timing for Tdap:** In some private sectors, a single dose of Tdap (Tetanus, diphtheria, and acellular pertussis) is preferred between 27–36 weeks of gestation to protect the infant from Pertussis.

Question 298: The protective value of a vaccine is stated as 95%. What does this mean?

A. All individuals who receive the vaccine are completely protected.
B. There is a 5% probability of infection among those who have been vaccinated. (Correct Answer)
C. Among the vaccinated population, 95% are immune to the disease.
D. 95% of vaccinated individuals are protected from the disease, while 5% still contract it.

Explanation: ### Explanation **Concept: Vaccine Efficacy and Protective Value** The protective value (or efficacy) of a vaccine refers to the proportionate reduction in disease incidence among vaccinated individuals compared to an unvaccinated group. It is calculated using the formula: **Vaccine Efficacy = [ (ARU – ARV) / ARU ] × 100** *(Where ARU = Attack Rate in Unvaccinated; ARV = Attack Rate in Vaccinated)* When a vaccine has a protective value of 95%, it implies that the vaccine reduces the risk of disease by 95% compared to those not vaccinated. Mathematically, this translates to a **5% residual risk** (probability) of contracting the infection despite being vaccinated. **Analysis of Options:** * **Option B (Correct):** This accurately reflects the statistical probability. If the vaccine is 95% effective, the remaining 5% represents the likelihood of "vaccine failure" or the probability of infection in the vaccinated cohort. * **Option A:** Incorrect. No vaccine provides 100% protection; there is always a margin for primary or secondary vaccine failure. * **Option C:** Incorrect. While 95% may be immune, "protective value" specifically measures the reduction in disease occurrence (incidence) rather than just the presence of antibodies (immunogenicity). * **Option D:** Incorrect. This is a common distractor. It implies a fixed outcome for the population rather than a statistical probability of risk for an individual. **High-Yield Clinical Pearls for NEET-PG:** * **Cold Chain:** The most common cause of reduced vaccine efficacy in India is a break in the cold chain. * **Vaccine Effectiveness:** Refers to how the vaccine performs in "real-world" field conditions, whereas **Efficacy** refers to performance under ideal clinical trial conditions. * **Herd Immunity Threshold:** For most diseases, a protective value/coverage of 80-90% is required to achieve herd immunity, though this varies by the basic reproduction number ($R_0$) of the pathogen.

Question 299: What is the total dose of Vitamin A given under the National Immunisation Schedule?

A. 1.6 million IU
B. 1.7 million IU (Correct Answer)
C. 1.8 million IU
D. 2.0 million IU

Explanation: The correct answer is **1.7 million IU (Option B)**. ### **Explanation** Under the Universal Immunization Programme (UIP) in India, Vitamin A supplementation is administered to children between **9 months and 5 years** of age to prevent nutritional blindness and reduce child mortality. The total dosage is calculated based on a schedule of **9 doses**: 1. **1st Dose:** Given at 9 months (with Measles/MR vaccine) = **1 lakh IU** (1 ml). 2. **2nd Dose:** Given at 18 months (with MR 2nd dose/DPT booster) = **2 lakh IU** (2 ml). 3. **3rd to 9th Doses:** Administered every 6 months until the age of 5 years. There are 7 such doses, each of **2 lakh IU**. * Calculation: 1 lakh + (8 doses × 2 lakh) = 1 + 16 = **17 lakh IU (1.7 million IU).** ### **Why Other Options are Incorrect** * **Option A (1.6 million IU):** This is a common calculation error if the student forgets to include the first dose given at 9 months. * **Option C (1.8 million IU):** This would imply an extra dose or that the first dose was also 2 lakh IU, which is incorrect. * **Option D (2.0 million IU):** This does not align with the current 9-dose schedule under the National Immunization Schedule. ### **High-Yield Clinical Pearls for NEET-PG** * **Target Age Group:** 9 months to 5 years (Total 9 doses). * **Concentration:** The Vitamin A syrup bottle usually contains 1 lakh IU per ml. * **Minimum Interval:** There must be a minimum gap of **6 months** between two consecutive doses. * **Treatment of Xerophthalmia:** The schedule is different (Day 0, Day 1, and Day 14) with age-specific dosing (1 lakh IU for <6 months, 2 lakh IU for >1 year). * **Public Health Impact:** Vitamin A supplementation reduces all-cause mortality in children by approximately 23-24%.

Question 300: Which of the following vaccines, if contaminated, can cause Toxic Shock Syndrome (TSS)?

A. Measles vaccine (Correct Answer)
B. DPT
C. Hepatitis B
D. Typhoral

Explanation: **Explanation:** **Toxic Shock Syndrome (TSS)** in the context of immunization is a severe, life-threatening complication caused by the contamination of multi-dose vaccine vials with **Staphylococcus aureus**. **Why Measles Vaccine is the Correct Answer:** The Measles vaccine is a **live-attenuated, lyophilized (freeze-dried)** vaccine that requires reconstitution with a diluent. Once reconstituted, the vaccine does not contain any preservative (like thiomersal). If the reconstituted vial is kept at room temperature for more than a few hours (usually >4–6 hours), it becomes an ideal culture medium for *Staphylococcus aureus*. If contaminated, the bacteria produce exotoxins that lead to rapid-onset high fever, vomiting, diarrhea, and circulatory collapse (TSS) in vaccinated children. This is why the Universal Immunization Program (UIP) strictly mandates discarding reconstituted measles/MR vaccines after 4 hours. **Analysis of Incorrect Options:** * **B. DPT:** This is a liquid vaccine that contains **Thiomersal** as a preservative, which inhibits bacterial growth, making TSS highly unlikely. * **C. Hepatitis B:** Like DPT, this is a liquid-form vaccine containing preservatives. * **D. Typhoral:** This is an oral live-attenuated vaccine (Ty21a) administered in capsule form; it does not involve reconstitution or the risk of parenteral staphylococcal contamination. **High-Yield Clinical Pearls for NEET-PG:** * **The "4-Hour Rule":** Reconstituted vaccines (Measles, BCG, JE) must be discarded after 4 hours or at the end of the session, whichever is earlier. * **Most Common Organism:** *Staphylococcus aureus* is the most common cause of vaccine-associated TSS. * **Open Vial Policy:** Note that the WHO Open Vial Policy applies to multi-dose liquid vaccines (DPT, HepB, OPV, TT) but **does not** apply to reconstituted vaccines (Measles, BCG, JE). These must be discarded.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free