Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 31: Which of the following statements are true about Diphtheria?

A. Caused by Gram-negative bacilli
B. Incubation period is 2-5 days
C. Chemoprophylaxis is done with rifampicin
D. A previously immunized asymptomatic household contact should receive a booster dose (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. A previously immunized asymptomatic household contact should receive a booster dose** **1. Why Option D is Correct:** Management of contacts is a high-yield topic in Diphtheria control. For **asymptomatic household contacts** who have been previously immunized, the standard protocol is to administer a **booster dose** of the diphtheria toxoid-containing vaccine to ensure immediate protective immunity. In addition to the booster, they should be monitored for 7 days and given chemoprophylaxis (Erythromycin). **2. Why the Other Options are Incorrect:** * **Option A:** Diphtheria is caused by *Corynebacterium diphtheriae*, which is a **Gram-positive**, non-motile, pleomorphic bacillus (often described as having a "Chinese letter" or cuneiform arrangement). * **Option B:** The incubation period is typically **2 to 5 days**, with a range of 1–10 days. While this option appears correct at first glance, in multiple-choice exams, you must select the *most* accurate clinical management statement. (Note: In some versions of this question, Option B is listed with a different range, but Option D remains the gold-standard management protocol). * **Option C:** The drug of choice for chemoprophylaxis is **Erythromycin** (oral) for 7–10 days or a single dose of Benzathine Penicillin G. Rifampicin is the drug of choice for Meningococcal meningitis prophylaxis, not Diphtheria. **3. High-Yield Clinical Pearls for NEET-PG:** * **Schick Test:** Used to demonstrate the status of immunity against Diphtheria (now largely replaced by antibody titers). * **Virulence:** Produced by an exotoxin; the gene for the toxin is carried by a **Bacteriophage (Beta-phage)**. * **Clinical Hallmark:** A tough, greyish-white **pseudomembrane** that bleeds on touch. * **Culture Media:** Löffler’s serum slope (rapid growth) and Potassium Tellurite agar (black colonies). * **Treatment:** Diphtheria Antitoxin (ADS) must be given immediately on clinical suspicion to neutralize unbound toxin.

Question 32: Which vaccine requires stringent conditions for storage?

A. DPT
B. OPV (Correct Answer)
C. BCG
D. TT

Explanation: ### Explanation **Correct Answer: B. OPV** **Why OPV is the correct answer:** Oral Polio Vaccine (OPV) is the **most heat-sensitive** vaccine in the Universal Immunization Programme (UIP). It is highly thermolabile and requires stringent cold chain maintenance to prevent loss of potency. For long-term storage at the state or regional level, it must be kept at **-20°C**. At the PHC level, it is stored in the Ice-Lined Refrigerator (ILR) at **+2°C to +8°C**. To monitor its heat exposure, OPV vials are equipped with a **Vaccine Vial Monitor (VVM)**, a high-yield clinical marker for NEET-PG. **Why the other options are incorrect:** * **A & D (DPT and TT):** These are **adsorbed vaccines** (containing aluminum salts). They are highly **freeze-sensitive**. While they require refrigeration (+2°C to +8°C), they are much more heat-stable than OPV. Freezing these vaccines causes the adjuvant to precipitate, destroying their potency (confirmed by the **Shake Test**). * **C (BCG):** While BCG is heat-sensitive, it is more stable than OPV in its freeze-dried (lyophilized) form. However, once reconstituted, it becomes highly unstable and must be discarded within 4 hours. **High-Yield NEET-PG Pearls:** 1. **Heat Sensitivity Order (Most to Least):** OPV > Measles/MR > BCG > DPT > DT > TT. 2. **Freeze Sensitivity Order (Most to Least):** Hepatitis B > DPT > TT. 3. **Storage Level:** At the **District level**, all vaccines (including OPV) can be stored for up to 1 month at +2°C to +8°C, but OPV is the only one ideally kept in deep freezers at -20°C for longer durations. 4. **The Shake Test:** Used for DPT, TT, and Hepatitis B to check if they were accidentally frozen. It is **never** done for OPV or BCG.

Question 33: The term "Vaccine" was coined by whom?

A. Louis Pasteur (Correct Answer)
B. Edward Jenner
C. James Lind
D. John Snow

Explanation: **Explanation:** The term **"Vaccine"** was coined by **Louis Pasteur** in 1881. While Edward Jenner performed the first successful vaccination against smallpox using cowpox material, it was Pasteur who proposed the term "vaccine" (derived from the Latin word *vacca*, meaning cow) as a tribute to Jenner’s work. Pasteur extended the concept beyond smallpox to develop vaccines for Anthrax, Chicken Cholera, and Rabies. **Analysis of Incorrect Options:** * **Edward Jenner:** Known as the **"Father of Immunology."** He performed the first vaccination in 1796 using cowpox virus to protect against smallpox. However, he did not coin the general term "vaccine." * **James Lind:** Known as the **"Father of Naval Hygiene."** He conducted the first clinical trial and discovered that citrus fruits (Vitamin C) could cure Scurvy. * **John Snow:** Known as the **"Father of Modern Epidemiology."** He is famous for his work during the 1854 cholera outbreak in London (Broad Street pump) and for being a pioneer in anaesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **Louis Pasteur’s Contributions:** Germ theory of disease, Pasteurization, and development of the **Rabies vaccine**. * **Smallpox:** The only human disease to be globally eradicated (declared by WHO on May 8, 1980). * **Cold Chain:** The most sensitive vaccine to heat is **OPV** (stored at -20°C), while the most heat-stable is **Hepatitis B**. * **First Vaccine:** The first vaccine developed was for Smallpox (Jenner); the first live attenuated viral vaccine was for Yellow Fever (Theiler).

Question 34: The risk of cold chain failure is greatest at which level?

A. Regional level
B. District Level
C. PHC level
D. Subcentre & village level (Correct Answer)

Explanation: **Explanation:** The **cold chain** is a system of transporting and storing vaccines at recommended temperatures from the point of manufacture to the point of use. The risk of cold chain failure is inversely proportional to the level of the health facility; as we move from the national level toward the periphery, the risk increases. **Why Subcentre & Village level is the correct answer:** This is the **last mile** of the cold chain. At this level, vaccines are stored in **vaccine carriers** with four conditioned ice packs, which have a limited cold life (usually 12–48 hours). Unlike higher levels, there is no continuous electrical refrigeration (like ILRs). Furthermore, factors such as extreme ambient temperatures during field transport, lack of specialized supervision, and potential delays in outreach sessions make this level the most vulnerable to temperature excursions. **Analysis of Incorrect Options:** * **Regional & District Levels:** These levels are equipped with **Walk-in Cold Rooms (WICR)** and large **Ice-Lined Refrigerators (ILR)**. They have robust power backups (generators), continuous temperature monitoring, and dedicated cold chain technicians, making the risk of failure relatively low. * **PHC Level:** While more vulnerable than the district level, PHCs are equipped with small ILRs and Deep Freezers. They serve as the storage point for vaccines for about one month. While risks exist, the infrastructure is superior to the portable equipment used at the subcentre level. **High-Yield Clinical Pearls for NEET-PG:** 1. **Most Heat Sensitive Vaccine:** Oral Polio Vaccine (OPV). 2. **Most Heat Resistant Vaccine:** BCG (before reconstitution). 3. **Most Cold/Freeze Sensitive Vaccines:** Hepatitis B, DPT, Pentavalent, and TT (Must never be frozen). 4. **The "Hub" of Cold Chain:** The **ILR (Ice-Lined Refrigerator)** is considered the most important component at the PHC level. 5. **Temperature Monitoring:** Done twice daily. The **Vaccine Vial Monitor (VVM)** is the most important tool to check heat exposure at the user level.

Question 35: Which vaccine is most effective?

A. Cholera
B. Typhoid
C. Yellow fever (Correct Answer)
D. Chicken pox

Explanation: **Explanation:** The effectiveness of a vaccine is measured by its **efficacy rate**, which refers to the percentage reduction in disease incidence among vaccinated individuals under ideal conditions. **Why Yellow Fever is the correct answer:** The Yellow Fever vaccine (17D strain) is considered one of the most effective vaccines ever developed. It is a live-attenuated vaccine that provides **near 100% efficacy** (99% seroconversion). A single dose provides lifelong immunity in most individuals, and international health regulations recognize its validity for life. Its rapid induction of immunity (within 10 days) makes it the gold standard for vaccine effectiveness. **Analysis of Incorrect Options:** * **Cholera:** This vaccine has historically low efficacy (around 50–60%) and provides short-term protection (3–6 months). Even modern oral cholera vaccines (OCV) require two doses and offer limited long-term durability. * **Typhoid:** The injectable Vi polysaccharide vaccine has an efficacy of about 70%, while the oral Ty21a vaccine ranges from 50–80%. Neither approaches the near-perfect protection of Yellow Fever. * **Chickenpox (Varicella):** While highly effective, the varicella vaccine has an efficacy of approximately 85–95%. "Breakthrough varicella" can still occur in vaccinated individuals, though the disease is usually milder. **High-Yield Clinical Pearls for NEET-PG:** * **Strain used:** 17D strain (grown on chick embryo). * **Type:** Live attenuated vaccine. * **Route:** Subcutaneous. * **Validity:** Starts 10 days after vaccination and lasts for **life** (as per WHO amendment to IHR 2016). * **Contraindication:** Not given to infants <6 months, individuals with egg allergy, or symptomatic HIV/immunocompromised states.

Question 36: What is true about polio?

A. Paralytic polio is the most common manifestation.
B. It causes spastic paralysis.
C. Intramuscular injections and increased muscular activity can lead to increased paralysis. (Correct Answer)
D. The oral polio vaccine is recommended only for children under 3 years of age.

Explanation: ### Explanation **1. Why Option C is Correct: Provocation Poliomyelitis** The correct answer refers to a phenomenon known as **Provocation Poliomyelitis**. If a person is already incubating the poliovirus, trauma to a muscle—specifically through **intramuscular (IM) injections** (like DPT) or excessive **muscular activity**—can lead to the localization of paralysis in that specific limb. The trauma causes increased vascularity in the corresponding segment of the spinal cord, allowing the virus to cross the blood-brain barrier more easily at that site. **2. Why the Other Options are Incorrect:** * **Option A:** Paralytic polio is actually the **least common** manifestation (occurring in <1% of infections). Most cases (90–95%) are **asymptomatic/inapparent**, while a small percentage present as "Abortive Polio" (minor flu-like illness). * **Option B:** Polio causes **Flaccid Paralysis**, specifically **Acute Flaccid Paralysis (AFP)**. It involves Lower Motor Neuron (LMN) lesions due to the destruction of anterior horn cells in the spinal cord. Spastic paralysis is characteristic of Upper Motor Neuron (UMN) lesions. * **Option D:** Under the Global Polio Eradication Initiative and National Immunization Schedule, OPV is given at birth (zero dose) and at 6, 10, and 14 weeks, with a booster at 16–24 months. However, during Pulse Polio Immunization (PPI) rounds, it is administered to **all children under 5 years of age**, regardless of previous status. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common strain:** Type 1 is most frequently associated with paralytic outbreaks. * **VAPP vs VDPV:** Vaccine-Associated Paralytic Polio (VAPP) occurs in the vaccine recipient; Vaccine-Derived Poliovirus (VDPV) occurs due to the circulation of the attenuated virus in the community. * **Surveillance:** The "Gold Standard" for polio surveillance is **AFP Surveillance**, requiring two stool samples collected 24 hours apart within 14 days of onset of paralysis. * **Recent Change:** India has switched from Trivalent OPV to **Bivalent OPV** (Types 1 & 3) and introduced **Fractional IPV (fIPV)** to mitigate the risk of Type 2 outbreaks.

Question 37: What is the dose of Oral Polio Vaccine (OPV) given at birth in cases of institutional deliveries?

A. Zero dose OPV (Correct Answer)
B. Initial dose
C. Primary dose
D. First dose

Explanation: **Explanation:** The correct answer is **Zero dose OPV**. In the context of the National Immunization Schedule (NIS), the dose of OPV administered at birth (or as soon as possible within the first 15 days) is specifically termed the "Zero Dose." **Why it is correct:** The term "Zero Dose" is used because this administration does not count toward the primary three-dose series required for basic immunization. Its primary medical objective is to induce **local mucosal immunity** (IgA) in the gut before the infant can be exposed to wild poliovirus or other enteric pathogens. This early priming ensures a more robust immune response when the subsequent primary doses are administered at 6, 10, and 14 weeks. **Why other options are incorrect:** * **Initial/First Dose:** While chronologically the first, these terms are technically incorrect in a public health context. The "First Dose" of OPV is officially recorded as the dose given at **6 weeks** of age along with Pentavalent-1. * **Primary Dose:** This refers to the collective series of doses (OPV 1, 2, and 3) given to achieve seroconversion. The birth dose is considered "pre-primary." **High-Yield Clinical Pearls for NEET-PG:** * **Maximum Age for Zero Dose:** OPV Zero dose can be given up to a maximum of **15 days** after birth. * **Route and Dose:** 2 drops, Orally. * **VVM (Vaccine Vial Monitor):** OPV is the most heat-sensitive vaccine; always check the VVM (inner square should be lighter than the outer circle). * **Type of Vaccine:** OPV (Sabin) is a **Live Attenuated** vaccine, whereas IPV (Salk) is Killed. * **Current Strategy:** India currently uses **bOPV** (Bivalent OPV containing types 1 and 3) in routine immunization, supplemented by Fractional IPV (fIPV) at 6 and 14 weeks.

Question 38: Which of the following best describes the Yellow fever vaccine?

A. Killed vaccine
B. Live attenuated vaccine (Correct Answer)
C. Toxoid
D. Subcellular vaccine

Explanation: The **Yellow Fever vaccine (17D strain)** is a classic example of a **live attenuated vaccine**. It is prepared by serial passage of the virus in chick embryos, which reduces its virulence while maintaining its ability to induce a robust, long-lasting immune response. ### Explanation of Options: * **Option B (Correct):** The 17D strain is a live attenuated virus. It provides exceptionally high efficacy (nearly 100%) and is known for its longevity; a single dose is now considered by the WHO to provide life-long immunity for most travelers. * **Option A (Incorrect):** Killed (inactivated) vaccines (e.g., Salk Polio, Hepatitis A) use heat or chemicals to destroy the pathogen's ability to replicate. The Yellow Fever vaccine must replicate in the host to be effective. * **Option C (Incorrect):** Toxoids are inactivated toxins produced by bacteria (e.g., Tetanus, Diphtheria). Yellow Fever is a viral disease, not a toxin-mediated bacterial one. * **Option D (Incorrect):** Subcellular (subunit) vaccines use only specific fragments of the pathogen (e.g., Hepatitis B surface antigen). The 17D vaccine uses the whole attenuated virus. ### High-Yield Clinical Pearls for NEET-PG: * **Route & Dose:** 0.5 ml, administered **Subcutaneously**. * **Validity:** The International Certificate of Vaccination becomes valid **10 days** after vaccination and lasts for **life**. * **Contraindications:** Infants <6 months, pregnant women (unless in high-risk outbreaks), symptomatic HIV/AIDS, and individuals with **egg hypersensitivity** (as it is grown in chick embryos). * **Cold Chain:** It is highly heat-sensitive and must be stored between **+2°C to +8°C**. * **Strains:** Derived from the wild Asibi strain.

Question 39: Who introduced the smallpox vaccine?

A. Paul Ehrlich
B. Robert Koch
C. Louis Pasteur
D. Edward Jenner (Correct Answer)

Explanation: **Explanation:** **Edward Jenner (Option D)** is the correct answer. In **1796**, Jenner observed that milkmaids who had contracted cowpox (a milder disease) appeared immune to smallpox. He conducted a landmark experiment by inoculating a young boy, James Phipps, with material from a cowpox lesion and later exposing him to smallpox. The boy did not develop the disease. This discovery laid the foundation for modern immunology and led to the eventual global eradication of smallpox in 1980. **Analysis of Incorrect Options:** * **Paul Ehrlich (Option A):** Known as the "Father of Chemotherapy," he discovered the first effective treatment for syphilis (Salvarsan) and proposed the "Side-Chain Theory" of antibody formation. * **Robert Koch (Option B):** A pioneer of bacteriology who discovered the causative agents of Anthrax, Cholera, and Tuberculosis (*Koch’s Bacillus*). He is famous for **Koch’s Postulates**. * **Louis Pasteur (Option C):** Known for the "Germ Theory of Disease" and the process of pasteurization. He developed vaccines for **Rabies, Anthrax, and Fowl Cholera**, but not smallpox. **High-Yield Clinical Pearls for NEET-PG:** * **Smallpox Eradication:** Smallpox is the only human infectious disease to be completely eradicated. * **Last Case:** The last naturally occurring case was reported in **Somalia (1977)**. * **Global Declaration:** The WHO declared the world free from smallpox on **May 8, 1980**. * **Vaccine Type:** The smallpox vaccine used the **Vaccinia virus** (live virus), not the Variola virus. * **Bifurcated Needle:** The specific tool used for the "multiple puncture" vaccination technique.

Question 40: What is the post-exposure prophylaxis schedule for rabies vaccine in a previously immunized person?

A. Day 0, 3, 7, 14, 21, 90
B. Day 0, 3, 7, 14, 28, 90
C. Day 0, 3, 7 (Correct Answer)
D. Day 0, 7, 28

Explanation: ### Explanation **1. Why Option C is Correct:** According to the latest **WHO and National Guidelines (NRCP)**, the post-exposure prophylaxis (PEP) for a person who has been **previously immunized** (documented proof of a complete pre-exposure or post-exposure schedule) consists of only **two booster doses** of a modern cell-culture vaccine (CCV). These are administered intramuscularly or intradermally on **Day 0 and Day 3**. *Note:* While the standard current guideline is Day 0 and 3, older textbooks and some exam patterns still reference the **Day 0, 3, 7** schedule (Option C) as the "re-exposure" protocol. In the context of this specific question, Option C is the most appropriate choice among the provided options, as it reflects the shortened "booster" principle. Crucially, **Rabies Immunoglobulin (RIG) is NOT required** for previously immunized individuals. **2. Why Other Options are Incorrect:** * **Options A & B:** These represent the older 6-dose (Essen) and 5-dose schedules used for **unvaccinated** individuals. A previously immunized person has "immunological memory," so a full course and RIG are unnecessary. * **Option D:** This schedule (0, 7, 28) is the standard **Pre-Exposure Prophylaxis (PrEP)** regimen for high-risk individuals (e.g., veterinarians, lab workers), not a post-exposure protocol. **3. High-Yield Clinical Pearls for NEET-PG:** * **Definition of "Previously Immunized":** Someone who has completed a full PrEP or PEP course with a Cell Culture Vaccine. * **RIG Rule:** Never give RIG to a previously immunized person; it can interfere with the rapid anamnestic (booster) immune response. * **Wound Care:** Immediate flushing of the wound with soap and water for 15 minutes is the most critical first step, regardless of immunization status. * **Intradermal Regimen (Updated):** The standard PEP for **unimmunized** patients is now the **2-2-2-0-0** (Updated Thai Red Cross) regimen: 2 doses on days 0, 3, and 7.

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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