Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 81: Which of the following is a live vaccine?

A. Tetanus toxoid (TT)
B. Bacillus Calmette-Guerin (BCG) (Correct Answer)
C. Diphtheria, Pertussis, and Tetanus (DPT)
D. All of the above

Explanation: **Explanation:** The correct answer is **Bacillus Calmette-Guerin (BCG)**. Vaccines are broadly classified based on the nature of the antigen used. **Live attenuated vaccines** contain a version of the living microbe that has been weakened (attenuated) in the lab so it cannot cause disease in immunocompetent individuals but can still induce a robust immune response. BCG is a live attenuated strain of *Mycobacterium bovis* used to prevent severe forms of tuberculosis (like TB meningitis and miliary TB). **Analysis of Options:** * **Tetanus Toxoid (TT):** This is a **toxoid vaccine**. It contains a modified bacterial toxin that has been rendered non-toxic but remains antigenic. * **DPT (Diphtheria, Pertussis, and Tetanus):** This is a **combination vaccine**. It consists of toxoids (Diphtheria and Tetanus) and either killed whole-cell or acellular components (Pertussis). None of these components are live. * **All of the above:** Incorrect, as only BCG is a live vaccine. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Live Vaccines:** "**B**oy **L**ove **C**rime **T**he **M**ayor **G**ave **I**n" (**B**CG, **L**ive Influenza, **C**holera (oral), **T**yphoid (Ty21a), **M**MR, **G**astroenteritis (Rotavirus), **I**PV/OPV - note: only **OPV** is live). * **BCG Administration:** It is given **intradermally** (left deltoid). A characteristic permanent scar forms after 6–12 weeks. * **Diluent for BCG:** Normal Saline (NS). Once reconstituted, it must be used within 3–4 hours or discarded to prevent contamination and loss of potency. * **Contraindication:** Live vaccines should generally be avoided in pregnancy and severely immunocompromised individuals (e.g., symptomatic HIV).

Question 82: Which of the following vaccines should not be given during pregnancy?

A. Hepatitis B vaccine
B. Measles, mumps, rubella (MMR) vaccine (Correct Answer)
C. Typhoid vaccine
D. Cholera vaccine

Explanation: **Explanation:** The core principle in obstetric immunization is that **Live Attenuated Vaccines** are generally contraindicated during pregnancy. This is due to the theoretical risk of the vaccine virus crossing the placenta and causing fetal infection or congenital anomalies. **Why MMR is the Correct Answer:** The MMR vaccine contains live attenuated viruses for Measles, Mumps, and Rubella. The **Rubella** component is of particular concern because the wild-type virus is highly teratogenic, causing Congenital Rubella Syndrome (CRS). While there is no documented case of CRS from the vaccine itself, the theoretical risk necessitates avoiding it during pregnancy. Women are advised to avoid conception for at least 28 days (4 weeks) after receiving the MMR vaccine. **Analysis of Incorrect Options:** * **Hepatitis B Vaccine:** This is a **recombinant (inactivated)** vaccine. It is safe and indicated during pregnancy if the mother is at high risk of infection. * **Typhoid Vaccine:** The injectable Typhoid vaccine (Vi antigen) is an **inactivated/polysaccharide** vaccine and can be given if the risk of exposure is high. (Note: The oral Ty21a vaccine is live and should be avoided). * **Cholera Vaccine:** Modern oral cholera vaccines (OCVs) are **killed/inactivated** and are considered safe for use in pregnant women during outbreaks or in endemic areas. **High-Yield Clinical Pearls for NEET-PG:** * **Safe in Pregnancy:** Tetanus, Diphtheria, Pertussis (Tdap), Influenza (Inactivated), and Hepatitis B. * **Contraindicated in Pregnancy:** MMR, Varicella, Yellow Fever (unless high-risk travel is unavoidable), and BCG. * **Exception:** If a pregnant woman is exposed to Rabies, the **Rabies vaccine** (inactivated) is given as post-exposure prophylaxis because the benefits outweigh the risks. * **Rule of Thumb:** Inactivated vaccines = Safe; Live vaccines = Avoid.

Question 83: Post-exposure vaccination for measles should be done within how many days of exposure?

A. 1 day
B. 2 days
C. 3 days (Correct Answer)
D. 7 days

Explanation: ### Explanation **Correct Answer: C. 3 days** **1. Why 3 days is correct:** Measles has a relatively long incubation period (average 10–14 days). Post-exposure prophylaxis (PEP) with the **Measles vaccine** is effective if administered within **72 hours (3 days)** of exposure. The rationale is that the vaccine-induced immunity develops faster than the natural infection's progression, potentially preventing the disease or significantly reducing its severity. **2. Analysis of Incorrect Options:** * **A & B (1 and 2 days):** While the vaccine is effective if given during this window, "3 days" is the clinically established upper limit for vaccine efficacy in PEP. * **D (7 days):** By day 7, the virus has already undergone significant replication and systemic spread (viremia). The vaccine is no longer effective at this stage. However, **Immunoglobulin (IG)** can be administered up to **6 days** post-exposure for high-risk individuals. **3. High-Yield Clinical Pearls for NEET-PG:** * **Post-Exposure Prophylaxis (PEP) Summary:** * **Measles Vaccine:** Within 3 days (72 hours). * **Human Immunoglobulin (IG):** Within 6 days. Indicated for infants <6 months, pregnant women, and immunocompromised individuals where the vaccine is contraindicated. * **Vitamin A:** Must be administered to all children with acute measles (2 doses, 24 hours apart) to prevent complications like blindness and pneumonia. * **Isolation:** A patient with measles is infectious from **4 days before to 4 days after** the appearance of the rash. * **Secondary Attack Rate (SAR):** Measles has a very high SAR (>90%), making it one of the most contagious diseases.

Question 84: Which of the following does not increase the immunological effectiveness of DPT vaccine?

A. Aluminium phosphate
B. Inactivated whole cell pertussis vaccine
C. Hib polysaccharide conjugated to diphtheria toxoid (Correct Answer)
D. Purified and detoxified components of B. pertussis

Explanation: ### Explanation The core concept tested here is the difference between **adjuvants/synergistic effects** and **carrier-protein conjugation**. **Why Option C is the correct answer:** In a Hib-DPT combination vaccine, the Hib polysaccharide is conjugated to a carrier protein (like diphtheria or tetanus toxoid) primarily to convert the Hib antigen from a T-cell independent to a **T-cell dependent antigen**. This allows infants to develop a memory response against *Haemophilus influenzae* type b. While the toxoid helps the Hib component, the Hib component **does not** increase the immunological effectiveness or potency of the DPT vaccine itself. It is a matter of convenience and expanded coverage, not immunological enhancement of the DPT components. **Analysis of Incorrect Options:** * **Option A (Aluminium phosphate):** This is a classic **adjuvant**. Adjuvants are substances added to vaccines to enhance the body's immune response to the antigen by creating a "depot effect" and stimulating APCs. * **Option B (Inactivated whole cell pertussis):** The whole-cell pertussis component acts as a **built-in adjuvant**. It contains endotoxins and other PAMPs (Pathogen-Associated Molecular Patterns) that significantly boost the immune response to the diphtheria and tetanus toxoids. * **Option D (Purified components of B. pertussis):** Used in acellular pertussis (aP) vaccines, these specific antigens (like pertussis toxoid and filamentous hemagglutinin) still provide the necessary stimulus to ensure an effective immune response against the combined components, though often slightly less reactogenic than whole-cell versions. **NEET-PG High-Yield Pearls:** * **Adjuvants:** DPT is always adsorbed on aluminum phosphate or aluminum hydroxide. **Never freeze** DPT, as freezing destroys the adjuvant structure (Shake Test is used to check this). * **Triple Antigen:** DPT is a mixed vaccine. The pertussis component acts as an adjuvant for the toxoids. * **Hib Conjugation:** The most common carrier proteins for Hib are CRM197 (a non-toxic mutant of diphtheria toxin) or Tetanus Toxoid. * **Route:** DPT is administered **Intramuscularly (IM)** in the anterolateral aspect of the mid-thigh.

Question 85: BCG vaccine should be administered:

A. Immediately after birth (Correct Answer)
B. At 6 months of age
C. At 1 year of age
D. Any time after 1 year of age

Explanation: **Explanation:** **1. Why Option A is Correct:** Under the National Immunization Schedule (NIS) in India, the BCG (Bacillus Calmette-Guérin) vaccine is recommended **at birth** or as soon as possible thereafter. The primary medical rationale is to provide early protection against severe, disseminated forms of childhood tuberculosis, such as **Tubercular Meningitis** and **Miliary Tuberculosis**. Since newborns in endemic areas like India are at immediate risk of exposure, early administration ensures the induction of cell-mediated immunity before natural infection occurs. **2. Why Other Options are Incorrect:** * **Options B, C, and D:** Delaying the vaccine until 6 months or 1 year increases the window of vulnerability for the infant to contract life-threatening TB. While BCG can be given up to the age of **one year** if missed at birth, it is not the "recommended" timing. Beyond one year, the vaccine is generally not administered under the routine NIS because most children in endemic areas would have already been exposed to environmental mycobacteria or *M. tuberculosis*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Type of Vaccine:** Live attenuated (derived from *Mycobacterium bovis*). * **Dose:** 0.05 ml (until 1 month of age); 0.1 ml (beyond 1 month up to 1 year). * **Route & Site:** Strictly **Intradermal** (ID) using an Omega/Tuberculin syringe; Left upper arm (deltoid region). * **Diluent:** Normal Saline (NS). *Note: Distilled water is never used as it causes irritation.* * **The BCG Scar:** Follows a specific sequence: Papule (2-3 weeks) → Pustule/Ulcer (5-6 weeks) → Permanent depressed scar (6-12 weeks). * **Direct BCG:** Giving the vaccine without a prior Mantoux test (standard practice for infants). * **Contraindication:** BCG is contraindicated in individuals with symptomatic HIV infection or severe immunodeficiency.

Question 86: Which of the following is a newer Influenza vaccine?

A. Split-virus vaccine
B. Neuraminidase
C. Live attenuated vaccine
D. Killed vaccine (Correct Answer)

Explanation: ### Explanation The classification of Influenza vaccines is a high-yield topic for NEET-PG. While traditional vaccines have existed for decades, the "newer" generation refers to improvements in formulation and delivery to enhance safety and immunogenicity. **Why the Correct Answer (D) is Right:** In the context of recent advancements, the **Killed (Inactivated) vaccine**—specifically the **Recombinant Influenza Vaccine (RIV)**—is considered the "newer" technology. Unlike traditional methods that grow viruses in chicken eggs, RIV is produced using recombinant DNA technology (e.g., Flublok). This allows for a faster manufacturing process, avoids egg-protein allergies, and provides a precise antigenic match to circulating strains. **Analysis of Incorrect Options:** * **A. Split-virus vaccine:** This is a traditional type of inactivated vaccine where the virus is disrupted by a detergent. It has been in use for many years and is not considered "newer" compared to recombinant or cell-culture technologies. * **B. Neuraminidase:** This is an antigenic surface glycoprotein of the virus, not a vaccine type itself. While it is a target for drugs (Oseltamivir), vaccines primarily target Hemagglutinin (HA). * **C. Live Attenuated Vaccine (LAIV):** Administered intranasally (e.g., FluMist), this has been available since the early 2000s. While more recent than the first whole-virus vaccines, it is older than the latest recombinant killed vaccines. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** Most modern influenza vaccines are **Quadrivalent** (containing two Influenza A and two Influenza B strains). * **Route:** Inactivated vaccines are given **Intramuscularly**, while LAIV is given **Intranasally**. * **Contraindication:** LAIV is contraindicated in pregnancy and immunocompromised individuals; the Inactivated (Killed) vaccine is safe for these groups. * **Antigenic Shift vs. Drift:** Vaccines must be updated annually due to **Antigenic Drift** (minor mutations). **Antigenic Shift** (major changes) leads to pandemics.

Question 87: At the Primary Health Centre (PHC) level, where are vaccines stored?

A. Cold box
B. Deep freezer
C. Ice-lined refrigerator (Correct Answer)
D. Walk-in cold room

Explanation: ### Explanation **Correct Answer: C. Ice-lined refrigerator (ILR)** At the **Primary Health Centre (PHC)** level, the **Ice-lined Refrigerator (ILR)** is the backbone of the cold chain. It is designed to maintain a stable temperature between **+2°C to +8°C**, even during power outages of up to 20 hours, due to the lining of water-filled ice packs or tubes along the cabinet walls. In the Universal Immunization Programme (UIP), ILRs at the PHC level are used to store all vaccines (both heat-sensitive and freeze-sensitive). **Analysis of Incorrect Options:** * **A. Cold Box:** These are insulated containers used for **bulk transportation** of vaccines from district stores to PHCs or for temporary storage during emergencies/maintenance. They are not used for routine permanent storage at the PHC. * **B. Deep Freezer:** At the PHC level, deep freezers are primarily used for **preparing and freezing ice packs**. While they can store OPV and Measles vaccines at the district level (-15°C to -25°C), the ILR is the primary storage unit for all vaccines at the PHC. * **D. Walk-in Cold Room (WIC):** These are large-scale storage facilities located at **Regional or District levels** to supply large populations. They are too large and resource-intensive for the PHC level. **High-Yield Clinical Pearls for NEET-PG:** * **Cold Chain Levels:** * **Regional/State:** Walk-in Coolers (WIC) and Walk-in Freezers (WIF). * **District:** Large ILRs and Deep Freezers. * **PHC:** Small ILRs and Deep Freezers. * **Sub-centre/Session Site:** Vaccine Carriers (last link). * **Storage Rule:** In an ILR, **T**etanus Toxoid (TT/Td), Hep B, and DPT (freeze-sensitive) are kept at the **top**, while OPV and Measles (heat-sensitive) are kept at the **bottom** (the coolest part). * **Thermometer:** A **Dial Thermometer** or **Stem Thermometer** is used to monitor the temperature twice daily.

Question 88: What is defined as 'ring vaccination'?

A. Administered by a ring-shaped machine
B. Given to produce a ring lesion
C. Administered to individuals within a defined radius of a detected case (Correct Answer)
D. Administered to individuals within approximately one mile of a detected case

Explanation: **Explanation:** **Ring Vaccination** is a strategic approach used to inhibit the spread of a highly infectious disease by vaccinating only those who are most likely to be infected. 1. **Why Option C is Correct:** The core concept involves identifying a confirmed case (the "index case") and vaccinating all known contacts, as well as the contacts of those contacts. This creates a "buffer zone" or a "ring" of immune individuals around the infected person, effectively breaking the chain of transmission. The "radius" is defined by the social and geographical network of the case rather than a fixed geometric distance. 2. **Why Other Options are Incorrect:** * **Option A & B:** These are distractors. Ring vaccination refers to a public health strategy, not the physical shape of a machine or the clinical appearance of a lesion (like the "take" in smallpox). * **Option D:** While it mentions a distance, "one mile" is an arbitrary figure. The radius in ring vaccination is dynamic and determined by epidemiological investigation of contacts, not a fixed measurement. **High-Yield Clinical Pearls for NEET-PG:** * **Historical Significance:** Ring vaccination was the primary strategy used by the WHO to **eradicate Smallpox** (Global eradication declared in 1980). * **Recent Application:** It was successfully utilized during the **Ebola** outbreaks in West Africa (using the rVSV-ZEBOV vaccine). * **Comparison:** Unlike **Mass Vaccination** (vaccinating the entire population), Ring Vaccination is more cost-effective and efficient during the "containment" phase of an outbreak. * **Surveillance-Containment:** This strategy relies heavily on a robust "Search and Surveillance" system to identify cases early.

Question 89: A 3-year-old completely unimmunized child presents to an immunization clinic for the first time. What vaccines and supplements should be administered?

A. BCG, Measles, Vitamin-A
B. DT-1, OPV-1, Measles, Vitamin-A
C. BCG, DPT-1, OPV-1, Measles, Vitamin-A
D. DPT-1, OPV-1, Measles, Vitamin-A (Correct Answer)

Explanation: **Explanation:** The management of a "late starter" or unimmunized child depends on the age of presentation and the upper age limits for specific vaccines under the National Immunization Schedule (NIS) in India. **1. Why Option D is Correct:** * **DPT:** Can be given up to 7 years of age. Since the child is 3 years old, DPT-1 is initiated. * **OPV:** Can be given up to 5 years of age. * **Measles (MR):** Can be given up to 5 years of age. * **Vitamin A:** The first dose is usually given at 9 months, followed by doses every 6 months up to 5 years. * **Note on Pentavalent:** While Pentavalent is used in the routine schedule, for a child >1 year, the Hepatitis B and Hib components are generally not prioritized in catch-up unless specifically indicated; however, DPT remains the backbone of the catch-up. **2. Why Other Options are Incorrect:** * **Option A & C (BCG):** BCG is administered at birth. According to NIS guidelines, the **upper age limit for BCG is 1 year**. Since the child is 3 years old, BCG is no longer indicated. * **Option B (DT):** DT (Dual Toxoid) is used as a replacement for DPT only in children **above 7 years of age** (to avoid the systemic reaction of the whole-cell Pertussis component in older children). For a 3-year-old, DPT is the correct choice. **High-Yield NEET-PG Pearls:** * **Upper Age Limits:** * **BCG:** 1 year. * **Rotavirus/Pentavalent/PCV:** 1 year. * **OPV/Measles/DPT:** 5 years (DPT can be extended to 7 years). * **JE Vaccine:** 15 years. * **Vitamin A:** Total 9 doses (1 lakh IU at 9 months; 2 lakh IU every 6 months thereafter until 5 years). Total cumulative dose: 17 lakh IU. * **Injection Site:** If multiple vaccines are given, use different limbs or sites separated by at least 1 inch.

Question 90: Which of the following are live vaccines?

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

Explanation: **Explanation:** The core concept behind this question is the classification of vaccines based on their preparation method. **Live attenuated vaccines** contain a version of the living microbe that has been weakened (attenuated) in the lab so it cannot cause disease in immunocompetent individuals but can still induce a robust immune response. **Why Option C is Correct:** * **BCG (Bacillus Calmette-Guérin):** A live bacterial vaccine derived from *Mycobacterium bovis*. * **OPV (Oral Polio Vaccine/Sabin):** A live attenuated viral vaccine. * **MMR (Measles, Mumps, Rubella):** A combination of three live attenuated viral components. All three components in this option are live vaccines, making it the most accurate choice. **Analysis of Incorrect Options:** * **Option A & B:** These include **TT (Tetanus Toxoid)** and **DPT**. TT is a **toxoid** (inactivated toxin), and the 'P' in DPT (Pertussis) is typically **killed/inactivated** (though acellular versions exist). * **Option D:** While both OPV and MMR are live vaccines, this option is less complete than Option C, which includes BCG. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Live Vaccines:** "**B**oy **R**omeo **G**ive **M**y **L**ove **S**picy **V**ictory **T**onight" (**B**CG, **R**otavirus, **G**umbaro/not human, **M**MR, **L**ive Typhoid [Ty21a], **S**abin/OPV, **V**aricella, **Y**ellow Fever). * **Contraindications:** Live vaccines are generally contraindicated in **pregnancy** and **immunocompromised** states (e.g., HIV with CD4 <200). * **Storage:** Most live vaccines are heat-sensitive and must be stored in the freezer or the coldest part of the ILR (except BCG and Measles after reconstitution). * **Reconstitution:** BCG and Measles vaccines must be used within **4 hours** of reconstitution to prevent Toxic Shock Syndrome (usually caused by *Staph. aureus* contamination).

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

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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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