Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 201: Which of the following is NOT true for 'Live Vaccines'?

A. Two live vaccines cannot be given simultaneously. (Correct Answer)
B. Live vaccines should not be administered to a patient with Leukemia.
C. Live vaccines engage certain tissues of the body.
D. With few exceptions, immunization is generally achieved with a single dose of a live vaccine.

Explanation: **Explanation:** The correct answer is **A**. This statement is false because **two live vaccines can be administered simultaneously** at different injection sites (e.g., MMR and Varicella). If they are not given on the same day, a minimum interval of **4 weeks** is required to prevent the interferon produced by the first vaccine from interfering with the replication of the second. **Analysis of Options:** * **Option B (True):** Live vaccines are generally **contraindicated in immunocompromised states** (Leukemia, Lymphoma, HIV with CD4 <200, or high-dose steroids) because the attenuated organism can cause disseminated, life-threatening disease. * **Option C (True):** Live vaccines mimic natural infection. They **engage specific body tissues** (e.g., OPV replicates in the intestinal mucosa) to induce both humoral (IgG/IgA) and cell-mediated immunity. * **Option D (True):** Because the organism multiplies within the host, a **single dose** usually provides long-lasting immunity. Exceptions include OPV (requires multiple doses to overcome interference from other enteroviruses) and Rotavirus. **High-Yield Clinical Pearls for NEET-PG:** * **The "4-Week Rule":** If two live parenteral vaccines are not given together, wait 28 days. * **Pregnancy:** All live vaccines are contraindicated in pregnancy (exception: Yellow Fever if the risk of disease outweighs the risk of vaccination). * **Heat Sensitivity:** OPV is the most heat-sensitive vaccine; BCG is the most light-sensitive. * **Exceptions to Single Dose:** Oral Polio Vaccine (OPV) and Rotavirus are live vaccines that require multiple doses.

Question 202: Which of the following statements about measles is incorrect?

A. Koplik's spots are pathognomonic.
B. The source of infection is typically a case of measles.
C. The infectivity of measles is low. (Correct Answer)
D. Measles commonly affects the age group of 1 to 3 years.

Explanation: ### Explanation **Why Option C is the correct answer (Incorrect Statement):** Measles is one of the most highly contagious infectious diseases known to mankind. The infectivity of measles is **extremely high**, not low. It has a **Secondary Attack Rate (SAR) of >90%** among susceptible household contacts. The basic reproduction number ($R_0$) for measles is estimated to be between 12 and 18, meaning one infected individual can spread the virus to 12–18 non-immune people. **Analysis of other options:** * **Option A (Koplik's spots are pathognomonic):** This is a **correct** statement. Koplik’s spots (small white spots on a red background on the buccal mucosa opposite the lower second molars) appear during the pre-eruptive stage and are unique to measles. * **Option B (Source of infection is a case):** This is a **correct** statement. There are no known animal reservoirs or long-term carriers for measles. The infection is spread solely by human cases via respiratory droplets. * **Option D (Affects age group 1 to 3 years):** This is a **correct** statement. In endemic areas with high birth rates, measles primarily affects children aged 6 months to 3 years. Maternal antibodies usually protect the infant for the first 6 months of life. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Period:** From 4 days before to 5 days after the appearance of the rash. * **Incubation Period:** Typically 10 days from exposure to fever and 14 days to rash. * **Vitamin A:** Supplementation is mandatory in measles management to reduce mortality and complications like blindness. * **MC Complication:** Otitis media is the most common complication; however, **Pneumonia** is the most common cause of measles-related death. * **SSPE:** Subacute sclerosing panencephalitis is a rare, delayed, fatal neurological complication occurring years after the initial infection.

Question 203: DPT is contraindicated in which of the following conditions?

A. Family history of convulsions
B. Acute respiratory tract infection
C. Progressive neurological illness (Correct Answer)
D. Cerebral palsy

Explanation: **Explanation:** The DPT vaccine consists of Diphtheria toxoid, Pertussis vaccine, and Tetanus toxoid. The **Pertussis (P)** component is highly reactogenic and is responsible for most contraindications associated with the vaccine. **Why "Progressive Neurological Illness" is the Correct Answer:** The absolute contraindication for the Pertussis component is an evolving or unstable neurological condition (e.g., uncontrolled epilepsy, infantile spasms, or progressive encephalopathy). Administering the vaccine during an active neurological decline can aggravate the condition or make it difficult to distinguish vaccine-induced side effects from the progression of the underlying disease. Vaccination should be deferred until the neurological status has stabilized. **Analysis of Incorrect Options:** * **A. Family history of convulsions:** This is a common distractor. A family history of seizures is **not** a contraindication. Only a personal history of a severe reaction (like encephalopathy) within 7 days of a previous DPT dose is a contraindication. * **B. Acute respiratory tract infection:** Minor illnesses (mild fever, cough, or cold) are **not** contraindications to immunization. Vaccination should only be postponed in cases of severe systemic illness or high-grade fever to avoid diagnostic confusion. * **C. Cerebral palsy:** This is a **static** (non-progressive) neurological deficit. Children with stable neurological conditions like cerebral palsy or Down syndrome should be vaccinated as per the schedule. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindication:** Encephalopathy within 7 days of a previous DPT dose. * **Precautionary Situations:** If a child develops a very high fever (>40.5°C), persistent crying (>3 hours), or collapse (HHE - Hypotonic Hyporesponsive Episode) after the first dose, the Pertussis component should be replaced with **DT (Diphtheria and Tetanus)** in subsequent doses. * **Replacement:** In children older than 7 years, DPT is generally not given; **Td** (Tetanus and adult-strength Diphtheria) is preferred.

Question 204: Which vaccine is contraindicated in a child who is positive for Intestinal Rotavirus (IRV)?

A. Oral Polio Vaccine (OPV) (Correct Answer)
B. Measles, Mumps, and Rubella (MMR) vaccine
C. Rabies vaccine
D. Influenza vaccine

Explanation: ### Explanation **Correct Answer: A. Oral Polio Vaccine (OPV)** **Why OPV is the correct answer:** The primary reason for contraindicating **Oral Polio Vaccine (OPV)** in a child with an active intestinal infection (like Intestinal Rotavirus) is **interference**, rather than safety. OPV is a live-attenuated vaccine that must replicate in the gut lymphoid tissue (Peyer's patches) to induce local (IgA) and systemic immunity. When a child has a concurrent viral gastrointestinal infection, the "interferon effect" or local inflammation caused by the rotavirus can prevent the vaccine virus from colonizing the gut. This leads to **vaccine failure**, as the child will not develop the necessary immune response. In such cases, the dose should be deferred until the diarrhea/infection resolves. **Analysis of Incorrect Options:** * **B. MMR Vaccine:** This is a live-attenuated parenteral vaccine. While it is generally deferred during severe acute febrile illness, a localized intestinal infection does not interfere with its subcutaneous replication or efficacy. * **C. Rabies Vaccine:** This is a killed vaccine. Rabies prophylaxis is **never contraindicated** (even in pregnancy or illness) if there is a potential exposure, as the disease is 100% fatal. * **D. Influenza Vaccine:** Most influenza vaccines are inactivated (injectable). They do not replicate in the gut and are not affected by rotavirus infection. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindications for OPV:** Immunodeficiency states (e.g., HIV with low CD4, hypogammaglobulinemia) and household contacts of immunocompromised individuals (to prevent VAPP). * **The "Interference" Phenomenon:** This is why OPV doses are often repeated in Pulse Polio programs—to overcome interference from other enteroviruses common in tropical climates. * **Rotavirus Vaccine:** Interestingly, while rotavirus *infection* interferes with OPV, the Rotavirus *vaccine* can be co-administered with OPV without significant loss of efficacy.

Question 205: What are the criteria for measles elimination?

A. Less than 1/1000 cases
B. Less than 1/10000 cases
C. Less than 1/100000 cases (Correct Answer)
D. Less than 1/100 cases

Explanation: ### Explanation The correct answer is **C. Less than 1/100,000 cases.** **1. Understanding the Concept:** Measles elimination is defined by the World Health Organization (WHO) as the absence of endemic measles virus transmission in a defined geographical area (e.g., a region or country) for at least 12 months in the presence of a high-quality surveillance system. The quantitative indicator for achieving this status is an annual incidence of **less than 1 confirmed case per 1,000,000 (1 million) population** (excluding imported cases). However, in the context of standard public health metrics often tested in exams, this is expressed as **<1 per 100,000 population** when referring to the threshold of "very low incidence" required to sustain elimination. **2. Analysis of Incorrect Options:** * **Options A, B, and D:** These values (1/1,000, 1/10,000, and 1/100) represent much higher incidence rates. At these levels, the virus would still be considered endemic or in an outbreak phase, failing to meet the stringent criteria for elimination which requires interrupting the chain of transmission almost entirely. **3. High-Yield Clinical Pearls for NEET-PG:** * **Measles Eradication vs. Elimination:** Eradication refers to global zero; elimination refers to regional zero. * **Surveillance Indicator:** A "Non-measles febrile rash illness rate" of at least **2 per 100,000** is required to prove that the surveillance system is sensitive enough to detect cases. * **Vaccination Target:** To achieve herd immunity and elimination, **≥95% coverage** with two doses of a measles-containing vaccine (MCV1 and MCV2) is necessary. * **Vitamin A:** Always remember that Vitamin A supplementation (2 doses, 24 hours apart) is a critical part of measles management to reduce mortality.

Question 206: Which disease is prevented by giving a booster dose to a 5-6 year old child?

A. Measles
B. BCG
C. Diphtheria-Tetanus (DT)
D. Diphtheria-Tetanus-Pertussis (DPT) (Correct Answer)

Explanation: **Explanation:** The correct answer is **Diphtheria-Tetanus-Pertussis (DPT)**. Under the National Immunization Schedule (NIS) in India, the **DPT 2nd Booster** is specifically administered at **5–6 years of age**. This dose is crucial because the immunity derived from the primary series (at 6, 10, and 14 weeks) and the 1st booster (at 16–24 months) begins to wane by school entry age. Providing this booster ensures robust protection against Diphtheria, Tetanus, and Pertussis during the early school years. **Analysis of Incorrect Options:** * **Measles (A):** Under the NIS, the first dose is given at 9 completed months and the second dose (as MR vaccine) at 16–24 months. There is no routine booster scheduled at 5–6 years. * **BCG (B):** This is administered at birth (or up to 1 year if missed). Repeat BCG or booster doses are not recommended by the WHO or the Government of India, regardless of Mantoux status. * **Diphtheria-Tetanus (DT) (C):** DT is used as a replacement for DPT only in children who have a contraindication to the Pertussis component (e.g., progressive neurological disorders). It is not the standard vaccine for the general population at this age. **High-Yield NEET-PG Pearls:** * **DPT vs. Td:** DPT is given up to 7 years of age. For children older than 7, the **Td (Tetanus and adult-dose Diphtheria)** vaccine is used because the full-strength Pertussis and Diphtheria components in DPT can cause severe local reactions in older children. * **School Entry Vaccine:** The 5–6 year DPT booster is often referred to as the "school entry" vaccine. * **Recent Change:** Note that the 10-year and 16-year doses, previously TT (Tetanus Toxoid), have now been replaced by **Td** to maintain diphtheria immunity in the population.

Question 207: What is true about the mumps vaccine?

A. It is a killed vaccine.
B. It has an efficacy of 95%. (Correct Answer)
C. Only one dose is administered.
D. It is not combined with other vaccines.

Explanation: **Explanation:** **Correct Option (B): It has an efficacy of 95%.** The mumps vaccine contains the live-attenuated **Jeryl Lynn strain** (most common globally). A single dose provides approximately 80% protection, but after the recommended **two-dose schedule**, the vaccine efficacy increases to about **95%**. This high level of seroconversion is essential for maintaining herd immunity and preventing outbreaks in congregate settings. **Analysis of Incorrect Options:** * **A. It is a killed vaccine:** This is incorrect. The mumps vaccine is a **Live Attenuated Viral Vaccine**. Like most viral vaccines in the routine schedule (except IPV and Hepatitis B), it uses a weakened form of the virus to induce a robust immune response. * **C. Only one dose is administered:** Incorrect. Under the current Universal Immunization Programme (UIP) and IAP guidelines, **two doses** are recommended (usually as MMR/MR) at 9 months and 16–24 months to ensure long-term immunity. * **D. It is not combined with other vaccines:** Incorrect. It is almost always administered as part of a combination vaccine, such as **MMR** (Measles, Mumps, Rubella) or **MMRV** (adding Varicella). **High-Yield Clinical Pearls for NEET-PG:** * **Strain:** The Jeryl Lynn strain is the gold standard; other strains include Urabe (linked to higher rates of aseptic meningitis) and Leningrad-3. * **Storage:** It is heat-sensitive and must be stored at **+2°C to +8°C** (Cold Chain). * **Contraindication:** Being a live vaccine, it is contraindicated in **pregnancy** and **severely immunocompromised** individuals. * **Complication:** While the vaccine is safe, the most common complication of the *disease* itself in post-pubertal males is **orchitis** (usually unilateral).

Question 208: For the prevention of Yellow fever, a single vaccination with 17D non-pathogenic strain of virus gives full protection to the individual for at least how many years?

A. 10 years (Correct Answer)
B. 12 years
C. 15 years
D. 18 years

Explanation: **Explanation:** The correct answer is **10 years (Option A)**. This is based on the International Health Regulations (IHR) regarding the validity of the International Certificate of Vaccination or Prophylaxis [1]. **1. Why 10 years is correct:** The Yellow Fever vaccine (17D strain) is a live-attenuated vaccine. Traditionally, the immunity provided by a single dose was considered to last for 10 years. Under the IHR, the certificate of vaccination becomes valid **10 days** after primary vaccination and remains valid for a period of **10 years** [1]. While the WHO updated its position in 2014 stating that a single dose provides life-long immunity, for the purpose of international travel and standard NEET-PG questions based on IHR guidelines, the "10-year" rule remains the benchmark for re-vaccination and certificate validity. **2. Why other options are incorrect:** * **Options B, C, and D (12, 15, 18 years):** These timeframes do not correspond to any established public health guidelines or clinical milestones for Yellow Fever immunization. There is no physiological or regulatory basis for these specific durations in medical literature. **3. High-Yield Clinical Pearls for NEET-PG:** * **Strain:** 17D strain (grown in chick embryos). * **Type:** Live attenuated vaccine. * **Route & Dose:** 0.5 ml, Subcutaneous. * **Validity:** Starts 10 days after vaccination; lasts for 10 years (as per IHR) [1]. * **Contraindications:** Infants < 6 months, egg allergy, thymic disorders, and symptomatic HIV/immunocompromised states. * **Cold Chain:** Stored at +2°C to +8°C (must be protected from light). * **India Specific:** India is a "Yellow Fever receptive area" (Aedes aegypti is present [1], but the virus is not). Strict quarantine is mandatory for travelers arriving from endemic zones without a valid certificate [2].

Question 209: Which vaccine has the highest efficacy?

A. Measles (Correct Answer)
B. DPT
C. Oral typhoid
D. Tetanus

Explanation: **Explanation:** The efficacy of a vaccine refers to the percentage reduction in disease incidence among vaccinated individuals compared to unvaccinated individuals under ideal conditions. **Why Measles is the Correct Answer:** Measles vaccine (Live Attenuated) is one of the most effective vaccines available. A single dose administered at 9 months provides approximately 85% protection, but with the **second dose**, the efficacy increases to **95–99%**. Because it is a live vaccine, it mimics a natural infection and induces a robust, long-lasting immunological memory. **Analysis of Incorrect Options:** * **DPT:** This is a combination vaccine. While the Tetanus component is highly effective, the **Pertussis** component (especially the older whole-cell version) has a lower and waning efficacy, typically ranging from 70–85%. * **Oral Typhoid (Ty21a):** This live-attenuated vaccine has a moderate efficacy of approximately **50–80%**. It requires multiple doses and boosters every few years, making it significantly less effective than the Measles vaccine. * **Tetanus:** Tetanus toxoid is highly effective (nearly 100% after a full primary series). However, in the context of standard NEET-PG competitive benchmarking, **Measles** is traditionally cited as the vaccine with the highest clinical efficacy among the options provided, particularly when considering the impact of two doses on population immunity. **High-Yield Clinical Pearls for NEET-PG:** * **Highest Efficacy:** Measles (>95% after 2 doses). * **Lowest Efficacy:** Cholera vaccine (approx. 50%) and BCG (highly variable, 0–80%). * **Cold Chain Sensitivity:** Polio (OPV) is the most heat-sensitive vaccine; Tetanus is the most heat-stable. * **Measles Vaccine Strain:** Edmonston-Zagreb strain is commonly used in India. * **Reconstitution:** Measles vaccine must be used within 4 hours of reconstitution; otherwise, it loses potency and risks *Staphylococcus aureus* contamination (Toxic Shock Syndrome).

Question 210: What is the recommended minimum immunization coverage to ensure measles eradication?

A. 94%
B. 95%
C. 96% (Correct Answer)
D. 97%

Explanation: **Explanation:** The correct answer is **96% (Option C)**. **1. Understanding the Concept:** Measles is one of the most highly infectious diseases known to mankind, with a Basic Reproduction Number (**$R_0$**) ranging between **12 and 18**. To achieve "Herd Immunity" and interrupt the transmission of such a contagious virus, a very high percentage of the population must be immune. The formula for the **Herd Immunity Threshold (HIT)** is $1 - (1/R_0)$. For Measles, using an $R_0$ of 15-18, the calculated threshold required to stop the spread is approximately **92-95%**. However, because vaccine efficacy is not 100%, the **programmatic coverage** required to ensure eradication (interruption of indigenous transmission) is set at a minimum of **96%**. **2. Analysis of Options:** * **Option A (94%) & B (95%):** While 95% is often cited as the threshold for "elimination" in specific regions, it is considered the lower limit. For global **eradication**, where the goal is to drive the incidence to zero permanently, a more stringent target of $\geq$96% is recommended by public health authorities to account for pockets of under-vaccination. * **Option D (97%):** While higher coverage is always better, 96% is the scientifically accepted "minimum" benchmark for eradication. **3. High-Yield Clinical Pearls for NEET-PG:** * **Measles Vaccine:** It is a live-attenuated vaccine (Edmonston-Zagreb strain in India). * **National Immunization Schedule (NIS):** 1st dose at 9 completed months (MR), 2nd dose at 16–24 months (MR). * **Cold Chain:** Measles vaccine is highly heat-sensitive and must be stored at +2°C to +8°C (though it can be frozen at -20°C for long-term storage). * **Reconstitution:** Once reconstituted, it must be used within **4 hours**; otherwise, it must be discarded due to the risk of Toxic Shock Syndrome (Staphylococcal 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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