Immunization and Vaccine-Preventable Diseases Practice Questions

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

Two live vaccines cannot be given simultaneously.. **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.

Q: Which of the following statements about measles is incorrect?

The infectivity of measles is low.. ### 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.

Q: What are the criteria for measles elimination?

Less than 1/100000 cases. ### 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.

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

Diphtheria-Tetanus-Pertussis (DPT). **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.

Q: What is true about the mumps vaccine?

It has an efficacy of 95%.. **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).

Q: 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?

10 years. **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].

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

96%. **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).

Question 1

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

Accepted Answer

Two live vaccines cannot be given simultaneously.

Answer

Live vaccines should not be administered to a patient with Leukemia.

Answer

Live vaccines engage certain tissues of the body.

Answer

With few exceptions, immunization is generally achieved with a single dose of a live vaccine.

Question 2

Which of the following statements about measles is incorrect?

Accepted Answer

The infectivity of measles is low.

Answer

Koplik's spots are pathognomonic.

Answer

The source of infection is typically a case of measles.

Answer

Measles commonly affects the age group of 1 to 3 years.

Question 3

DPT is contraindicated in which of the following conditions?

Accepted Answer

Progressive neurological illness

Answer

Family history of convulsions

Answer

Acute respiratory tract infection

Answer

Cerebral palsy

Question 4

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

Accepted Answer

Oral Polio Vaccine (OPV)

Answer

Measles, Mumps, and Rubella (MMR) vaccine

Answer

Rabies vaccine

Answer

Influenza vaccine

Question 5

What are the criteria for measles elimination?

Accepted Answer

Less than 1/100000 cases

Answer

Less than 1/1000 cases

Answer

Less than 1/10000 cases

Answer

Less than 1/100 cases

Question 6

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

Accepted Answer

Diphtheria-Tetanus-Pertussis (DPT)

Answer

Measles

Answer

BCG

Answer

Diphtheria-Tetanus (DT)

Question 7

What is true about the mumps vaccine?

Accepted Answer

It has an efficacy of 95%.

Answer

It is a killed vaccine.

Answer

Only one dose is administered.

Answer

It is not combined with other vaccines.

Question 8

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?

Accepted Answer

10 years

Answer

12 years

Answer

15 years

Answer

18 years

Question 9

Which vaccine has the highest efficacy?

Accepted Answer

Measles

Answer

DPT

Answer

Oral typhoid

Answer

Tetanus

Question 10

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

Accepted Answer

96%

Answer

94%

Answer

95%

Answer

97%

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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