Immunization and Vaccine-Preventable Diseases Practice Questions

Q: Which of the following statements is NOT true about the Inactivated Polio Vaccine (IPV)?

It cannot be given in an AIDS patient.. **Explanation:** The core concept tested here is the safety profile of **Killed (Inactivated) vs. Live Attenuated vaccines** in immunocompromised individuals. **Why Option B is the correct answer (The False Statement):** Inactivated vaccines, like IPV, do not contain live organisms; therefore, they cannot replicate or cause disease in the recipient. Consequently, **IPV is safe and indicated for immunocompromised individuals**, including those with AIDS, symptomatic HIV, or those on immunosuppressive therapy. In contrast, the Oral Polio Vaccine (OPV) is a live vaccine and is strictly contraindicated in these patients due to the risk of Vaccine-Associated Paralytic Poliomyelitis (VAPP). **Analysis of Incorrect Options:** * **Option A:** Under the current National Immunization Schedule (NIS) in India, the **Fractional IPV (fIPV)** is administered in 3 doses (6, 14 weeks, and 9 months). However, the global **Sequential Polio Vaccination Schedule** or specific catch-up schedules often involve 4 doses to ensure full seroconversion, making this a plausible true statement in a general clinical context. * **Option C:** IPV is indeed a **killed vaccine**, produced by inactivating wild-type poliovirus strains (Mahoney, MEF-1, and Saukett) using formaldehyde. * **Option D:** IPV was developed by **Jonas Salk** in 1955, hence it is universally known as the Salk vaccine (whereas OPV is the Sabin vaccine). **NEET-PG High-Yield Pearls:** * **Route:** fIPV is given **Intradermal (ID)** on the right upper arm; full-dose IPV is given **Intramuscular (IM)**. * **VAPP & VDPV:** These are risks associated only with OPV, never with IPV. * **Herd Immunity:** IPV provides excellent individual (humoral) immunity but poor intestinal (mucosal) immunity compared to OPV; thus, it does not effectively stop community transmission.

Q: Which of the following vaccines is the most effective?

Measles vaccine. ### 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. **1. Why Measles Vaccine is the Correct Answer:** The Measles vaccine (live attenuated Edmonston-Zagreb or Schwarz strain) is one of the most potent immunizing agents. A single dose administered at 9 months provides approximately 85% protection, but a second dose (given at 16–24 months) increases the **efficacy to >95–99%**. It produces a long-lasting, almost lifelong immunity that mimics natural infection. **2. Analysis of Incorrect Options:** * **Tetanus Toxoid (TT):** While highly effective (approx. 95% after a full course), it is a toxoid, not a live vaccine. It requires multiple doses and periodic boosters to maintain protective antibody levels, as immunity wanes over time. * **Oral Polio Vaccine (OPV):** The efficacy of OPV varies significantly by geography. In developing countries, interference from other enteroviruses and malnutrition can drop its efficacy per dose to as low as 70–80%, requiring multiple pulses for community protection. * **BCG:** This is the least predictable vaccine in the list. While it is effective against severe forms of childhood tuberculosis (Miliary and Meningeal TB), its efficacy against adult pulmonary TB ranges from **0% to 80%** depending on the study and region. **3. NEET-PG High-Yield Pearls:** * **Most Heat Sensitive Vaccine:** OPV (requires -20°C for long-term storage). * **Most Heat Resistant Vaccine:** Tetanus Toxoid. * **Cold Chain:** Measles and BCG (diluted) are also highly heat-sensitive and must be protected from light. * **Efficacy vs. Effectiveness:** Efficacy is "ideal world" (RCTs); Effectiveness is "real world" (field conditions). * **Herd Immunity Threshold:** For Measles, it is exceptionally high (95%) due to its high $R_0$ (12–18).

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

Measles vaccine. **Explanation:** **Toxic Shock Syndrome (TSS)** following immunization is a severe, life-threatening condition primarily caused by the contamination of multi-dose vaccine vials with **Staphylococcus aureus**. 1. **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 vial is kept at room temperature for several hours, it becomes an ideal culture medium for *Staphylococcus aureus*. If contaminated needles are used or if the reconstituted vial is used beyond the recommended 4–6 hours, the bacteria multiply and produce exotoxins, leading to TSS in the vaccine recipients. 2. **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:** This is also a liquid recombinant vaccine containing preservatives; it does not require reconstitution, reducing the risk of contamination during handling. * **D. Typhoral:** This is an oral live-attenuated vaccine (Ty21a). Since it is administered via the gastrointestinal route and not parenterally, it does not cause systemic Toxic Shock Syndrome associated with injection site contamination. **High-Yield Clinical Pearls for NEET-PG:** * **The 4-Hour Rule:** According to the Open Vial Policy, reconstituted vaccines like Measles, BCG, and JE must be discarded after **4 hours** (or at the end of the session) to prevent TSS. * **Clinical Presentation:** TSS post-measles vaccination typically presents within a few hours with high fever, vomiting, watery diarrhea, and rapid progression to hypotension/shock. * **Most Common Organism:** *Staphylococcus aureus* is the most common cause of vaccine-associated TSS.

Q: Which of the following Oral Polio Vaccine (OPV) vials are usable?

Only vials 1 and 2. ***Only vials 1 and 2*** - **VVM stages 1 and 2** are usable for OPV as the **inner square remains lighter than or equal to the outer circle**, indicating the vaccine is still potent. - These stages represent acceptable **heat exposure levels** where the vaccine maintains its effectiveness and can be safely administered. *Only vial 1* - This option excludes **vial 2**, which is also usable according to **VVM stage 2** criteria where the inner square is still lighter than or equal to the outer circle. - **VVM stage 2** vaccines are perfectly safe and effective, so excluding vial 2 would result in unnecessary vaccine wastage. *Only vials 1, 2, and 3* - **VVM stage 3** shows the **inner square darker than the outer circle**, indicating excessive heat exposure and loss of vaccine potency. - **Stage 3 vaccines** should be **discarded immediately** as they may not provide adequate immunization and could compromise vaccination programs. *Only vials 3 and 4* - **VVM stages 3 and 4** both show **inner squares darker than the outer circle**, indicating the vaccines have been exposed to excessive heat and are no longer effective. - These vaccines should be **discarded immediately** and never administered as they will not provide protection against poliomyelitis.

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

Day 0, 3, 7. ### 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.

Q: A 3-year-old, completely unimmunized child presents to a primary health center immunization clinic for the first time. Which vaccines should be administered?

DT-1, OPV-1, Measles, Vitamin A. ### Explanation This question tests the application of the **National Immunization Schedule (NIS)** guidelines for "catch-up" vaccination in an unimmunized child. **1. Why Option B is Correct:** The core principle here is the age-specific cutoff for certain vaccines: * **BCG:** Can only be given up to **1 year of age**. Since the child is 3 years old, BCG is no longer indicated. * **DPT vs. DT:** The Pertussis component (in DPT) is associated with an increased risk of adverse reactions (like febrile seizures or encephalopathy) as the child grows older. According to the NIS, the Pertussis component is generally not started after age 2. Therefore, for a child between **2 to 7 years**, **DT (Dual Antigen)** is administered instead of DPT. * **OPV, Measles (MR), and Vitamin A:** These are indicated as part of the primary series catch-up. **2. Why Other Options are Wrong:** * **Option A:** Incorrect because it includes BCG (contraindicated after 1 year) and misses essential vaccines like DT and OPV. * **Option C:** Incorrect because it includes both BCG and DPT. DPT is replaced by DT in this age group. * **Option D:** Incorrect because it lists DPT instead of DT. **3. High-Yield NEET-PG Pearls:** * **BCG Cutoff:** Birth to 1 year (0.05ml if 2 years old; use DT instead. * **Measles/MR:** Can be given up to 5 years of age under the routine schedule. * **Vitamin A:** First dose at 9 months (1 lakh IU), subsequent doses every 6 months up to 5 years (2 lakh IU). Total 9 doses. * **JE Vaccine:** Can be given up to 15 years in endemic areas.

Q: Which of the following vaccines does not provide herd immunity?

Rabies. **Explanation:** **Herd immunity** (community immunity) occurs when a large portion of a population becomes immune to a disease, making spread from person to person unlikely. This protects individuals who are not immune (e.g., newborns or the immunocompromised). **Why Rabies is the Correct Answer:** Rabies is a **zoonotic disease** transmitted primarily through the bite of an infected animal (e.g., dogs). There is **no human-to-human transmission** of rabies. Since the vaccine prevents the disease in the individual but does not break a chain of human transmission, it does not provide herd immunity. To achieve herd immunity against rabies, the animal population (dogs) must be vaccinated, not the humans. **Analysis of Incorrect Options:** * **Hepatitis A:** Transmitted via the feco-oral route. Vaccination reduces the viral load and shedding in the community, providing indirect protection to the unvaccinated. * **Measles:** Highly contagious via respiratory droplets. The vaccine is highly effective at preventing transmission, and a high coverage (approx. 95%) is essential for herd immunity. * **Diphtheria:** Transmitted via respiratory droplets. While the vaccine is a toxoid (targeting the toxin), it significantly reduces the carriage of *Corynebacterium diphtheriae* in the pharynx, thereby contributing to herd immunity. **NEET-PG High-Yield Pearls:** * **Vaccines NOT providing Herd Immunity:** Rabies, Tetanus (non-communicable), and Injectable Polio Vaccine (IPV) (provides individual protection but does not prevent intestinal shedding/transmission as effectively as OPV). * **Herd Immunity Threshold:** This depends on the **Basic Reproduction Number ($R_0$)**. The formula is $H = 1 - (1/R_0)$. * **Measles** has the highest $R_0$ (12–18), requiring the highest herd immunity threshold (92–95%).

Q: What is the principle behind supplementary immunisation services for measles immunisation?

All the above. The principle behind **Supplementary Immunization Activities (SIAs)** for measles is to achieve and maintain high levels of population immunity to interrupt virus transmission. In the context of measles elimination, a single dose of vaccine is insufficient due to primary vaccine failure (approx. 15% if given at 9 months) and gaps in routine coverage. **Explanation of the Correct Answer (D):** The strategy relies on three pillars that constitute the "All the above" answer: 1. **Catch-up Immunization (Option B):** This is a one-time nationwide campaign targeting all children (usually 9 months to 14 years) regardless of their previous vaccination or disease history. It aims to rapidly reduce the pool of susceptible individuals. 2. **Follow-up Immunization (Option C):** These are periodic campaigns (every 2–4 years) targeting children born since the last SIA (usually 9 months to 5 years). It prevents the re-accumulation of susceptible children due to routine coverage gaps. 3. **Maintaining Coverage >95% (Option A):** Measles is highly contagious ($R_0$ of 12–18). To achieve "herd immunity" and interrupt transmission, a sustained coverage of $\geq$95% with two doses of measles-containing vaccine (MCV) is mandatory. **High-Yield Clinical Pearls for NEET-PG:** * **Measles Elimination Goal:** Defined as the absence of endemic measles transmission in a region for $\geq$12 months. * **Outbreak Response Immunization (ORI):** This is the fourth component of SIAs, conducted when an outbreak is detected to limit spread. * **Vitamin A:** Always administered during measles SIAs to reduce morbidity and mortality. * **MCV1 & MCV2:** In India, MCV1 is given at 9–12 months and MCV2 at 16–24 months.

Question 1

What is true about polio?

Accepted Answer

Intramuscular injections and increased muscular activity can lead to increased paralysis.

Answer

Paralytic polio is the most common manifestation.

Answer

It causes spastic paralysis.

Answer

The oral polio vaccine is recommended only for children under 3 years of age.

Question 2

Which of the following statements is NOT true about the Inactivated Polio Vaccine (IPV)?

Accepted Answer

It cannot be given in an AIDS patient.

Answer

It is given in 4 doses.

Answer

It is a killed vaccine.

Answer

It is also known as the Salk vaccine.

Question 3

Which of the following vaccines is the most effective?

Accepted Answer

Measles vaccine

Answer

Tetanus toxoid (TT)

Answer

Oral Polio Vaccine (OPV)

Answer

Bacillus Calmette-Guérin (BCG)

Question 4

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

Accepted Answer

Measles vaccine

Answer

DPT

Answer

Hepatitis B

Answer

Typhoral

Question 5

Which of the following Oral Polio Vaccine (OPV) vials are usable?

Accepted Answer

Only vials 1 and 2

Answer

Only vial 1

Answer

Only vials 1, 2, and 3

Answer

Only vials 3 and 4

Question 6

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

Accepted Answer

Day 0, 3, 7

Answer

Day 0, 3, 7, 14, 21, 90

Answer

Day 0, 3, 7, 14, 28, 90

Answer

Day 0, 7, 28

Question 7

How many vaccine vials can a carrier transport daily?

Accepted Answer

8 vials

Answer

4 vials

Answer

10 vials

Answer

16-20 vials

Question 8

A 3-year-old, completely unimmunized child presents to a primary health center immunization clinic for the first time. Which vaccines should be administered?

Accepted Answer

DT-1, OPV-1, Measles, Vitamin A

Answer

BCG, Measles, Vitamin A

Answer

BCG, DPT, DPT-1, OPV-1, Measles, Vitamin A

Answer

DPT-1, OPV, Measles, Vitamin A

Question 9

Which of the following vaccines does not provide herd immunity?

Accepted Answer

Rabies

Answer

Hepatitis A

Answer

Measles

Answer

Diphtheria

Question 10

What is the principle behind supplementary immunisation services for measles immunisation?

Accepted Answer

All the above

Answer

Maintaining coverage above 95%

Answer

Catch-up immunisation

Answer

Follow-up immunisation

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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