Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 231: Which vaccine is not indicated during pregnancy?

A. Polio
B. Typhoid
C. Rubella (Correct Answer)
D. TT

Explanation: ### Explanation The core principle in obstetric immunization is the **avoidance of live-attenuated vaccines**. **1. Why Rubella is the Correct Answer:** Rubella is a **live-attenuated virus vaccine**. The primary concern is the theoretical risk of the vaccine virus crossing the placenta and causing **Congenital Rubella Syndrome (CRS)** or fetal infection. Therefore, live vaccines like MMR (Measles, Mumps, Rubella), Varicella, and Yellow Fever are strictly contraindicated during pregnancy. Women are advised to avoid pregnancy for at least 4 weeks (28 days) after receiving the Rubella vaccine. **2. Analysis of Incorrect Options:** * **TT (Tetanus Toxoid):** This is a **toxoid vaccine** and is the most commonly administered vaccine in pregnancy to prevent maternal and neonatal tetanus. It is safe and mandatory. * **Polio:** While the live Oral Polio Vaccine (OPV) is generally avoided, the **Inactivated Polio Vaccine (IPV)** is a killed vaccine and can be administered if the risk of exposure is high (e.g., travel to endemic areas). * **Typhoid:** The **injectable Typhoid vaccine (Vi antigen)** is a subunit (inactivated) vaccine and can be given if there is a significant risk of infection. Only the oral Ty21a (live) vaccine is contraindicated. **3. NEET-PG High-Yield Pearls:** * **Rule of Thumb:** Live vaccines = Contraindicated; Inactivated/Toxoids = Generally safe. * **Exception:** The only live vaccine that can be given during pregnancy under high-risk exposure is **Yellow Fever** (if travel to an endemic zone is unavoidable). * **Postpartum:** The immediate postpartum period is the best time to vaccinate a non-immune woman with the MMR vaccine. * **Influenza:** The inactivated injectable flu vaccine is highly recommended for all pregnant women during any trimester.

Question 232: The Vi polysaccharide vaccine for typhoid is administered by which route?

A. Oral
B. Intramuscular (Correct Answer)
C. Intravenous
D. Intradermal

Explanation: ### Explanation The **Vi polysaccharide vaccine** (e.g., Typhim VI) is a subunit vaccine containing the purified capsular polysaccharide antigen of *Salmonella typhi*. It is administered as a **single-dose intramuscular (IM)** injection, usually into the deltoid muscle. It provides protection by inducing IgG antibodies against the Vi antigen. **Analysis of Options:** * **B. Intramuscular (Correct):** This is the standard route for the Vi polysaccharide vaccine. It is approved for use in individuals aged 2 years and older. * **A. Oral:** This route is used for the **Ty21a vaccine**, which is a live-attenuated liquid or capsule formulation. It requires a schedule of three to four doses on alternate days. * **C. Intravenous:** Vaccines are never administered intravenously as this bypasses the necessary immune processing by local APCs and increases the risk of systemic anaphylaxis. * **D. Intradermal:** While some vaccines (like BCG or Rabies) use this route, the Vi polysaccharide vaccine is specifically formulated for IM use to ensure optimal absorption and immunogenicity. **High-Yield Clinical Pearls for NEET-PG:** * **Age Limit:** Vi polysaccharide vaccine is not effective in children **<2 years** because their immune systems cannot mount a T-cell independent response to polysaccharides. * **Typhoid Conjugate Vaccine (TCV):** This is the preferred vaccine now (e.g., Typbar-TCV). By conjugating the Vi antigen to a protein carrier (Tetanus Toxoid), it becomes immunogenic for infants as young as **6 months** and provides longer-lasting immunity. * **Revaccination:** For the Vi polysaccharide vaccine, a booster dose is recommended every **3 years** for those at continued risk. * **Efficacy:** Both Vi polysaccharide and Ty21a provide approximately 50-80% protection.

Question 233: Meningococcal vaccine is available for all of the following serogroups, except?

A. Group A
B. Group B (Correct Answer)
C. Group C
D. Group Y

Explanation: **Explanation:** The correct answer is **Group B**. The primary challenge in developing a vaccine against **Serogroup B** *Neisseria meningitidis* lies in its capsular polysaccharide structure. Unlike other serogroups, the Group B capsule contains **polysialic acid**, which is structurally identical to the neural cell adhesion molecules (NCAMs) found in human fetal and adult brain tissues. Because of this molecular mimicry, the human immune system recognizes the Group B capsule as "self," making it poorly immunogenic and posing a theoretical risk of autoimmunity if used in a traditional polysaccharide vaccine. **Analysis of Options:** * **Group A, C, Y, and W-135:** These serogroups have distinct capsular polysaccharides that are highly immunogenic. They are included in both the **Quadrivalent Polysaccharide Vaccine** and the **Quadrivalent Conjugate Vaccine** (e.g., MenACWY). These are standard for travelers (Haj pilgrims) and high-risk individuals. * **Group B:** While a "protein-based" vaccine (using recombinant proteins rather than capsular polysaccharides, such as Bexsero or Trumenba) has been developed recently in some countries, it is **not** part of the standard polysaccharide or conjugate vaccines used globally and in India. In the context of standard NEET-PG questions regarding capsular vaccines, Group B is the classic "except." **High-Yield Clinical Pearls for NEET-PG:** 1. **Haj Pilgrims:** Vaccination with the Quadrivalent (A, C, Y, W-135) vaccine is mandatory for pilgrims traveling to Saudi Arabia. 2. **Chemoprophylaxis:** Rifampicin is the drug of choice for close contacts; Ciprofloxacin or Ceftriaxone are alternatives. 3. **Vaccine Type:** Polysaccharide vaccines are ineffective in children <2 years; Conjugate vaccines are preferred for long-term immunity and herd protection.

Question 234: Vaccine-associated paralytic poliomyelitis is suspected if acute flaccid paralysis (AFP) develops within how many days of receipt of oral poliovirus vaccine (OPV)?

A. 30 days
B. 45 days (Correct Answer)
C. 60 days
D. 90 days

Explanation: ### Explanation **Correct Answer: B. 45 days** **1. Understanding the Concept: Vaccine-Associated Paralytic Poliomyelitis (VAPP)** VAPP is a rare adverse event associated with the **Oral Poliovirus Vaccine (OPV)**. It occurs when the live attenuated Sabin strain virus reverts to neurovirulence in the gut of the vaccine recipient or a close contact. According to the World Health Organization (WHO) and National Immunization protocols, VAPP is suspected based on specific temporal criteria: * **Recipient VAPP:** Acute Flaccid Paralysis (AFP) occurring **4 to 30 days** after receiving OPV. * **Contact VAPP:** AFP occurring **4 to 60 days** after exposure to a vaccine recipient. * **The "45-day" Rule:** In the context of surveillance and standard examination questions, the window of **4 to 45 days** is the classically accepted timeframe for a recipient to develop paralysis that is epidemiologically linked to the vaccine dose. **2. Why Other Options are Incorrect:** * **A. 30 days:** While recipient VAPP often manifests within 30 days, the surveillance window extends further to ensure no cases are missed. * **C. 60 days:** This is the timeframe used for **Contact VAPP** (paralysis in an unvaccinated person exposed to a recent vaccinee) rather than the recipient themselves. * **D. 90 days:** This duration is too long; any paralysis occurring after 60–90 days is more likely to be due to a Vaccine-Derived Poliovirus (VDPV) or wild poliovirus rather than the immediate effect of the vaccine dose (VAPP). **3. High-Yield Clinical Pearls for NEET-PG:** * **VAPP vs. VDPV:** VAPP is a rare individual adverse event (1 in 2.7 million doses). **VDPV (Vaccine-Derived Poliovirus)** refers to strains that have mutated significantly and can cause outbreaks in under-immunized communities. * **Risk Factor:** The risk of VAPP is highest with the **first dose** of OPV. * **Diagnosis:** Requires residual weakness at **60 days** post-onset and isolation of the vaccine-type virus from stool samples. * **Prevention:** The shift from OPV to **IPV (Inactivated Poliovirus Vaccine)** in the Universal Immunization Programme (UIP) is primarily to eliminate the risk of VAPP and VDPV.

Question 235: Which of the following statements regarding tetanus is true?

A. A five-dose immunization provides lifelong immunity.
B. Tetanus toxoid provides no protection in the current injury.
C. Tetanus toxoid is useless once 12 hours have passed following injury.
D. Tetanus toxoid and tetanus immunoglobulin may both be administered in suspected tetanus cases. (Correct Answer)

Explanation: **Explanation:** **1. Why Option D is correct:** In cases of tetanus-prone wounds (especially in individuals with uncertain or incomplete immunization history), both **active immunization** (Tetanus Toxoid - TT/Td) and **passive immunization** (Tetanus Immunoglobulin - TIG) are administered. This is known as **simultaneous immunization**. The TIG provides immediate, ready-made antibodies to neutralize circulating toxins, while the TT stimulates the body’s own immune system to produce long-term antibodies. To prevent the TIG from neutralizing the vaccine, they must be administered at **different injection sites** using separate syringes. **2. Why other options are incorrect:** * **Option A:** A five-dose schedule (as per the National Immunization Schedule) provides long-lasting immunity, but it is **not lifelong**. Periodic booster doses (every 10 years) are required to maintain protective antitoxin levels. * **Option B:** Tetanus toxoid is highly effective in the current injury for individuals who are partially immunized or due for a booster, as it triggers an anamnestic (booster) response. * **Option C:** There is no "12-hour cutoff." While early administration is ideal, TT and TIG should be given as soon as possible, regardless of the delay, as the incubation period of tetanus can range from 3 to 21 days. **3. NEET-PG High-Yield Pearls:** * **Incubation Period:** Usually 7–10 days. The shorter the incubation period, the worse the prognosis. * **Neonatal Tetanus:** Also known as the "8th-day disease." * **Herd Immunity:** Tetanus is the only vaccine-preventable disease where **herd immunity does not exist** because the organism (*Clostridium tetani*) is ubiquitous in the soil and not spread person-to-person. * **TIG Dose:** Standard prophylactic dose is 250 units IM (500 units if the wound is heavily contaminated or >24 hours old).

Question 236: Regarding the Hepatitis A vaccine schedule, which of the following is true for all EXCEPT?

A. Recommended at 12 months of age
B. Two doses of killed vaccine given 6 months apart
C. One dose of live vaccine
D. Recommended only in immunocompromised children (Correct Answer)

Explanation: **Explanation:** The Hepatitis A vaccine is recommended for **all children** as part of universal immunization or catch-up vaccination, not just for those who are immunocompromised. In fact, while the killed vaccine is safe for immunocompromised individuals, the **live attenuated vaccine is generally contraindicated** in this group. Therefore, Option D is the "except" statement and the correct answer. **Analysis of Options:** * **Option A:** The first dose of the Hepatitis A vaccine is typically administered at **12 months of age** (range 12–23 months) to ensure the disappearance of maternal antibodies, which could interfere with the immune response. * **Option B:** The **Inactivated (Killed) Vaccine** (e.g., Havrix) requires a **two-dose schedule**, usually given at a 6-month interval (0 and 6 months). It provides long-term immunity. * **Option C:** The **Live Attenuated Vaccine** (e.g., H2 strain) is unique because it is highly immunogenic and requires only a **single dose** to provide adequate protection, making it a cost-effective option in many settings. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Both live and killed vaccines are administered **Intramuscularly (IM)** in the anterolateral thigh or deltoid. * **Post-exposure Prophylaxis (PEP):** Hepatitis A vaccine can be used for PEP if given within **14 days** of exposure in healthy individuals aged 1–40 years. * **Epidemiology:** Hepatitis A is the most common cause of acute viral hepatitis in children in India. * **Contraindication:** Do not give the live vaccine to pregnant women or severely immunocompromised patients.

Question 237: Hepatitis B vaccine in adults should be given as:

A. 0, 1, 2 months
B. 0, 1, 6 months (Correct Answer)
C. 0, 1, 2 years
D. 0, 1, 6 years

Explanation: **Explanation:** The Hepatitis B vaccine is a recombinant DNA vaccine containing HBsAg. In adults, the standard primary immunization schedule follows a **0, 1, and 6-month** regimen. **Why 0, 1, 6 months is correct:** This schedule is designed to optimize the immune response. The first dose (0 month) acts as the primary sensitizer. The second dose (1 month later) triggers a rapid increase in antibody titers. The third dose (6 months after the first) acts as a **booster**, ensuring long-term persistence of antibodies and immunological memory. Achieving an anti-HBs titer of **>10 mIU/mL** is considered protective. **Analysis of Incorrect Options:** * **0, 1, 2 months:** This is an "accelerated schedule" used only in specific high-risk situations (e.g., rapid travel or post-exposure). While it provides quick protection, a fourth dose at 12 months is usually required for long-term immunity. * **0, 1, 2 years & 0, 1, 6 years:** These intervals are far too long. Delaying the third dose by years leaves the individual with suboptimal antibody levels, increasing the risk of infection during the interval. **High-Yield Clinical Pearls for NEET-PG:** * **Route & Site:** Intramuscular (IM). In adults, it must be given in the **deltoid muscle**. It should **never** be given in the gluteal region as the fat reduces vaccine efficacy. * **National Immunization Schedule (NIS):** For infants, it is given at 0 (birth dose), 6, 10, and 14 weeks (as part of the Pentavalent vaccine). * **Storage:** It is highly heat-stable but **freeze-sensitive**. It must be stored at +2°C to +8°C. * **Non-responders:** Approximately 5-10% of adults may not respond to the primary series; they may require a repeat 3-dose series.

Question 238: MMR vaccine is recommended at which age?

A. 9-12 months
B. 2-3 years
C. 10-19 years
D. 15-18 months (Correct Answer)

Explanation: ### Explanation The **MMR (Measles, Mumps, Rubella)** vaccine is a live attenuated vaccine. According to the **Indian Academy of Pediatrics (IAP)** and standard immunization schedules, the first dose of the MMR vaccine is recommended at **15–18 months** of age. **Why 15-18 months is correct:** While the Measles-Rubella (MR) vaccine is given earlier under the National Immunization Schedule (NIS), the specific MMR combination is traditionally administered after the first birthday. By 15 months, maternal antibodies have waned sufficiently to prevent interference with the live vaccine virus, ensuring a robust immune response. **Analysis of Incorrect Options:** * **9-12 months:** This is the age for the **1st dose of Measles/MR vaccine** under the National Immunization Schedule (NIS) in India. MMR is generally not given this early as a routine first dose in private practice/IAP schedules. * **2-3 years:** This is too late for the primary dose. However, the **2nd dose** of MMR is typically given between 4–6 years (or earlier, with a minimum gap of 4-8 weeks). * **10-19 years:** This age group is targeted for Tdap boosters or HPV vaccination, not the primary MMR series. **High-Yield Clinical Pearls for NEET-PG:** * **Route & Dose:** 0.5 ml, Subcutaneous (SC). * **Contraindications:** Pregnancy (risk of Congenital Rubella Syndrome), severe immunosuppression (e.g., low CD4 counts), and history of anaphylaxis to Neomycin or Gelatin. * **NIS vs. IAP:** Under India’s **Universal Immunization Programme (UIP)**, the **MR vaccine** is given at 9 months and 16-24 months. MMR is primarily used in private clinical practice following IAP guidelines. * **Cold Chain:** MMR is highly heat-sensitive and must be stored at +2°C to +8°C; it must be used within 4 hours of reconstitution.

Question 239: A one-year-old child presents for vaccination. What vaccine(s) should be administered?

A. BCG, OPV, Hepatitis B
B. Measles, DPT, OPV, Hib, Hepatitis B (Correct Answer)
C. DPT, OPV, Hib, Hepatitis B
D. DPT, OPV, Hepatitis B

Explanation: **Explanation:** The core concept behind this question is the **National Immunization Schedule (NIS)** of India, specifically focusing on the transition from infancy to the second year of life. **Why Option B is Correct:** At **9 completed months**, the primary series of vaccinations includes the **1st dose of Measles (now MR)** and the **Vitamin A** supplement. However, the question specifies a **one-year-old child**. According to the NIS, if a child has missed their primary doses or is presenting for their scheduled boosters/catch-up, they are eligible for: 1. **Measles (MR):** 1st dose (if missed at 9 months) or preparing for the 2nd dose (16–24 months). 2. **DPT, OPV, Hib, and Hepatitis B:** These are part of the **Pentavalent** series (DPT+HepB+Hib) and the primary OPV series. Under catch-up immunization guidelines, a child presenting at one year should be ensured protection against all these antigens. **Analysis of Incorrect Options:** * **Option A:** BCG, OPV, and Hep B are "at-birth" doses. While BCG can be given up to one year, this option lacks the critical Measles and DPT components required for a one-year-old. * **Options C & D:** These options omit **Measles**, which is the most crucial vaccine introduced at the 9-month mark. Measles remains a leading cause of vaccine-preventable mortality in children under five. **High-Yield NEET-PG Pearls:** * **BCG:** Can be given up to **1 year** of age. If given after 1 month, the dose is 0.1 ml (instead of 0.05 ml). * **Vitamin A:** 1st dose (1 lakh IU) is given at 9 months with MR; subsequent doses (2 lakh IU) are given every 6 months up to 5 years (Total 9 doses/17 lakh IU). * **Pentavalent Vaccine:** Replaced individual DPT and Hep B doses in the primary schedule (6, 10, 14 weeks) to reduce the number of pricks. * **JE Vaccine:** In endemic districts, the 1st dose is administered at 9 months and the 2nd dose at 16–24 months.

Question 240: Which of the following vaccines should not be kept in a freezer?

A. DPT (Correct Answer)
B. Measles
C. OPV
D. All of the above

Explanation: **Explanation:** The correct answer is **A. DPT**. **1. Why DPT is the correct answer:** DPT is an **adsorbed vaccine** that contains aluminum salts (aluminum hydroxide or phosphate) as an adjuvant to enhance the immune response. If these vaccines are frozen, the aluminum salts crystallize and precipitate, leading to the irreversible loss of potency and an increased risk of local reactions (like sterile abscesses) upon injection. Therefore, DPT must be stored in the **refrigerator (2°C to 8°C)** and never in the freezer. Other freeze-sensitive vaccines include TT, DT, Hepatitis B, Pentavalent, and PCV. **2. Why other options are incorrect:** * **B. Measles:** This is a live-attenuated lyophilized (freeze-dried) vaccine. It is relatively heat-stable in its powder form and is not damaged by freezing. In fact, at the district level and above, it is often stored in sub-zero temperatures. * **C. OPV (Oral Polio Vaccine):** This is the **most heat-sensitive** vaccine in the immunization program. To maintain its potency, it must be stored at **-20°C** for long-term storage. Freezing does not damage OPV; it preserves it. **3. High-Yield Clinical Pearls for NEET-PG:** * **Shake Test:** This is a specific test used to determine if an adsorbed vaccine (like DPT or TT) has been damaged by freezing. If the vaccine appears cloudy or has sediments that settle quickly after shaking, it has failed the test and must be discarded. * **Heat Sensitivity Order:** Most sensitive → Least sensitive: **OPV > Measles > BCG > DPT > DT > TT.** * **Storage:** In a standard ILR (Ice-Lined Refrigerator), freeze-sensitive vaccines (DPT, Hep B) are kept at the **top**, while heat-sensitive vaccines (OPV, Measles) are kept at the **bottom** (the coolest part).

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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