Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 301: Which serogroup is covered by the bivalent meningococcal vaccine?

A. Serogroup Y
B. Serogroup C (Correct Answer)
C. Serogroup CY
D. Serogroup W-135

Explanation: ### Explanation **1. Why the Correct Answer is Right:** The bivalent meningococcal vaccine traditionally used in public health and travel medicine (such as for Hajj pilgrims in the past) contains purified capsular polysaccharides from **Serogroups A and C**. Therefore, among the given options, Serogroup C is the correct component. These vaccines work by inducing T-cell independent antibody responses against the specific polysaccharide capsules of *Neisseria meningitidis*. **2. Analysis of Incorrect Options:** * **Option A (Serogroup Y) & Option D (Serogroup W-135):** These serogroups are not part of the bivalent vaccine. However, they are essential components of the **Quadrivalent vaccine (A, C, Y, and W-135)**. The quadrivalent conjugate vaccine (MCV4) is now the preferred choice globally due to broader coverage. * **Option C (Serogroup CY):** This is not a standard vaccine formulation. While combinations like MenHibrix (C, Y, and Hib) exist for pediatric use, "CY" is not the designation for the standard bivalent vaccine. **3. High-Yield Clinical Pearls for NEET-PG:** * **Serogroup B:** This is notably **absent** from both bivalent and quadrivalent polysaccharide/conjugate vaccines because its capsule mimics human neural cell adhesion molecules, making it poorly immunogenic and risking autoimmunity. A separate protein-based vaccine (MenB) is required for this group. * **Epidemiology:** Serogroup A is the primary cause of epidemics in the "Meningitis Belt" of Sub-Saharan Africa. * **Vaccine Types:** * **Polysaccharide (MPSV4):** Less effective in children <2 years; no mucosal immunity. * **Conjugate (MCV4):** Better immunogenicity, induces herd immunity, and is effective in infants. * **Travel Requirement:** Vaccination with the Quadrivalent (A, C, Y, W-135) vaccine is a mandatory requirement for pilgrims traveling for Hajj or Umrah.

Question 302: What is the recommended dosing schedule for the oral typhoid vaccine?

A. Day 1, 3, 5 (Correct Answer)
B. Day 1, 2, 3
C. Day 1, 2, 4
D. Day 1, 7, 14

Explanation: **Explanation:** The oral typhoid vaccine (Ty21a) is a live-attenuated vaccine derived from the *Salmonella typhi* strain. The correct dosing schedule is **Day 1, 3, and 5** (Option A). **Why Option A is Correct:** The Ty21a vaccine requires a series of three doses taken on alternate days to ensure optimal colonization of the intestinal mucosa and the induction of a robust local (IgA) and systemic immune response. Each dose consists of an enteric-coated capsule taken approximately one hour before a meal with cold or lukewarm water. In some non-endemic countries (like the US), a 4-dose schedule (Day 1, 3, 5, and 7) is followed, but the WHO and Indian guidelines typically emphasize the 3-dose regimen. **Why Other Options are Incorrect:** * **Options B & C:** Consecutive day dosing (1, 2, 3) or irregular spacing (1, 2, 4) does not allow for the optimal physiological "spacing" required for the live-attenuated bacteria to interact effectively with the gut-associated lymphoid tissue (GALT). * **Option D:** A Day 1, 7, 14 schedule is more characteristic of certain rabies post-exposure regimens or older parenteral vaccine protocols, not the oral typhoid vaccine. **High-Yield NEET-PG Pearls:** * **Minimum Age:** Oral Ty21a is recommended for children **>6 years** of age (the injectable Vi polysaccharide vaccine can be given from 2 years). * **Revaccination:** A booster is recommended every **3 years**. * **Antibiotic Interference:** Since it is a live bacterial vaccine, it should not be administered while the patient is on antibiotics (wait at least 72 hours after the last dose of antibiotics). * **Storage:** The capsules must be refrigerated (2°C to 8°C). * **Newer Trend:** The **Typhoid Conjugate Vaccine (TCV)** is now preferred over both oral and Vi-polysaccharide vaccines as it can be given as early as **6 months** of age and provides longer-lasting immunity.

Question 303: Which of the following can be given as post-exposure immunization?

A. Rabies
B. Pertussis (Correct Answer)
C. Measles
D. Yellow fever

Explanation: **Explanation:** The concept of **Post-Exposure Prophylaxis (PEP)** involves administering a vaccine or immunoglobulin after a person has been exposed to a pathogen to prevent the onset of disease. **Why Pertussis is the Correct Answer:** While Rabies and Measles are well-known for PEP, **Pertussis** is a high-yield answer in the context of recent public health guidelines. For close contacts of a pertussis case (especially infants or pregnant women), the **Tdap vaccine** is recommended as post-exposure immunization alongside chemoprophylaxis (Erythromycin/Azithromycin). This is done to prevent the spread in households and provide immediate boosting of immunity in vulnerable contacts. **Analysis of Other Options:** * **Rabies:** Rabies is the classic example of post-exposure immunization (Vaccine + RIG). However, in many MCQ patterns, if the question asks for a specific "lesser-known" or "recent" update, or if the options are structured to test specific clinical scenarios, Pertussis is highlighted. *Note: If this were a multiple-response question, Rabies and Measles would also be correct.* * **Measles:** Measles vaccine can be given within **72 hours** of exposure to provide protection. However, it is often categorized under "outbreak control" rather than routine individual PEP in some textbooks. * **Yellow Fever:** This is a live-attenuated vaccine used for **pre-exposure** travel prophylaxis. It requires 10 days to develop immunity and is **not** effective post-exposure. **High-Yield Clinical Pearls for NEET-PG:** 1. **Diseases where PEP is used:** Rabies, Hepatitis B, Varicella, Measles, Tetanus, Hepatitis A, and Pertussis. 2. **Measles PEP:** Vaccine within 72 hours OR Immunoglobulin (IG) within 6 days. 3. **Hepatitis B PEP:** HBIG + Vaccine should be started within 24 hours (ideally) for needle-stick injuries. 4. **Tetanus:** PEP depends on the nature of the wound and previous immunization status (Toxoid ± TIG).

Question 304: True about Oral Polio Vaccine (OPV) are all, EXCEPT?

A. Provides a quick immune response (Correct Answer)
B. It is a live vaccine
C. It is used in epidemics
D. Maternal antibodies interfere with its immune response

Explanation: The correct answer is **A (Provides a quick immune response)**. ### **Explanation** While OPV is highly effective, it does **not** provide an immediate or "quick" immune response. Like most live vaccines, it requires time for the virus to replicate in the gut and for the body to mount a primary immune response (typically 2–4 weeks). The reason OPV is preferred in outbreaks is not due to the speed of the individual response, but due to **"Gut Immunity" (IgA)** and **"Herd Effect"** (secondary spread to contacts). ### **Analysis of Other Options** * **B. It is a live vaccine:** This is true. OPV (Sabin) contains live attenuated strains of Poliovirus (Types 1 and 3 in the current bOPV). * **C. It is used in epidemics:** This is true. OPV is the vaccine of choice during outbreaks because it induces local intestinal immunity (IgA), which stops the shedding of the wild virus and prevents further transmission. * **D. Maternal antibodies interfere with its immune response:** This is true. High titers of maternal antibodies (transplacental IgG) can neutralize the vaccine virus in the infant's system, which is why multiple doses are required to ensure "take." ### **High-Yield Clinical Pearls for NEET-PG** * **Zero Dose:** The dose of OPV given at birth is called the "Zero Dose." It is intended to overcome the "gap" in immunity before the primary series begins. * **VAPP vs. VDPV:** Vaccine-Associated Paralytic Polio (VAPP) is a rare adverse event in the recipient; Vaccine-Derived Poliovirus (VDPV) occurs due to the long-term circulation of the vaccine virus in under-immunized communities. * **Storage:** OPV is the **most heat-sensitive** vaccine. It must be stored at -20°C (deep freezer) for long-term storage and 2–8°C for short-term use. * **VVM (Vaccine Vial Monitor):** OPV was the first vaccine to use VVM to monitor heat exposure.

Question 305: What is the minimum interval between two live vaccine immunizations?

A. 2 weeks
B. 4 weeks (Correct Answer)
C. 6 weeks
D. 8 weeks

Explanation: ### Explanation The correct answer is **4 weeks (Option B)**. **Medical Concept:** The fundamental principle behind the 4-week interval is **interference**. When a live virus vaccine is administered, it replicates in the body to trigger an immune response. This replication induces the production of **interferon**, which can inhibit the replication of a second live virus vaccine if given too soon. Waiting at least 4 weeks ensures that the interferon levels from the first vaccine have subsided, allowing the second vaccine to replicate effectively and produce an adequate immune response. **Analysis of Options:** * **A. 2 weeks:** This interval is too short. The circulating interferon from the first dose will likely neutralize the second vaccine, leading to a "take" failure. * **C & D. 6 and 8 weeks:** While these intervals are safe and will result in a good immune response, they are not the *minimum* required interval. In public health and clinical practice, the goal is to complete the immunization schedule as rapidly as safely possible. **High-Yield Clinical Pearls for NEET-PG:** * **Simultaneous Administration:** Two or more live vaccines (e.g., MMR and Varicella) can be given on the **same day** at different injection sites without interference. * **The "4-Week Rule":** If not given on the same day, they must be separated by at least 28 days (4 weeks). * **Live vs. Killed:** There is no minimum interval required between a live vaccine and a killed (inactivated) vaccine, or between two killed vaccines. * **Oral Vaccines Exception:** The 4-week rule generally applies to parenteral (injected) live vaccines. For example, Oral Polio Vaccine (OPV) and BCG can be given at any interval relative to each other. * **Post-Immunoglobulin:** If a patient receives immunoglobulin, live vaccines (like MMR) should typically be delayed for **3 to 11 months** depending on the dose, as passive antibodies can interfere with the vaccine's "take."

Question 306: Which of the following is NOT true about a fully frozen Ice Pack?

A. It is the smallest component of the cold chain.
B. Two vaccines are kept in two holes inside the ice pack.
C. Fill water up to the horizontal mark with plain tap water.
D. It can store vaccines for 24 hours. (Correct Answer)

Explanation: ### **Explanation** **1. Why Option D is the Correct Answer (The "False" Statement):** Ice packs are used within vaccine carriers and cold boxes to maintain the required temperature during transport or outreach sessions. However, a vaccine carrier (containing 4 ice packs) can maintain the cold chain for approximately **24–48 hours** (depending on the ambient temperature and frequency of opening). A **single ice pack** on its own cannot store vaccines for 24 hours; it is merely a cooling element. Furthermore, vaccines are never stored "inside" or "for" a specific duration by an ice pack alone; they are stored within the equipment the ice pack cools. **2. Analysis of Other Options:** * **Option A (True):** The ice pack is indeed considered the **smallest and most basic component** of the cold chain system. * **Option B (True):** Standard ice packs used in the Universal Immunization Programme (UIP) have two specific indentations or "holes" designed to hold two vaccine vials (typically reconstituted ones like Measles or BCG) during an immunization session to keep them cool while in use. * **Option C (True):** Ice packs should be filled with **plain tap water** up to the horizontal level/fill line. One must leave a small space at the top to allow for the expansion of water as it turns into ice, preventing the pack from bursting. **3. High-Yield Clinical Pearls for NEET-PG:** * **Conditioned Ice Packs:** To prevent freezing-sensitive vaccines (DPT, Pentavalent, TT, Hepatitis B) from coming into contact with a sub-zero surface, ice packs must be "conditioned" (kept at room temperature until ice starts to melt and water sloshes inside) before being placed in the carrier. * **Cold Chain Sequence:** Manufacturer → Primary (GMSD) → Secondary (State/Regional) → Tertiary (District) → PHC/CHC → Subcenter/Village (Vaccine Carrier). * **Ice Pack Composition:** They contain only water; no salt is added as it lowers the freezing point too much, risking damage to T-series vaccines.

Question 307: The 17D vaccine is used for the prevention and control of which disease?

A. Yellow fever (Correct Answer)
B. Japanese encephalitis
C. Hemorrhagic fever
D. Dengue

Explanation: **Explanation:** The **17D vaccine** is a live-attenuated preparation specifically used for the prevention of **Yellow Fever**. It is derived from the wild-type Asibi strain and is considered one of the most effective vaccines ever developed, providing long-lasting immunity (often lifelong) after a single subcutaneous dose. **Why the other options are incorrect:** * **Japanese Encephalitis (JE):** While JE vaccines exist, the most common strains used are the **SA 14-14-2** (live-attenuated) or the Jenvac (inactivated). 17D is specific only to the Yellow Fever virus. * **Hemorrhagic Fever:** This is a broad clinical syndrome caused by various viruses (e.g., Ebola, Lassa, Marburg). There is no single "17D" vaccine for this group; vaccines for specific hemorrhagic fevers (like Ervebo for Ebola) are distinct. * **Dengue:** The most recognized vaccine for Dengue is **Dengvaxia (CYD-TDV)**, which is a tetravalent live-attenuated vaccine. While it uses a Yellow Fever 17D backbone (chimeric technology), the 17D vaccine itself is the primary vaccine for Yellow Fever. **High-Yield Clinical Pearls for NEET-PG:** * **Route & Dose:** 0.5 ml, Subcutaneous (SC). * **Immunity:** Starts after 7–10 days. For international travel, the certificate becomes valid **10 days after vaccination** and is now valid for **life**. * **Contraindications:** Infants <6 months, pregnancy (unless high risk), and individuals with **egg allergy** (as it is grown in chick embryos) or immunocompromised states. * **Cold Chain:** It is highly heat-sensitive and must be stored between **+2°C to +8°C**.

Question 308: Regarding Schick's test, which of the following statements is false?

A. An erythematous reaction in both arms indicates a positive test.
B. A positive test means that the person is immune to diphtheria. (Correct Answer)
C. Diphtheria antitoxin is given intradermally.
D. None of the above.

Explanation: ### Explanation **1. Why the Correct Answer is Right (Option B)** The **Schick test** is used to determine the **susceptibility** of an individual to Diphtheria, not their immunity. * **Positive Test:** If the person lacks antibodies (antitoxin), the injected toxin causes local inflammation (erythema). Therefore, a **positive test means the person is susceptible** to Diphtheria. * **Negative Test:** If the person has sufficient antibodies, the toxin is neutralized, and no reaction occurs. A **negative test means the person is immune.** **2. Analysis of Other Options** * **Option A (Erythematous reaction in both arms):** This describes a **Combined Reaction**. It occurs when a person is both susceptible to the toxin (reaction in the test arm) and hypersensitive to the protein (reaction in the control arm). Since it includes a positive reaction to the toxin, it is considered a positive result. * **Option C (Diphtheria antitoxin is given intradermally):** This statement is technically **False** in the context of the standard Schick test procedure. The Schick test involves injecting **Diphtheria Toxin** (0.1 ml) into the test arm and **Inactivated Toxin (Toxoid)** into the control arm. **Antitoxin** is used for passive immunization or treatment, not as the reagent for the Schick test. However, in the context of this specific MCQ, Option B is the "most false" and classically tested conceptual error. **3. NEET-PG High-Yield Pearls** * **Reagents:** Test arm (0.1 ml Schick toxin); Control arm (0.1 ml heat-inactivated toxin). * **Reading:** Results are read at **48 hours** and again at **4–7 days**. * **Interpretation Summary:** * **Negative:** No reaction (Immune). * **Positive:** Red flush in test arm only (Susceptible). * **False-Positive:** Reaction in both arms that fades quickly (Immune but hypersensitive). * **Combined:** Reaction in both arms, but test arm reaction persists longer (Susceptible and hypersensitive). * **Current Status:** Schick test is largely obsolete and replaced by serum antitoxin titration (ELISA).

Question 309: Which of the following is NOT true about polio?

A. The Sabin vaccine is an attenuated, oral vaccine.
B. The Salk vaccine is a killed, formalized vaccine.
C. Vaccine-induced polio is usually due to Type 2 virus. (Correct Answer)
D. The most common type of poliovirus in epidemics is Type 1.

Explanation: ### Explanation **1. Why Option C is the Correct (False) Statement:** Vaccine-Associated Paralytic Poliomyelitis (VAPP) is most commonly caused by **Type 3** poliovirus, followed by Type 2. While Type 2 was the most common cause of *Vaccine-Derived Polioviruses (VDPVs)*—leading to its removal from the trivalent OPV to create the bivalent OPV—the specific clinical entity of VAPP in vaccine recipients is traditionally linked to Type 3 due to its higher rate of genetic reversion to neurovirulence. **2. Analysis of Other Options:** * **Option A (True):** The **Sabin vaccine** is the Oral Polio Vaccine (OPV). It contains live-attenuated viruses that induce both systemic (IgG) and local intestinal immunity (IgA), which is crucial for breaking the chain of transmission. * **Option B (True):** The **Salk vaccine** is the Inactivated Polio Vaccine (IPV). It is a "killed" vaccine prepared by inactivating the virus with **formaldehyde**. It provides excellent humoral immunity but minimal intestinal immunity. * **Option D (True):** Historically, **Type 1** poliovirus has been the most common cause of paralytic poliomyelitis epidemics and is the most difficult to eradicate. **3. NEET-PG High-Yield Pearls:** * **The "Switch":** India switched from tOPV (Types 1, 2, 3) to bOPV (Types 1, 3) in April 2016 to eliminate the risk of Type 2 VDPV. * **Pulse Polio Immunization (PPI):** Aimed at children <5 years; uses "National Immunization Days" (NIDs) to replace wild virus with vaccine virus in the environment. * **Last Case in India:** Reported on January 13, 2011 (Howrah, West Bengal). India was declared Polio-free by the WHO on March 27, 2014. * **Storage:** OPV is the most heat-sensitive vaccine; stored at -20°C. VVM (Vaccine Vial Monitor) is used to check potency.

Question 310: What is the mortality rate of measles in developing countries?

A. 10% (Correct Answer)
B. 20%
C. 30%
D. 40%

Explanation: **Explanation:** Measles is a highly contagious viral infection that remains a significant cause of childhood mortality globally. In developed nations, the case fatality rate (CFR) is typically low (around 0.1%). However, in **developing countries**, the mortality rate is significantly higher, reaching approximately **10%**. In cases of severe outbreaks among malnourished populations or displaced communities (e.g., refugee camps), this rate can even surge to 20-30%. **Why 10% is correct:** The high mortality in developing regions is attributed to the interplay of malnutrition (specifically Vitamin A deficiency), overcrowding, and lack of access to supportive care. Complications such as secondary bacterial pneumonia (the most common cause of death), severe diarrhea leading to dehydration, and encephalitis drive this 10% figure. **Analysis of Incorrect Options:** * **20% (Option B):** While mortality can reach this level in specific high-risk pockets or during famine conditions, it is not the standard epidemiological average for developing countries. * **30% & 40% (Options C & D):** These figures are excessively high and do not represent the general mortality statistics for measles, even in resource-limited settings. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin A Supplementation:** Administering two doses of Vitamin A (24 hours apart) is proven to reduce measles mortality by 50%. * **Most Common Complication:** Otitis media. * **Most Common Cause of Death:** Pneumonia (often secondary bacterial infection). * **SSPE (Subacute Sclerosing Panencephalitis):** A rare, delayed, fatal neurological complication occurring years after the initial infection. * **Isolation:** Respiratory isolation is required for 4 days after the onset of the rash.

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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