Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 171: Which vaccine is given at birth?

A. Oral Polio Vaccine (OPV) (Correct Answer)
B. Diphtheria, Pertussis, and Tetanus (DPT)
C. Measles
D. Measles, Mumps, and Rubella (MMR)

Explanation: ### Explanation **Correct Answer: A. Oral Polio Vaccine (OPV)** According to the **National Immunization Schedule (NIS)** in India, three vaccines are administered at birth (the "Birth Dose"): 1. **BCG** (Bacillus Calmette–Guérin) 2. **OPV-0** (Oral Polio Vaccine zero dose) 3. **Hepatitis B** (Birth dose) The **OPV-0 dose** is administered within the first 15 days of life to induce local mucosal immunity (IgA) in the gut before the infant is exposed to wild polioviruses. This is a crucial step in the polio eradication strategy. **Analysis of Incorrect Options:** * **B. DPT:** The primary series of DPT (now given as part of the **Pentavalent vaccine**) starts at **6 weeks** of age, followed by doses at 10 and 14 weeks. It is not given at birth because the neonatal immune response to these antigens is suboptimal. * **C. Measles:** In India, the first dose of the Measles-Rubella (MR) vaccine is given at **9 completed months** (9–12 months). Administering it earlier is ineffective due to the presence of interfering maternal antibodies. * **D. MMR:** This is generally administered in private practice (IAP schedule) at **9 months (as MR/MMR)** or 15 months. It is never given at birth. **High-Yield Clinical Pearls for NEET-PG:** * **OPV-0 Dose:** Must be given within **15 days** of birth. * **Hepatitis B Birth Dose:** Must be given within **24 hours** to prevent vertical transmission from mother to child. * **BCG:** Can be given up to **1 year** of age if missed at birth (though the dose changes from 0.05ml to 0.1ml after 4 weeks). * **Pentavalent Vaccine:** Includes DPT, Hep B, and Hib (Haemophilus influenzae type b). It replaced the standalone DPT in the NIS.

Question 172: A child is suffering from varicella. The child's aunt is pregnant. At what earliest point can the child safely meet her aunt?

A. When the lesions have crusted (Correct Answer)
B. Immediately
C. Anytime, as the child is the aunt's favorite
D. After the delivery of the baby

Explanation: **Explanation:** **1. Why Option A is Correct:** The infectivity of Varicella (Chickenpox) is determined by the presence of live virus in the vesicular fluid and respiratory secretions. A patient is considered infectious from **48 hours before the onset of the rash** until **all lesions have crusted (scabbed over)**. Once the lesions are crusted, the virus is no longer viable, and the child is no longer contagious. For a pregnant woman, avoiding contact until this stage is crucial because primary varicella infection during pregnancy can lead to **Congenital Varicella Syndrome** (if early in pregnancy) or severe neonatal varicella. **2. Analysis of Incorrect Options:** * **Option B:** Incorrect. Meeting immediately while the child has active vesicles would expose the aunt to a high risk of infection via respiratory droplets or direct contact with lesion fluid. * **Option C:** Incorrect. Emotional attachment does not alter the biological period of communicability. This is a "distractor" option. * **Option D:** Incorrect. While waiting until after delivery is safe, it is not the *earliest* point. The question specifically asks for the earliest safe window, which is once the child is no longer infectious (crusting stage). **3. NEET-PG High-Yield Pearls:** * **Incubation Period:** 14–16 days (Range: 10–21 days). * **Secondary Attack Rate:** Very high (>90%). * **Rash Characteristics:** Centripetal distribution, pleomorphic (all stages of rash—papule, vesicle, crust—seen simultaneously), and "dew-drop on a rose petal" appearance. * **Post-Exposure Prophylaxis:** For susceptible pregnant women exposed to varicella, **Varicella-Zoster Immunoglobulin (VZIG)** should be administered within 72–96 hours to prevent or attenuate the disease. Live attenuated vaccines are contraindicated during pregnancy.

Question 173: What is the most common cause of vaccine failure?

A. Improper storage
B. Improper administration
C. Inappropriate manufacturing
D. Maternally derived antibodies (Correct Answer)

Explanation: **Explanation:** The most common cause of vaccine failure is the presence of **maternally derived antibodies (MDAs)**. In the early months of life, IgG antibodies transferred across the placenta provide passive immunity to the infant. However, these same antibodies can neutralize live-attenuated vaccines (like Measles or BCG) before the infant’s own immune system can recognize the antigen and develop a primary immune response. This is precisely why the Measles vaccine is scheduled at 9 months—to wait for maternal antibody titers to wane sufficiently to allow for successful seroconversion. **Analysis of Incorrect Options:** * **A. Improper storage:** While a major concern in developing countries (Cold Chain failure), modern logistics and heat-sensitive indicators (VVM) have reduced this. It is a common cause of *reduced potency*, but not the most frequent cause of failure overall. * **B. Improper administration:** Errors in route (e.g., giving BCG subcutaneously instead of intradermally) can lead to local complications or poor response, but these are human errors that occur less frequently than the biological interference of MDAs. * **C. Inappropriate manufacturing:** Vaccines undergo rigorous quality control and WHO pre-qualification; manufacturing defects are extremely rare in the modern era. **High-Yield NEET-PG Pearls:** * **Primary Vaccine Failure:** Failure of the host to mount an initial immune response (often due to MDAs or host genetics). * **Secondary Vaccine Failure:** Waning of immunity over time after an initial successful response (requires booster doses). * **Cold Chain:** The most heat-sensitive vaccine is **OPV**; the most heat-resistant is **Hepatitis B**. * **Measles:** The most common cause of "Measles-like illness" in a vaccinated child is primary vaccine failure due to administration before 9 months of age.

Question 174: Which of the following is a vaccine-preventable cancer?

A. Endometrial cancer
B. Breast cancer
C. Cervical cancer (Correct Answer)
D. Ovarian cancer

Explanation: ### Explanation **Correct Answer: C. Cervical cancer** **1. Why Cervical Cancer is the Correct Answer:** Cervical cancer is primarily caused by persistent infection with high-risk strains of the **Human Papillomavirus (HPV)**, most notably types **16 and 18**. Because the primary oncogenic driver is a virus, vaccination against HPV can prevent the precursor lesions and subsequent development of the malignancy. Currently available vaccines (e.g., Quadrivalent/Gardasil, Bivalent/Cervarix, and Nonavalent) are highly effective when administered before the onset of sexual activity. **2. Why the Other Options are Incorrect:** * **A, B, and D (Endometrial, Breast, and Ovarian Cancer):** These are non-communicable malignancies driven by a complex interplay of genetics, hormonal factors (estrogen exposure), lifestyle, and environmental triggers. They are not caused by infectious agents; therefore, no preventive vaccine exists for these cancers. **3. High-Yield Clinical Pearls for NEET-PG:** * **Other Vaccine-Preventable Cancers:** Apart from Cervical cancer (HPV), **Hepatocellular Carcinoma (HCC)** is vaccine-preventable via the **Hepatitis B vaccine**. * **HPV Vaccine Schedule (IAP/WHO):** * 9–14 years: 2 doses (0, 6 months). * 15 years and older: 3 doses (0, 1–2, 6 months). * **Screening vs. Prevention:** While the vaccine provides *primary prevention*, the **Pap smear** and **VIA/VILI** (Visual Inspection with Acetic acid/Lugol’s Iodine) remain the gold standard for *secondary prevention* (early detection). * **Target Strains:** HPV 16 and 18 cause ~70% of cervical cancers; HPV 6 and 11 cause ~90% of genital warts.

Question 175: Which statement is NOT true regarding the Polio vaccine?

A. It is difficult to maintain the cold chain for the vaccine.
B. The Salk vaccine does not cause paralysis.
C. It helps in increasing immunity.
D. Immunity takes a long time to develop. (Correct Answer)

Explanation: ### Explanation **1. Why Option D is the Correct Answer (The "Not True" Statement):** Immunity against Polio develops **rapidly**, not slowly. In the case of the Oral Polio Vaccine (OPV), local intestinal immunity (IgA) is established quickly, which is crucial for breaking the chain of transmission. For the Inactivated Polio Vaccine (IPV), systemic immunity (IgG) develops shortly after the primary series. In outbreak scenarios, OPV is used specifically because it induces fast, large-scale "herd effect" through secondary spread. **2. Analysis of Incorrect Options:** * **Option A (Difficult to maintain cold chain):** This is **true**. OPV is the most heat-sensitive vaccine in the Universal Immunization Programme (UIP). It must be stored at -20°C (deep freezer) at the district level and 2-8°C at the PHC level. The use of the Vaccine Vial Monitor (VVM) is mandatory to check its potency. * **Option B (Salk vaccine does not cause paralysis):** This is **true**. The Salk vaccine (IPV) contains killed viruses; therefore, it cannot revert to neurovirulence. In contrast, the Sabin vaccine (OPV) carries a rare risk of Vaccine-Associated Paralytic Poliomyelitis (VAPP). * **Option C (Helps in increasing immunity):** This is **true**. Both OPV and IPV are highly effective. OPV provides both humoral (IgG) and intestinal (IgA) immunity, while IPV provides robust systemic humoral immunity. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vaccine of Choice:** India currently uses **bOPV** (Type 1 and 3) and **fractional IPV (fIPV)**. * **fIPV Route/Dose:** 0.1 ml, Intradermal (ID) at the right upper arm at 6, 14 weeks, and 9 months. * **VVM:** OPV is the only vaccine where the VVM is placed on the **cap** (until recently) or the label; it is the gold standard for heat sensitivity. * **Herd Immunity:** OPV provides herd immunity through "contact immunization" (fecal-oral spread of the vaccine virus), whereas IPV does not.

Question 176: In Uveitis, blindness can be prevented by the administration of?

A. Measles vaccines (Correct Answer)
B. Rubella vaccines
C. BCG vaccines
D. Diphtheria vaccines

Explanation: **Explanation:** The correct answer is **Measles vaccine**. **Why Measles Vaccine is Correct:** Measles is a leading cause of childhood blindness in developing countries. The virus causes severe ocular complications, including **keratitis** and **uveitis**, which can lead to corneal scarring and ulceration. Furthermore, Measles infection significantly depletes **Vitamin A** stores in the body. Vitamin A is essential for maintaining the integrity of the corneal epithelium; its deficiency (Xerophthalmia) combined with measles-induced inflammation leads to rapid corneal melting (**keratomalacia**) and permanent blindness. Therefore, the Measles vaccine acts as a primary preventive measure against these blinding complications. **Why Other Options are Incorrect:** * **Rubella Vaccine:** While Congenital Rubella Syndrome (CRS) causes cataracts and glaucoma, the vaccine is primarily aimed at preventing congenital malformations rather than treating or preventing blindness via the uveitis pathway in general populations. * **BCG Vaccine:** Used for Tuberculosis prevention. While ocular TB exists, BCG is not a standard public health intervention specifically targeted at preventing blindness. * **Diphtheria Vaccine:** Diphtheria primarily affects the upper respiratory tract or skin (via exotoxins) and does not have a direct causal link to uveitis or nutritional blindness. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin A Supplementation:** Always administered alongside the Measles vaccine (1 lakh IU at 9 months, 2 lakh IU at 16-24 months) to prevent complications. * **Most common cause of blindness in children (Global):** Vitamin A deficiency (often triggered by Measles). * **Koplik Spots:** Pathognomonic pre-eruptive sign of Measles found on the buccal mucosa. * **MC Cause of Death in Measles:** Bronchopneumonia.

Question 177: What is the recommended route of administration for the DPT vaccine?

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

Explanation: **Explanation:** The **DPT vaccine** (Diphtheria, Pertussis, and Tetanus) is an adsorbed vaccine containing aluminum salts as adjuvants. The correct route of administration is **Intramuscular (IM)**, typically administered in the anterolateral aspect of the mid-thigh in infants. **1. Why Intramuscular (IM) is correct:** Adsorbed vaccines must be injected deep into the muscle. The muscle tissue has high vascularity, which allows for optimal processing of the antigen. More importantly, the IM route ensures the adjuvant remains deep within the tissue to trigger a slow, sustained immune response. **2. Why other options are incorrect:** * **Subcutaneous (SC):** If DPT is given subcutaneously, the aluminum adjuvant causes severe local irritation, leading to sterile abscesses, granulomas, or tissue necrosis. * **Oral:** This route is reserved for live attenuated vaccines that mimic natural infection through the gut mucosa (e.g., OPV, Rotavirus). DPT antigens would be degraded by gastric acid. * **Intravenous (IV):** Vaccines are never given IV as this could lead to immediate systemic toxicity or anaphylaxis without providing the necessary "depot" effect for immunity. **High-Yield NEET-PG Pearls:** * **Site:** Anterolateral thigh (Vastus lateralis) is preferred over the gluteal region in infants to avoid sciatic nerve injury and because the gluteal fat pad may interfere with absorption. * **Storage:** DPT is **heat-stable but freeze-sensitive**. It must be stored at +2°C to +8°C. If frozen, the "Shake Test" is used to check for vaccine damage. * **Contraindication:** A history of encephalopathy within 7 days of a previous dose is a contraindication for the Pertussis component.

Question 178: After administering a live vaccine, at what minimum interval should immunoglobulins be given?

A. 1 week
B. 2 weeks (Correct Answer)
C. 10 weeks
D. 12 weeks

Explanation: ### Explanation The core principle behind the timing of vaccines and immunoglobulins (IG) is the **interference of passive antibodies with the immune response to live vaccines.** **1. Why 2 weeks is the correct answer:** When a live attenuated vaccine (e.g., MMR, Varicella) is administered, the virus must replicate within the body to stimulate an active immune response. If immunoglobulins are given too soon after the vaccine, the pre-formed antibodies will neutralize the vaccine virus before it can replicate, leading to vaccine failure. A **minimum interval of 2 weeks** is required to allow the body to initiate its own immune response before the exogenous antibodies are introduced. **2. Analysis of Incorrect Options:** * **1 week (Option A):** This is too short; the vaccine virus is still in the active replication phase, and IG administration would likely neutralize it. * **10 weeks and 12 weeks (Options C & D):** These intervals are unnecessarily long for this specific sequence (Vaccine $\rightarrow$ IG). However, note that if the sequence is reversed (**IG $\rightarrow$ Vaccine**), a longer gap of **3 to 11 months** (depending on the dose and type of IG) is required to ensure the passive antibodies have waned sufficiently. **3. High-Yield Clinical Pearls for NEET-PG:** * **Live Vaccine $\rightarrow$ IG:** Wait **2 weeks**. * **IG $\rightarrow$ Live Vaccine:** Wait **3–11 months** (Standard is often cited as 12 weeks/3 months for low-dose IG, but varies by product). * **Exceptions:** The **Yellow Fever** and **Oral Polio (OPV)** vaccines are generally not affected by IG. * **Simultaneous Administration:** If post-exposure prophylaxis is needed (e.g., Rabies or Hepatitis B), the vaccine and IG must be given at **different anatomical sites**. * **Inactivated Vaccines:** These are not affected by IG; they can be given simultaneously or at any interval.

Question 179: Which of the following is NOT a contraindication to DPT vaccination?

A. Severe local reaction to a previous DPT dose (Correct Answer)
B. High fever following a previous DPT dose
C. Infantile spasms
D. Seizures following a previous DPT dose

Explanation: **Explanation:** The core concept in DPT (Diphtheria, Pertussis, and Tetanus) vaccination is identifying absolute contraindications versus precautions. The **Pertussis component** is the most reactogenic and is responsible for most neurological adverse events. **Why Option A is the correct answer:** A **severe local reaction** (such as extensive redness or swelling) is considered a **minor side effect** or a precaution, but it is **NOT** a contraindication to subsequent doses. While it may be uncomfortable, it does not pose a life-threatening risk or indicate a permanent neurological predisposition. **Analysis of Incorrect Options (Contraindications):** * **B. High fever (>40.5°C/105°F):** Fever of this magnitude within 48 hours of a previous dose is a contraindication/precaution because it may trigger febrile seizures or indicate extreme sensitivity. * **C. Infantile spasms:** Any progressive or unstable neurological disorder (like uncontrolled epilepsy or infantile spasms) is a strict contraindication to the Pertussis component until the condition is stabilized. * **D. Seizures:** Seizures occurring within 3 days of a previous dose are a contraindication to further Pertussis vaccination due to the risk of encephalopathy. **NEET-PG High-Yield Pearls:** 1. **Absolute Contraindications to DPT:** Anaphylaxis to vaccine components and **Encephalopathy** (e.g., coma, prolonged seizures) within 7 days of a previous dose. 2. **False Contraindications:** Mild respiratory infections, low-grade fever, malnutrition, and family history of seizures are **NOT** contraindications. 3. **Alternative:** If Pertussis is contraindicated, the child should be given the **DT (Diphtheria and Tetanus)** vaccine instead. 4. **Acellular Pertussis (aP):** This version has fewer side effects than the whole-cell (wP) version used in the National Immunization Schedule.

Question 180: Which of the following is NOT a type of vaccine-derived poliovirus?

A. cVDPV
B. iVDPV
C. mVDPV (Correct Answer)
D. aVDPV

Explanation: **Explanation:** Vaccine-derived polioviruses (VDPVs) are rare strains of poliovirus that have genetically mutated from the attenuated virus contained in the Oral Polio Vaccine (OPV). According to the WHO, VDPVs are classified into three specific categories based on their origin and transmission characteristics. **Why Option C (mVDPV) is the correct answer:** There is no such classification as **mVDPV**. While "m" often stands for "monovalent" in vaccinology (e.g., mOPV), it is not a recognized category of vaccine-derived poliovirus. This makes it the "except" or "NOT" type in the list. **Analysis of Incorrect Options:** * **A. cVDPV (Circulating VDPV):** These occur in communities with low immunization coverage where the attenuated virus from OPV circulates for a long period (usually >12 months), regaining neurovirulence and causing outbreaks. * **B. iVDPV (Immunodeficiency-associated VDPV):** These are isolated from individuals with rare primary immunodeficiencies (e.g., B-cell deficiency) who cannot clear the intestinal infection and excrete the virus for prolonged periods. * **D. aVDPV (Ambiguous VDPV):** These are isolates that do not fit into the other two categories (e.g., isolates from sewage with no known source or isolates from healthy individuals with no known immunodeficiency). **High-Yield Clinical Pearls for NEET-PG:** * **Genetic Mutation:** A virus is classified as VDPV if it is >1% divergent from the parent OPV strain for Type 1 and 3, or >0.6% for Type 2. * **The Switch:** To prevent cVDPV2 outbreaks, India and the world switched from **tOPV** (trivalent) to **bOPV** (bivalent, containing only types 1 and 3) in April 2016. * **Most Common Type:** Historically, **Type 2** (VDPV2) has been responsible for over 90% of cVDPV cases globally.

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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