Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 71: In which scenario is pneumococcal vaccine most effective?

A. When given preoperatively (Correct Answer)
B. When given postoperatively
C. Against all strains of pneumococcus
D. Against Gram-negative bacteria

Explanation: **Explanation:** **Why Option A is correct:** The pneumococcal vaccine (typically PPSV23 or PCV13/20) is most effective when administered **preoperatively**, specifically in patients scheduled for elective **splenectomy**. The spleen plays a critical role in filtering encapsulated bacteria (like *S. pneumoniae*) and producing opsonizing antibodies. To ensure an optimal immune response, the vaccine should be given at least **2 weeks before surgery**. This allows the body to mount a robust antibody titer while the splenic tissue is still functional, providing maximum protection against Post-Splenectomy Sepsis. **Analysis of Incorrect Options:** * **Option B:** While the vaccine can be given postoperatively if the preoperative window is missed, the immune response is often suboptimal and delayed, leaving the patient vulnerable during the immediate recovery phase. * **Option C:** No pneumococcal vaccine covers all strains. PPSV23 covers the 23 most common virulent serotypes, but there are over 90 known serotypes of *Streptococcus pneumoniae*. * **Option D:** *Streptococcus pneumoniae* is a **Gram-positive** coccus. The vaccine has no efficacy against Gram-negative organisms (like *E. coli* or *Pseudomonas*). **High-Yield Clinical Pearls for NEET-PG:** * **The "Big Three" Vaccines for Splenectomy:** Patients must be immunized against **Pneumococcus, Haemophilus influenzae type b (Hib), and Meningococcus**. * **Timing:** If elective, vaccinate ≥2 weeks before; if emergency splenectomy, vaccinate 2 weeks after surgery (to avoid the "stunning" effect on the immune system post-trauma). * **Target Population:** Apart from splenectomy, it is indicated for the elderly (>65 years), those with chronic heart/lung disease, and immunocompromised states (HIV, Nephrotic syndrome). * **Revaccination:** A one-time booster is usually recommended after 5 years for high-risk individuals.

Question 72: Which vaccine can cause adverse effects in persons with an allergy to eggs?

A. Measles
B. Rubella
C. Rabies (Correct Answer)
D. Mumps

Explanation: ### Explanation The correct answer is **Rabies (Option C)**. **1. Why Rabies is the correct answer:** The potential for allergic reactions to vaccines in egg-allergic individuals depends on the substrate used for viral cultivation. Certain Rabies vaccines, specifically **Purified Chick Embryo Cell (PCEC) vaccines**, are cultured in primary cultures of chicken embryonic fibroblasts. These vaccines may contain trace amounts of egg protein (ovalbumin), which can trigger hypersensitivity reactions or anaphylaxis in sensitized individuals. While modern cell-culture vaccines are generally safe, PCEC remains the primary concern in this context. **2. Why the other options are incorrect:** * **Measles, Mumps, and Rubella (MMR):** Although these viruses are grown in chick embryo fibroblast cultures, the World Health Organization (WHO) and the Advisory Committee on Immunization Practices (ACIP) state that the amount of egg protein is negligible. Large-scale studies have shown that MMR vaccines can be safely administered to children with severe egg allergies without prior skin testing. * **Note:** In contrast, **Yellow Fever** and **Influenza** vaccines are grown in embryonated chicken eggs and contain much higher concentrations of egg protein, making them strictly contraindicated or requiring caution in egg-allergic patients. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vaccines to avoid/caution in Egg Allergy:** Yellow Fever (highest risk), Influenza (Inactivated and Live), and Rabies (PCEC type). * **Safe for Egg Allergy:** MMR, MMRV, and most recombinant vaccines. * **Substrate Check:** If a question asks for the "most" contraindicated vaccine in egg allergy and Yellow Fever is an option, it is usually the primary answer. In this specific set, Rabies (PCEC) is the relevant clinical concern. * **Gelatin Allergy:** Interestingly, many reactions attributed to "egg allergy" in MMR vaccines are actually due to **gelatin** used as a stabilizer.

Question 73: Which of the following is NOT a true statement regarding the Haemophilus influenzae type b (Hib) vaccine?

A. It protects against non-encapsulated strains of Haemophilus influenzae. (Correct Answer)
B. Catch-up vaccination is recommended before the age of 5 years.
C. It can be administered to infants less than 6 months of age.
D. It should be given at least 2 weeks prior to splenectomy.

Explanation: ### Explanation **1. Why Option A is the correct answer (The "False" statement):** The Hib vaccine is a **conjugate vaccine** specifically designed to target the **polyribosylribitol phosphate (PRP)** capsule of *Haemophilus influenzae* type b. Because it targets this specific capsular polysaccharide, it provides no protection against **non-encapsulated (non-typeable) strains**, which commonly cause mucosal infections like otitis media, sinusitis, and bronchitis. It only protects against the invasive "type b" encapsulated strain responsible for meningitis and epiglottitis. **2. Analysis of Incorrect Options (True statements):** * **Option B:** In healthy children, the risk of Hib disease decreases significantly after age 5. Therefore, catch-up vaccination is generally **not recommended for children aged 5 years or older** unless they have underlying high-risk conditions (e.g., asplenia or HIV). * **Option C:** Under the National Immunization Schedule (NIS) and IAP guidelines, the Hib vaccine (often as part of the **Pentavalent vaccine**) is administered at **6, 10, and 14 weeks** of age. Thus, it is routinely given to infants under 6 months. * **Option D:** Patients undergoing splenectomy are at high risk for **Overwhelming Post-Splenectomy Infection (OPSI)** caused by encapsulated bacteria (*S. pneumoniae, H. influenzae, N. meningitidis*). Ideally, vaccines should be administered at least **2 weeks before** an elective splenectomy to allow for an adequate immune response. **3. High-Yield Clinical Pearls for NEET-PG:** * **Type of Vaccine:** Conjugate vaccine (T-cell dependent response), which allows for immunogenicity in infants <2 years. * **Pentavalent Vaccine:** Includes DPT, Hep B, and Hib. * **Most Common Presentation:** Before the vaccine, Hib was the leading cause of **bacterial meningitis** in children aged 2 months to 5 years. * **Storage:** Should be stored at **+2°C to +8°C** (Never freeze).

Question 74: What is the recommended age for the first dose of vitamin A supplementation?

A. 3 months
B. 6 months
C. 9 months (Correct Answer)
D. 12 months

Explanation: ### Explanation **Correct Answer: C. 9 months** **Why 9 months is correct:** Under the **National Prophylaxis Programme against Nutritional Blindness** and the **Universal Immunization Programme (UIP)** in India, the first dose of Vitamin A (1 lakh IU) is administered at **9 completed months**. This timing is strategically synchronized with the **first dose of the Measles/MRIs vaccine**. Measles infection significantly depletes Vitamin A stores and is a leading cause of childhood blindness; therefore, co-administration provides essential immune support and ocular protection during this vulnerable period. **Why other options are incorrect:** * **3 months & 6 months:** Infants are generally protected by maternal antibodies and Vitamin A stores from breast milk during the first six months. Routine supplementation is not recommended this early unless the infant is non-breastfed or showing clinical signs of deficiency. * **12 months:** Waiting until 12 months would leave the infant unprotected during the high-risk window (9–12 months) when complementary feeding begins and maternal antibody levels for measles decline. **High-Yield Clinical Pearls for NEET-PG:** * **Dosage Schedule:** * **1st Dose:** 1 lakh IU (1 ml) at 9 months. * **2nd to 9th Dose:** 2 lakh IU (2 ml) every 6 months until the age of 5 years. * **Total Doses:** A child receives a total of **9 doses**. * **Total Cumulative Dose:** **17 lakh IU** (1 + [8 × 2] = 17). * **Oil-based solution:** Vitamin A is fat-soluble and is administered orally using a calibrated spoon. * **Therapeutic Dose:** For active Xerophthalmia, the schedule is Day 0, Day 1, and Day 14 (Age-specific dosing: <6m: 50k IU; 6-12m: 1 lakh IU; >12m: 2 lakh IU).

Question 75: Which of the following statements regarding vaccine reconstitution is FALSE?

A. Yellow fever vaccine is reconstituted with cold physiological saline.
B. JE vaccine is reconstituted with sterile water. (Correct Answer)
C. Measles vaccine is reconstituted with distilled water.
D. BCG vaccine is reconstituted with normal saline.

Explanation: ### Explanation The key to answering this question lies in knowing the specific diluents required for lyophilized (freeze-dried) vaccines to maintain their potency and prevent adverse reactions. **1. Why Option B is the Correct (False) Statement:** The **Japanese Encephalitis (JE) vaccine** (specifically the live attenuated SA 14-14-2 strain used in the Universal Immunization Programme) is reconstituted with **Phosphate Buffered Saline (PBS)**, not sterile water. Using the wrong diluent can alter the pH, leading to vaccine instability or increased local irritation at the injection site. **2. Analysis of Other Options:** * **Option A (Yellow Fever):** This is **True**. Yellow fever vaccine is reconstituted with **cold physiological saline (0.9% NaCl)**. It is highly heat-sensitive and must be used within 30 minutes of reconstitution. * **Option C (Measles/MR):** This is **True**. Measles, Mumps, and Rubella (MMR) or MR vaccines are reconstituted with **Sterile Water for Injection**. * **Option D (BCG):** This is **True**. BCG is reconstituted with **Normal Saline**. Using sterile water instead of saline for BCG can cause endosmosis, leading to the swelling and bursting of the live bacilli, rendering the vaccine ineffective. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "4-Hour Rule":** Most reconstituted vaccines (BCG, Measles, JE) must be discarded after **4 hours** (or at the end of the session, whichever is earlier). Yellow Fever is the exception (discard after 30 mins). * **Temperature:** Diluents should ideally be stored at the same temperature as the vaccine (+2°C to +8°C) for at least 24 hours before use to avoid thermal shock to the organisms. * **Never Freeze Diluents:** While vaccines may be sensitive to heat, diluents should never be frozen as the glass ampoules may crack. * **Summary Table:** * **BCG:** Normal Saline * **Measles/MR:** Sterile Water * **JE:** Phosphate Buffered Saline * **Yellow Fever:** Cold Normal Saline

Question 76: Smallpox eradication was successful due to all factors except:

A. Subclinical cases do not transmit the disease
B. A highly effective vaccine was available
C. The vaccine conferred lifelong immunity
D. Cross-resistance with animal pox viruses existed (Correct Answer)

Explanation: Smallpox remains the only human infectious disease to be globally eradicated (declared by the WHO on May 8, 1980). Its eradication was possible due to specific epidemiological features of the Variola virus. ### **Explanation of the Correct Answer** **Option D** is the correct answer because it is a **false statement**. While the Smallpox vaccine was derived from the Vaccinia virus (a related orthopoxvirus), there was **no natural cross-resistance** from animal pox viruses that protected the human population. In fact, the lack of an animal reservoir was a primary reason for eradication success; the virus lived only in humans, meaning once human transmission was broken, the virus had nowhere to hide. ### **Analysis of Incorrect Options (Reasons for Eradication Success)** * **Option A:** Subclinical (asymptomatic) cases were virtually non-existent. Every infected person showed a characteristic rash, making cases easy to identify and isolate. Since subclinical cases did not transmit the disease, "surveillance-containment" was highly effective. * **Option B:** The bifurcated needle and the heat-stable freeze-dried vaccine allowed for easy administration and potency in tropical climates without a strict cold chain. * **Option C:** The vaccine provided long-lasting immunity, and a visible vaccination scar allowed health workers to easily identify immune individuals in a community. ### **NEET-PG High-Yield Pearls** * **Last Case (World):** Ali Maow Maalin in Somalia (1977) - *Variola minor*. * **Last Case (India):** Saiban Bibi in West Bengal (May 1975) - *Variola major*. * **India declared Smallpox Free:** April 1977. * **Strategy used:** Initially "Mass Vaccination," later shifted to **"Surveillance and Containment"** (Ring Vaccination), which led to final eradication. * **Incubation Period:** 10–14 days; patients are infectious from the onset of rash until the last scab falls off.

Question 77: Which of the following vaccines can be administered to a patient with known anaphylactic reactions to eggs?

A. Haemophilus influenzae type B vaccine (Correct Answer)
B. Influenza vaccine
C. Measles vaccine
D. Mumps vaccine

Explanation: ### Explanation The core concept behind this question is the manufacturing process of vaccines. Certain vaccines are cultured in **embryonated chicken eggs** or **chick embryo fibroblast cells**, which may result in trace amounts of egg protein (ovalbumin) in the final product. **1. Why Option A is Correct:** The **Haemophilus influenzae type B (HiB) vaccine** is a conjugate vaccine produced using synthetic or bacterial fermentation methods. It does not involve any egg-based medium during production. Therefore, it is completely safe for individuals with egg allergies or anaphylaxis. **2. Why the Other Options are Incorrect:** * **Influenza Vaccine (Option B):** Most inactivated and live-attenuated influenza vaccines are grown in embryonated chicken eggs. While modern guidelines suggest some may be given under supervision, they are traditionally contraindicated or require extreme caution in cases of severe anaphylaxis. * **Measles and Mumps Vaccines (Options C & D):** Both the Measles and Mumps components of the MMR vaccine are grown in **chick embryo fibroblast cultures**. Although the risk of a reaction is extremely low (as the protein is highly purified), they are historically associated with egg-related precautions in medical entrance exams compared to purely synthetic/bacterial vaccines like HiB. **3. NEET-PG High-Yield Pearls:** * **Yellow Fever Vaccine:** This contains the highest amount of egg protein and is **strictly contraindicated** in patients with egg anaphylaxis. * **Rabies (PCECV):** Purified Chick Embryo Cell Vaccine should be avoided; use Human Diploid Cell Vaccine (HDCV) instead. * **Safe Vaccines:** Oral Polio (OPV), Injectable Polio (IPV), DPT, Hepatitis B, and HiB are all egg-free and safe. * **Egg-based vaccines mnemonic:** "**M**y **M**amma **I**s **Y**ellow" (**M**easles, **M**umps, **I**nfluenza, **Y**ellow Fever).

Question 78: According to the latest guidelines of vaccination, which of the following is applicable at the age of 5 years?

A. DT Booster + Vitamin A
B. DT
C. DPT + OPV
D. DPT booster + Vitamin A (Correct Answer)

Explanation: ### Explanation The correct answer is **D (DPT booster + Vitamin A)**. This is based on the National Immunization Schedule (NIS) followed in India. **1. Why Option D is Correct:** According to the NIS, children should receive the **second booster dose of DPT** (Diphtheria, Pertussis, and Tetanus) between **5–6 years** of age. This dose is crucial to maintain immunity against these three diseases as the protection from the first booster (given at 16–24 months) begins to wane. Additionally, the **9th (and final) dose of Vitamin A** (2 lakh IU) is administered at 5 years of age. Vitamin A supplementation is given every 6 months starting from 9 months until the child reaches 5 years. **2. Why Other Options are Incorrect:** * **Option A & B (DT):** DT (Diphtheria and Tetanus) is only used if there is a specific contraindication to the Pertussis component (e.g., history of seizures or encephalopathy). In the routine schedule, DPT is the standard. * **Option C (DPT + OPV):** While DPT is correct, the **OPV booster** is administered at **16–24 months** (along with the first DPT booster and Measles-Rubella 2nd dose), not at 5 years. **3. High-Yield Facts for NEET-PG:** * **DPT vs. Td:** At 10 and 16 years, the DPT vaccine is replaced by the **Td (Tetanus and adult Diphtheria)** vaccine. The "d" is lowercase to signify a reduced dose of diphtheria toxoid. * **Vitamin A Schedule:** 1st dose at 9 months (1 lakh IU); 2nd to 9th doses every 6 months (2 lakh IU each). Total cumulative dose = **17 lakh IU**. * **Injection Site:** DPT at 5 years is typically administered in the **upper arm (Deltoid)**, unlike the primary series which is given in the anterolateral mid-thigh.

Question 79: Which vaccine must be stored in the freezer compartment of a refrigerator?

A. BCG
B. OPV (Correct Answer)
C. Measles
D. Smallpox

Explanation: **Explanation:** The correct answer is **OPV (Oral Polio Vaccine)**. In the context of the cold chain, vaccines are categorized based on their heat sensitivity. **OPV is the most heat-sensitive vaccine** in the Universal Immunization Programme (UIP). To maintain its potency, it must be stored at sub-zero temperatures (typically **-20°C**) in the freezer compartment of a refrigerator or in a Deep Freezer at the district level. **Analysis of Options:** * **OPV (Correct):** Due to its extreme thermolability, it is the only vaccine routinely kept in the freezer at the PHC level to prevent degradation. * **BCG:** This is a live attenuated vaccine, but in its **freeze-dried (lyophilized)** form, it is relatively stable at room temperature. However, under the UIP, it is stored in the refrigerator (2°C to 8°C), not the freezer. Once reconstituted, it becomes highly heat-sensitive and must be used within 4 hours. * **Measles:** Like BCG, Measles is a lyophilized vaccine stored at 2°C to 8°C. While it can be frozen without damage, it is not a *requirement* for storage at the peripheral level. * **Smallpox:** This vaccine is no longer part of routine immunization as the disease was declared eradicated in 1980. **High-Yield Clinical Pearls for NEET-PG:** * **Most Heat-Sensitive:** OPV > Measles > BCG. * **Most Heat-Resistant:** TT (Tetanus Toxoid) > Hepatitis B > DPT. * **Freeze-Sensitive Vaccines:** Never freeze T-series vaccines (TT, DPT, Pentavalent) or Hepatitis B, as freezing destroys their potency (the "Shake Test" is used to check for damage). * **VVM (Vaccine Vial Monitor):** Primarily used to monitor heat exposure; it is most critical for OPV.

Question 80: Which of the following is NOT a guideline for immunization against infectious diseases?

A. Live vaccines are contraindicated in pregnant women.
B. Live vaccines should not be administered within 3 months of giving human immunoglobulin.
C. Inactivated vaccines should not be given if there has been a significant reaction to a previous dose.
D. Hay fever, sickle cell anemia, and tuberculosis are contraindications for vaccination. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D** because hay fever, sickle cell anemia, and tuberculosis are **false contraindications** for vaccination. In clinical practice, minor allergic conditions (like hay fever), chronic diseases (like sickle cell anemia), and stable infections (like tuberculosis) do not preclude a patient from receiving vaccines. In fact, patients with sickle cell anemia are at high risk for encapsulated bacterial infections and are prioritized for vaccines like Pneumococcal and Meningococcal. **Analysis of Options:** * **Option A (Incorrect):** This is a standard guideline. Live vaccines (e.g., MMR, Varicella, Yellow Fever) are generally contraindicated in pregnancy due to the theoretical risk of the vaccine virus crossing the placenta and affecting the fetus. * **Option B (Incorrect):** This is a valid guideline. Passively acquired antibodies (Immunoglobulins) can interfere with the immune response to live vaccines (especially MMR and Varicella). A gap of at least 3–11 months (depending on the dose) is usually required. * **Option C (Incorrect):** This is a standard safety guideline. An anaphylactic or severe systemic reaction to a previous dose of any vaccine (inactivated or live) is a definitive contraindication for subsequent doses of that specific vaccine. **High-Yield NEET-PG Pearls:** * **Absolute Contraindications:** Anaphylaxis to vaccine components (e.g., neomycin, egg protein) and severe immunodeficiency (for live vaccines). * **False Contraindications:** Minor respiratory infections/diarrhea with low-grade fever, prematurity, breastfeeding, and family history of adverse events. * **The "Rule of 4 Weeks":** If two live parenteral vaccines are not administered simultaneously, they should be separated by a minimum interval of 4 weeks.

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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