Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 281: Which one of the following is a conjugated vaccine?

A. Hepatitis B
B. Rubella
C. Haemophilus influenzae type b (Correct Answer)
D. Pertussis

Explanation: ### Explanation **Correct Answer: C. Haemophilus influenzae type b (Hib)** **Why Hib is the Correct Answer:** The **Haemophilus influenzae type b (Hib)** vaccine is a **conjugated vaccine**. In its natural state, the Hib capsule is composed of a polysaccharide (Polyribosylribitol Phosphate - PRP). Polysaccharides are T-cell independent antigens, which are poorly immunogenic in children under 2 years of age. To overcome this, the polysaccharide is chemically linked (conjugated) to a carrier protein (e.g., Tetanus toxoid or Diphtheria CRM197). This conversion triggers a **T-cell dependent immune response**, leading to better immunogenicity, long-term mucosal immunity, and immunological memory in infants. **Analysis of Incorrect Options:** * **A. Hepatitis B:** This is a **Recombinant (Subunit) vaccine**. It is produced by inserting the HBsAg gene into yeast cells (*Saccharomyces cerevisiae*). * **B. Rubella:** This is a **Live Attenuated vaccine** (specifically the RA 27/3 strain). * **C. Pertussis:** The traditional vaccine is a **Killed (Whole-cell) vaccine**, while the newer acellular version (aP) is a **Subunit vaccine** containing purified components like pertussis toxoid and filamentous hemagglutinin. **NEET-PG High-Yield Pearls:** 1. **Common Conjugated Vaccines:** Remember the mnemonic **"SNH"** — *Streptococcus pneumoniae* (PCV), *Neisseria meningitidis* (MCV), and *Haemophilus influenzae* type b (Hib). Some Typhoid vaccines (TCV) are also conjugated. 2. **Advantage:** Conjugation induces **IgG production** (instead of just IgM) and provides **herd immunity** by reducing nasopharyngeal carriage. 3. **Hib Schedule:** Under the National Immunization Schedule (NIS) in India, it is administered as part of the **Pentavalent Vaccine** at 6, 10, and 14 weeks.

Question 282: All of the following vaccines can prevent pneumonia, except?

A. Measles
B. Rubella (Correct Answer)
C. Pneumococcal
D. H. influenzae

Explanation: **Explanation:** The correct answer is **Rubella**. To answer this question, one must distinguish between vaccines that target primary respiratory pathogens and those that prevent systemic infections where pneumonia is a common secondary complication. 1. **Why Rubella is the correct answer:** Rubella (German Measles) typically presents as a mild febrile rash illness with lymphadenopathy. While it can cause serious complications like encephalitis or Congenital Rubella Syndrome (CRS), it is **not** a recognized cause of pneumonia. Therefore, the Rubella vaccine does not play a role in preventing pneumonia. 2. **Why the other options are incorrect:** * **Measles:** Pneumonia is the most common cause of death associated with Measles in children. By preventing the primary infection, the Measles vaccine significantly reduces the incidence of secondary bacterial and giant-cell (Hecht's) pneumonia. * **Pneumococcal:** This vaccine targets *Streptococcus pneumoniae*, the most common bacterial cause of community-acquired pneumonia (CAP) globally. * **H. influenzae (Hib):** *Haemophilus influenzae* type b is a major cause of bacterial pneumonia and meningitis in children under five. The Hib vaccine is a core component of the Pentavalent vaccine used to reduce pneumonia mortality. **High-Yield Clinical Pearls for NEET-PG:** * **WHO Fact:** Pneumonia is the single largest infectious cause of death in children worldwide. * **Vaccines preventing Pneumonia:** Apart from the options above, the **Influenza**, **Pertussis** (Whooping cough), and **Varicella** vaccines also help prevent pneumonia. * **Measles Complication:** The most common cause of death in Measles is Pneumonia, but the most common complication overall is Otitis Media. * **Vitamin A:** Supplementation during Measles is crucial as it reduces the severity of respiratory complications and mortality.

Question 283: Who is credited with inventing the smallpox vaccine?

A. Louis Pasteur
B. Edward Jenner (Correct Answer)
C. Paul Eugene
D. John Snow

Explanation: **Explanation:** **Correct Answer: B. Edward Jenner** Edward Jenner is famously known as the "Father of Immunology." In **1796**, he observed that milkmaids who had contracted cowpox (a milder disease) appeared immune to smallpox. He conducted a landmark experiment by inoculating 8-year-old James Phipps with material from a cowpox lesion. When later exposed to smallpox, the boy did not develop the disease. This led to the development of the smallpox vaccine, the first successful vaccine in history. The term "vaccine" itself is derived from the Latin word *vacca*, meaning cow. **Why other options are incorrect:** * **A. Louis Pasteur:** Known for the "Germ Theory of Disease." He developed vaccines against **Rabies** and **Anthrax** and invented the process of pasteurization. * **C. Paul Eugene:** Likely a distractor. (Note: Paul Ehrlich is the famous figure associated with chemotherapy and the "magic bullet" concept). * **D. John Snow:** Known as the "Father of Modern Epidemiology." He is famous for tracing the source of a **Cholera** outbreak in London to the Broad Street pump. **High-Yield Facts for NEET-PG:** * **Smallpox Eradication:** Smallpox is the only human infectious disease to be completely eradicated. * **Last Case (Natural):** Occurred in Somalia in **1977** (Ali Maow Maalin). * **Global Eradication Declaration:** Declared by the WHO on **May 8, 1980**. * **Last Case in India:** Reported in **1975** (Bihar). India was declared smallpox-free in 1977. * **Bifurcated Needle:** The specific tool used for the "multiple puncture" vaccination technique for smallpox.

Question 284: Whole cell pertussis vaccine used to prevent infection can protect against which of the following?

A. Bordetella parapertussis only
B. Mild forms of Bordetella pertussis only
C. Both Bordetella pertussis and Bordetella parapertussis (Correct Answer)
D. Only against severe Pertussis

Explanation: ### Explanation **Correct Answer: C. Both *Bordetella pertussis* and *Bordetella parapertussis*** The **Whole-cell Pertussis (wP)** vaccine is derived from inactivated cultures of *Bordetella pertussis*. While its primary target is *B. pertussis* (the causative agent of classic whooping cough), it provides significant **cross-protection** against *Bordetella parapertussis*. This is because the whole-cell preparation contains a broad array of surface antigens, some of which are shared between the two species. Studies have shown that while the vaccine is more effective against *B. pertussis*, it significantly reduces the clinical severity and incidence of infections caused by *B. parapertussis*. **Analysis of Incorrect Options:** * **Option A:** Incorrect. The vaccine is specifically designed for *B. pertussis*; the protection against *B. parapertussis* is a secondary benefit due to antigenic similarity. * **Option B & D:** Incorrect. The wP vaccine is highly effective (approx. 80-90%) in preventing both mild and severe clinical manifestations of the disease, not just one specific form. **NEET-PG High-Yield Pearls:** * **wP vs. aP:** The Whole-cell vaccine (wP) generally provides better cross-protection against *B. parapertussis* than the Acellular vaccine (aP), as the latter contains only specific purified antigens (like PT, FHA) which may not be present in *B. parapertussis*. * **Adverse Effects:** wP is more reactogenic than aP, commonly causing fever and local reactions. A rare but serious contraindication is **progressive neurological disorders** (e.g., uncontrolled epilepsy). * **Vaccine Type:** It is a **killed/inactivated** bacterial vaccine. * **Schedule:** Administered as part of the Pentavalent/DPT vaccine at 6, 10, and 14 weeks, with boosters at 16-24 months and 5-6 years.

Question 285: A baby is brought for immunization for the first time at 18 months of age. Which vaccine(s) can be administered?

A. Pentavalent vaccine
B. DPT booster and OPV (Correct Answer)
C. Pentavalent, OPV, DPT, Measles and mumps
D. BCG plus OPV

Explanation: ### Explanation The core concept here is the **upper age limit** for specific vaccines under the National Immunization Schedule (NIS) in India. **1. Why Option B is Correct:** At 18 months, the child has crossed the age limit for the primary series of the Pentavalent vaccine (which must be completed by 12 months). According to the NIS, if a child presents late (between 1–7 years) and is unimmunized, we initiate the **DPT booster** (as the primary dose) and **OPV**. Since the child is 18 months old, they fall perfectly into the window for the first DPT booster (16–24 months) and the OPV booster. **2. Why the other options are incorrect:** * **Option A (Pentavalent):** The Pentavalent vaccine (DPT + Hep B + Hib) has a strict upper age limit of **12 months**. Beyond one year, the Hepatitis B and Hib components are generally not administered in the routine public health schedule. * **Option C (Pentavalent, OPV, DPT, Measles, Mumps):** This is incorrect because Pentavalent cannot be given after 1 year. Additionally, the NIS uses the **MR (Measles-Rubella)** vaccine, not the Mumps vaccine. * **Option D (BCG plus OPV):** The upper age limit for the **BCG vaccine is 1 year**. If a child is older than 12 months, BCG is no longer administered as per the National Guidelines. **3. High-Yield Clinical Pearls for NEET-PG:** * **BCG:** Limit is 1 year. (Dose: 0.05ml until 1 month; 0.1ml thereafter). * **Pentavalent/Rotavirus/Fractional IPV:** Limit is 1 year. * **Measles/MR:** Can be given up to 5 years of age. * **DPT:** Can be given up to 7 years of age. (Beyond 7 years, use Td). * **OPV:** Can be given up to 5 years of age. * **Vitamin A:** Can be given up to 5 years of age.

Question 286: Which of the following vaccines is stored in a freezer?

A. Diphtheria-Tetanus (DT)
B. Intradermal Tetanus (IT)
C. Diphtheria-Tetanus-Pertussis (DPT)
D. Measles (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Measles** **1. Why Measles is the Correct Answer:** Vaccines are categorized based on their sensitivity to temperature. **Measles, Mumps, and Rubella (MMR)**, along with **Oral Polio Vaccine (OPV)** and **Varicella**, are live-attenuated vaccines that are highly heat-sensitive but stable at sub-zero temperatures. In the cold chain system, these vaccines are ideally stored in the **freezer compartment** (at -15°C to -25°C) at the district level and above to maintain their potency. While they can be stored at +2°C to +8°C for short durations at the PHC level, they are fundamentally "freeze-stable" and "heat-labile." **2. Why the Other Options are Incorrect:** * **A, B, and C (DT, TT, and DPT):** These are **adsorbed vaccines** (containing aluminum salts as adjuvants). Adsorbed vaccines are **freeze-sensitive**. If these vaccines are frozen, the adjuvant precipitates, leading to a loss of potency and an increased risk of sterile abscesses upon injection. Therefore, they must **never** be stored in a freezer and are kept strictly between +2°C and +8°C. **3. NEET-PG High-Yield Clinical Pearls:** * **Most Heat-Sensitive Vaccine:** Oral Polio Vaccine (OPV), followed by Measles. * **Most Heat-Resistant Vaccine:** Tetanus Toxoid (TT). * **The Shake Test:** This is a bedside test used to determine if a freeze-sensitive vaccine (like DPT or TT) has been damaged by accidental freezing. If the vaccine remains cloudy or settles slowly compared to a control, it is safe; if it settles rapidly with a sediment, it must be discarded. * **ILR (Ice-Lined Refrigerator) Configuration:** In an ILR, OPV and Measles are kept at the bottom (coldest part), while DPT, TT, and Hepatitis B are kept at the top to prevent freezing.

Question 287: Normal saline is used as a diluent in which vaccine?

A. Measles
B. Rubella
C. BCG (Correct Answer)
D. Hepatitis A vaccine (HAV)

Explanation: **Explanation:** The correct answer is **BCG (Bacillus Calmette–Guérin)**. Diluents are specific liquids used to reconstitute freeze-dried (lyophilized) vaccines. Using the wrong diluent can lead to vaccine failure or increased adverse events. **1. Why BCG is correct:** BCG is a live attenuated vaccine supplied in a freeze-dried form. It must be reconstituted with **Normal Saline (0.9% NaCl)**. Normal saline is used because it maintains the isotonicity of the solution, ensuring the viability of the live *Mycobacterium bovis* bacilli. Distilled water is strictly avoided for BCG as it can cause lysis of the bacteria due to osmotic shock. **2. Why other options are incorrect:** * **Measles and Rubella (MR):** These vaccines are reconstituted using **Sterile Water for Injection (SWFI)**. Unlike BCG, the stability of the Measles/Rubella virus is better maintained in sterile water. * **Hepatitis A (HAV):** This is typically a liquid vaccine (inactivated) and does not require reconstitution with a diluent. **High-Yield Clinical Pearls for NEET-PG:** * **Storage & Disposal:** Once reconstituted, BCG and Measles vaccines must be kept on an ice pack and used within **4 hours**. Any remaining vaccine must be discarded to prevent contamination (e.g., *Staphylococcal* Toxic Shock Syndrome). * **JE Vaccine:** The Japanese Encephalitis (live) vaccine uses a specific **Phosphate Buffered Solution** as a diluent. * **Rotavirus (Rotavac):** Uses a **Citrate Phosphate Bicarbonate** diluent to neutralize gastric acid. * **Site of BCG:** Left upper arm (deltoid) via the intradermal route; it leaves a permanent scar which serves as a marker of prior vaccination.

Question 288: The Japanese encephalitis vaccine is:

A. Live attenuated (Correct Answer)
B. Inactivated toxoid
C. Cellular fractions
D. Combined

Explanation: **Explanation:** The correct answer is **A. Live attenuated**. In India, the Japanese Encephalitis (JE) vaccine used under the Universal Immunization Programme (UIP) is the **SA 14-14-2 strain**, which is a live attenuated vaccine. It is derived from the primary hamster kidney cell culture and is highly effective in providing long-term immunity. **Why the other options are incorrect:** * **Inactivated toxoid:** Toxoids (like Tetanus and Diphtheria) are modified toxins. JE is caused by a virus, not a toxin. While inactivated (killed) JE vaccines exist (e.g., Jenvac, Ixiaro), they are not "toxoids." * **Cellular fractions:** These are subunit vaccines (like Hepatitis B or Hib). JE vaccines use the whole virus (either live-weakened or killed), not just a fraction or surface antigen. * **Combined:** Combined vaccines refer to preparations like DPT or MMR. The JE vaccine is currently administered as a monovalent (standalone) injection in the national schedule. **High-Yield Clinical Pearls for NEET-PG:** * **Schedule:** Under UIP, two doses are given subcutaneously: the 1st dose at **9 completed months** (along with MR 1st dose) and the 2nd dose at **16–24 months** (along with MR 2nd dose). * **Route & Dose:** 0.5 ml, Subcutaneous (Right upper arm). * **Strain:** The SA 14-14-2 strain is imported from China. * **Endemicity:** It is only administered in **197 endemic districts** in India (primarily in states like UP, Bihar, West Bengal, and Assam). * **Contraindication:** Since it is a live vaccine, it is contraindicated in pregnancy and immunocompromised individuals.

Question 289: Which of the following vaccines is administered subcutaneously?

A. BCG
B. Polio
C. DPT
D. Measles (Correct Answer)

Explanation: **Explanation:** The route of administration for vaccines is determined by the vaccine's formulation and the desired immune response. **Measles (and MMR/MR)** vaccines are live-attenuated vaccines traditionally administered via the **subcutaneous (SC)** route, usually over the right upper arm. This route allows for a slower absorption rate compared to intramuscular injections, which is optimal for the specific immunological processing required by the measles virus. **Analysis of Incorrect Options:** * **A. BCG (Bacillus Calmette–Guérin):** Administered strictly **Intradermally (ID)** using an insulin or tuberculin syringe. This is crucial to induce a local delayed-type hypersensitivity reaction and to prevent the formation of deep abscesses. * **B. Polio:** The Oral Polio Vaccine (OPV) is given **Orally**, while the Inactivated Polio Vaccine (IPV) is administered either **Intramuscularly (IM)** or **Intradermally (fIPV)** depending on the national schedule. * **C. DPT (Diphtheria, Pertussis, Tetanus):** Administered **Intramuscularly (IM)**. In infants, the preferred site is the anterolateral aspect of the mid-thigh to avoid sciatic nerve injury and ensure deep muscle deposition, which reduces local irritation from the adjuvant (alum). **High-Yield Clinical Pearls for NEET-PG:** * **Subcutaneous Vaccines:** Measles, Mumps, Rubella (MMR), Yellow Fever, and Varicella. * **Intradermal Vaccines:** BCG, fIPV, and Rabies (Post-exposure prophylaxis - IDRV regimen). * **Intramuscular Vaccines:** DPT, Pentavalent, Hepatitis B, TT/Td, and PCV. * **Site Fact:** Measles is typically given in the **Right upper arm**, while BCG is given in the **Left upper arm** (to maintain uniformity for scar inspection).

Question 290: Which of the following vaccines can be used in pregnancy in normal circumstances?

A. MMR vaccine
B. Varicella vaccine
C. Influenza trivalent vaccine (Correct Answer)
D. Hepatitis A vaccine

Explanation: **Explanation:** The fundamental principle of immunization during pregnancy is the avoidance of **Live Attenuated Vaccines** due to the theoretical risk of the vaccine virus crossing the placenta and causing fetal infection or congenital anomalies. **Why Influenza Trivalent Vaccine is Correct:** The **Inactivated Influenza Vaccine (IIV)** is a killed vaccine and is highly recommended for all pregnant women during any trimester. Pregnancy increases the risk of severe complications from influenza (like pneumonia) due to physiological changes in the respiratory and immune systems. Vaccination not only protects the mother but also provides passive immunity to the newborn via transplacental antibody transfer, protecting the infant during the first six months of life. **Analysis of Incorrect Options:** * **MMR (Measles, Mumps, Rubella):** This is a live attenuated vaccine. Rubella components, in particular, pose a risk of Congenital Rubella Syndrome (CRS). It is contraindicated in pregnancy, and women are advised to avoid conception for 4 weeks after receiving it. * **Varicella Vaccine:** This is a live attenuated vaccine. It is contraindicated due to the theoretical risk of Congenital Varicella Syndrome. * **Hepatitis A Vaccine:** While it is an inactivated vaccine, it is not used in "normal circumstances." It is only indicated in pregnancy if there is a high risk of exposure or underlying chronic liver disease. **High-Yield Clinical Pearls for NEET-PG:** * **Safe in Pregnancy:** Tdap (Tetanus, Diphtheria, Pertussis), Inactivated Influenza, and Hepatitis B (if indicated). * **Contraindicated:** MMR, Varicella, Yellow Fever, Oral Polio (OPV), and BCG. * **Tetanus Toxoid (TT/Td):** The most common vaccine administered in pregnancy to prevent Neonatal Tetanus. * **Rule of Thumb:** Killed/Inactivated vaccines and Toxoids are generally safe; Live vaccines are contraindicated.

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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