Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 131: For how long can vaccines be stored at a Primary Health Centre (PHC)?

A. 2 days
B. 7 days
C. 15 days
D. 30 days (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. 30 days** In the Indian Universal Immunization Programme (UIP) cold chain system, the duration of vaccine storage is determined by the level of the healthcare facility. A **Primary Health Centre (PHC)** is equipped with an **Ice-Lined Refrigerator (ILR)** and a Deep Freezer (small). According to standard guidelines, vaccines can be stored at the PHC level for a maximum of **one month (30 days)**. This duration ensures a balance between maintaining vaccine potency and managing supply logistics from the district level. **Analysis of Incorrect Options:** * **A & B (2 days / 7 days):** These durations are too short for a PHC. However, 48–72 hours is the typical duration vaccines are kept in **vaccine carriers** during outreach sessions or "sub-centre" activities. * **C (15 days):** While some regional guidelines previously suggested shorter intervals, the standard UIP protocol for PHCs remains 30 days. 15 days is not a standard benchmark for any specific level of the cold chain. **High-Yield Clinical Pearls for NEET-PG:** * **Storage Levels & Durations:** * **Regional/State Level (GMSD):** 3 months. * **District Level:** 1 month. * **PHC Level:** 1 month. * **Sub-centre/Session Site:** 48–72 hours (in vaccine carriers). * **Temperature Maintenance:** At the PHC, ILRs maintain a temperature of **+2°C to +8°C**, which is ideal for most vaccines (including Tseries, HepB, and DPT). * **The "Shake Test":** Used to determine if a freeze-sensitive vaccine (like DPT, TT, or Pentavalent) has been damaged by sub-zero temperatures. * **Most Heat Sensitive Vaccine:** Oral Polio Vaccine (OPV). * **Most Heat Resistant Vaccine:** Tetanus Toxoid (TT).

Question 132: Which vaccines are contraindicated in an HIV-positive child?

A. Oral Polio Vaccine (OPV) (Correct Answer)
B. Measles, Mumps, and Rubella (MMR) vaccine
C. Rabies vaccine
D. Influenza vaccine

Explanation: ### Explanation The core principle in vaccinating HIV-positive children is the distinction between **live-attenuated** and **inactivated** vaccines. In immunocompromised states, live vaccines pose a risk of vaccine-derived disease due to uncontrolled viral replication. **1. Why OPV is the Correct Answer:** According to WHO and National Immunization Guidelines, **Oral Polio Vaccine (OPV)** is strictly contraindicated in HIV-positive children and their household contacts. This is because the live-attenuated Sabin virus can undergo prolonged excretion, potentially causing **Vaccine-Associated Paralytic Poliomyelitis (VAPP)** in the child or circulating vaccine-derived poliovirus (cVDPV) in the community. **Inactivated Polio Vaccine (IPV)** is the safe and recommended alternative. **2. Analysis of Incorrect Options:** * **MMR (Option B):** While MMR is a live vaccine, it is **not** contraindicated unless the child is *severely* immunocompromised (CD4 count <15%). In asymptomatic or mildly symptomatic HIV cases, MMR is recommended because the risk of natural measles (which is often fatal in HIV) outweighs the risk of the vaccine. * **Rabies Vaccine (Option C):** This is a **killed/inactivated** vaccine. It is safe for HIV-positive individuals. In post-exposure prophylaxis, it is mandatory regardless of immune status. * **Influenza Vaccine (Option D):** The injectable form is an **inactivated** vaccine and is actually recommended annually for HIV patients to prevent respiratory complications. (Note: The *nasal spray* flu vaccine is live and should be avoided). **3. NEET-PG High-Yield Pearls:** * **BCG:** Contraindicated in symptomatic HIV/AIDS due to the risk of disseminated BCG-osis. * **Yellow Fever:** Generally contraindicated in HIV. * **Rule of Thumb:** In HIV, "Killed vaccines are safe; Live vaccines depend on the CD4 count" (except OPV and BCG, which are generally avoided). * **Household Contacts:** If a family member is HIV-positive, the child should receive IPV instead of OPV to prevent horizontal transmission of the vaccine virus.

Question 133: Who among the following discovered smallpox vaccination?

A. John Hunter
B. Louis Pasteur
C. Edward Jenner (Correct Answer)
D. James Lind

Explanation: **Explanation:** The correct answer is **Edward Jenner (Option C)**. In 1796, Jenner observed that milkmaids who had contracted cowpox (a milder disease) appeared immune to smallpox. He tested this hypothesis by inoculating a young boy, James Phipps, with material from a cowpox lesion and subsequently exposing him to smallpox. The boy did not develop the disease. This pioneered the concept of **vaccination** (derived from the Latin word *vacca*, meaning cow). Jenner is widely regarded as the "Father of Immunology." **Analysis of Incorrect Options:** * **John Hunter (A):** A renowned British surgeon and teacher to Edward Jenner. While he made significant contributions to anatomy and surgery, he did not discover the smallpox vaccine. * **Louis Pasteur (B):** Known as the "Father of Microbiology," Pasteur developed vaccines for **Rabies, Anthrax, and Fowl Cholera**. He also formulated the Germ Theory of Disease and the process of pasteurization. * **James Lind (D):** A Scottish physician who conducted one of the first clinical trials and discovered that citrus fruits (Vitamin C) could cure and prevent **Scurvy**. **High-Yield Clinical Pearls for NEET-PG:** * **Smallpox Eradication:** Smallpox is the only human infectious disease to be eradicated. * **Last Case:** The last naturally occurring case was reported in **Somalia (1977)**. * **Global Eradication:** Officially 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" technique in smallpox vaccination.

Question 134: Which of the following statements about pertussis is false?

A. Fomites play a small role in the spread of the disease.
B. Maternal antibodies provide protection in infants and fomites play a small role in the spread of the disease. (Correct Answer)
C. Maternal antibodies provide protection in infants and the disease is commonly seen in infants.
D. Maternal antibodies provide protection in infants and fomites play a small role in the spread of the disease.

Explanation: ### Explanation The correct answer is **"Maternal antibodies provide protection in infants"** (noting that the second part of the option regarding fomites is actually a true statement, making the combined statement false due to the first half). **1. Why the Correct Answer is Right (The Medical Concept):** In Pertussis (Whooping Cough), **maternal antibodies do not provide passive immunity** to the newborn. Unlike diseases like Measles or Diphtheria, where transplacental IgG offers protection for several months, infants are born highly susceptible to *Bordetella pertussis*. This is why the disease is most severe and carries the highest mortality in infants under 6 months of age. To mitigate this risk, current guidelines (like those from the CDC and increasingly adopted globally) recommend vaccinating pregnant women with **Tdap** during the third trimester to facilitate the transfer of antibodies. **2. Analysis of Other Statements:** * **Fomites play a small role:** This is a **true** statement. Pertussis is primarily spread via direct inhalation of respiratory droplets. The organism survives poorly on environmental surfaces; hence, fomites are an insignificant route of transmission. * **Commonly seen in infants:** This is **true**. Because there is no natural passive immunity from the mother, infants are the primary risk group. * **Secondary Attack Rate (SAR):** Though not explicitly in the options, remember that Pertussis is highly contagious with a SAR of approximately **80-90%** among susceptible household contacts. **3. NEET-PG High-Yield Pearls:** * **Agent:** *Bordetella pertussis* (Gram-negative coccobacillus). * **Incubation Period:** 7–14 days (Range: 5–21 days). * **Infectivity:** Maximum during the **catarrhal stage** (the first 1-2 weeks). * **Drug of Choice:** **Erythromycin** (or other Macrolides like Azithromycin) for 7–14 days. It reduces communicability but has limited effect on clinical symptoms if started late. * **Vaccine:** Part of the Pentavalent vaccine in India (6, 10, 14 weeks). The **acellular (aP)** component has fewer side effects than the **whole-cell (wP)** component.

Question 135: If convulsions are present, which vaccine should not be administered?

A. DPT (Correct Answer)
B. Oral Polio
C. BCG
D. Tetanus toxoid

Explanation: **Explanation:** The correct answer is **DPT (Diphtheria, Pertussis, and Tetanus)**. The primary reason for this contraindication is the **Whole-cell Pertussis (wP)** component of the vaccine. Pertussis antigens are known to be neurotoxic and can trigger neurological complications, including febrile seizures, encephalopathy, or prolonged convulsions. **Why DPT is the correct answer:** In clinical practice, a history of uncontrolled seizures, progressive neurological disorders, or an evolving neurological condition is a **strict contraindication** for the pertussis component. If a child has a history of convulsions, the "Triple Vaccine" (DPT) is withheld and replaced with **DT (Diphtheria and Tetanus)** to avoid aggravating the neurological state. **Why other options are incorrect:** * **Oral Polio (OPV):** This is a live attenuated vaccine. Its primary contraindications are immunodeficiency states (e.g., HIV, hypogammaglobulinemia) or household contact with an immunocompromised person. It has no association with convulsions. * **BCG:** This is contraindicated in individuals with generalized eczema, skin infections at the site of injection, or severe immunodeficiency. It does not affect the central nervous system. * **Tetanus Toxoid (TT):** TT is generally safe. It is the pertussis component in the DPT combination that is the culprit, not the tetanus component. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindication for Pertussis:** Encephalopathy within 7 days of a previous dose. * **Alternative:** In children with a history of seizures where pertussis coverage is still desired, **acellular Pertussis (aP)** is preferred over whole-cell (wP) as it has a significantly lower risk of febrile seizures. * **DT vs. DPT:** If a child is over 7 years old or has neurological contraindications, the Pertussis component is dropped, and DT/Td is administered.

Question 136: What is the threshold level of herd immunity for Pertussis?

A. 80%
B. 70%
C. 90% (Correct Answer)
D. 50%

Explanation: **Explanation:** **1. Why 90% is Correct:** Herd immunity (community immunity) is the resistance of a group to the spread of an infectious disease based on the proportion of immune individuals. The threshold level required to stop transmission depends on the **Basic Reproduction Number ($R_0$)**—the number of secondary cases produced by one case in a susceptible population. Pertussis (Whooping Cough) is highly contagious, with an $R_0$ typically ranging from **12 to 17**. Using the formula $H = 1 - (1/R_0)$, a very high percentage of the population must be immune to achieve herd effect. For Pertussis, this threshold is approximately **90–95%**. **2. Analysis of Incorrect Options:** * **80% (Option A):** This is the threshold for diseases with lower infectivity, such as **Polio** (approx. 80%) or **Diphtheria** (approx. 85%). * **70% (Option B):** This level is insufficient for most highly communicable childhood diseases. It is closer to the threshold estimated for some strains of Influenza or the initial targets for Rubella. * **50% (Option C):** This is far below the requirement for any major vaccine-preventable disease (VPD) spread by respiratory droplets. **3. High-Yield Clinical Pearls for NEET-PG:** * **Measles** has the highest $R_0$ (12–18) and requires the highest herd immunity threshold (**94–97%**). * **Pertussis** is unique because vaccine-induced immunity wanes over time, making high coverage even more critical. * **Herd immunity does not apply to Tetanus**, as it is not transmitted from person to person (non-communicable). * **Formula for Herd Immunity Threshold ($H$):** $1 - (1/R_0)$. If $R_0$ increases, the required herd immunity also increases.

Question 137: According to the WHO-recommended Expanded Program on Immunization (EPI) Cluster sampling methodology for assessing primary immunization coverage, what is the age group of children surveyed?

A. 0-12 months
B. 6-12 months
C. 9-12 months
D. 12-23 months (Correct Answer)

Explanation: ### Explanation **1. Why Option D is Correct:** The WHO EPI Cluster Sampling technique (30 x 7 design) is specifically designed to assess **primary immunization coverage**. Primary immunization is considered complete only after a child has received all scheduled vaccines (BCG, OPV, DPT/Pentavalent, and Measles/MR) by their first birthday. Therefore, to evaluate if a child successfully completed the schedule, they must be surveyed **after** they have reached 12 months of age but before they are too old to recall or track (up to 23 months). This 12–23 month window ensures that the "denominator" consists of children who have had the full opportunity to complete the primary series. **2. Why Other Options are Incorrect:** * **Options A, B, and C (0–12 months):** Children in these age groups are still "in progress" regarding their immunization schedule. For example, the first dose of the Measles vaccine is typically given at 9 months. Surveying a 6-month-old would falsely lower coverage data because they are not yet eligible for all primary vaccines. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **The 30 x 7 Design:** This methodology involves selecting **30 clusters** (villages/wards) and surveying **7 children** in the target age group (12–23 months) from each cluster, totaling a sample size of **210**. * **Sampling Technique:** It uses **Two-Stage Stratified Cluster Sampling**. The first stage is selecting clusters (using Probability Proportional to Size), and the second stage is selecting households within the cluster. * **Primary Immunization:** In India, a child is "fully immunized" if they receive 1 dose of BCG, 3 doses of DPT (or Pentavalent), 3 doses of OPV, and 1 dose of Measles by age one. * **Recent Update:** While the classic 30x7 is the standard for exams, newer WHO guidelines (2018) suggest larger sample sizes and more complex designs for higher precision, but the 12–23 month age group remains the gold standard for primary coverage assessment.

Question 138: BCG vaccination is administered by which route?

A. Subcutaneous
B. Intradermal (Correct Answer)
C. Intramuscular
D. Subdermal

Explanation: **Explanation:** The **BCG (Bacillus Calmette-Guérin)** vaccine is a live attenuated vaccine derived from *Mycobacterium bovis*. It is administered via the **Intradermal (ID)** route, specifically over the left deltoid muscle. **Why Intradermal?** The intradermal route is chosen because it allows for a slow, localized release of the antigen, which is essential for stimulating a strong **Cell-Mediated Immunity (CMI)**. This route leads to the characteristic formation of a wheal, followed by a papule, shallow ulcer, and eventually a permanent scar. Administering it deeper can lead to complications like regional lymphadenitis or abscess formation. **Analysis of Incorrect Options:** * **Subcutaneous (A):** This route is typically used for vaccines like Measles/MRSA and Yellow Fever. If BCG is given subcutaneously, it increases the risk of local abscesses and severe lymphadenopathy. * **Intramuscular (C):** Used for killed/subunit vaccines like DPT, Hep B, and TT. BCG is never given IM as it would bypass the necessary dermal immune response. * **Subdermal (D):** This is not a standard clinical route for immunization. **High-Yield Clinical Pearls for NEET-PG:** * **Dose:** 0.05 ml for neonates (below 4 weeks) and 0.1 ml for infants above 4 weeks. * **Syringe:** A specialized **Tuberculin/Omega syringe** with a 26G needle is used. * **Diluent:** Normal Saline (NS) is the only recommended diluent. * **Site:** Left deltoid (standardized globally to avoid confusion with other scars). * **Phenomenon:** The "BCG scar" is the hallmark of successful vaccination. If a child develops a scar within 48 hours, it suggests **"Accelerated BCG reaction,"** indicating the child may already be infected with TB.

Question 139: Both active and passive immunization is given in all of the following conditions, EXCEPT:

A. Tetanus
B. Rabies
C. Measles (Correct Answer)
D. HBV

Explanation: **Explanation:** The simultaneous administration of active and passive immunization (giving both a vaccine and pre-formed antibodies/immunoglobulins) is indicated for post-exposure prophylaxis in diseases with high fatality rates or short incubation periods. **Why Measles is the Correct Answer:** Measles prophylaxis depends on the timing of exposure, but **active and passive immunization are not given together.** * **Active immunization (Measles/MMR vaccine)** is effective if given within **72 hours** of exposure. * **Passive immunization (Human Immunoglobulin)** is given to susceptible contacts (e.g., immunocompromised or infants) within **6 days** of exposure. If immunoglobulin is administered, it interferes with the live vaccine's replication; therefore, the vaccine must be delayed by 8–11 months. **Why the other options are incorrect:** * **Tetanus:** In a "tetanus-prone" wound in an unimmunized individual, both **Tetanus Toxoid (TT/Td)** and **Tetanus Immunoglobulin (TIG)** are administered at different sites to provide immediate and long-lasting protection. * **Rabies:** For Category III bites, both the **Anti-Rabies Vaccine (ARV)** and **Rabies Immunoglobulin (RIG)** are mandatory. RIG provides protection during the "window period" before the vaccine induces antibodies. * **HBV (Hepatitis B):** Following accidental needle-stick injury or perinatal exposure (mother HBsAg positive), both **Hep-B Vaccine** and **Hepatitis B Immunoglobulin (HBIG)** are administered simultaneously at different sites. **High-Yield Clinical Pearls for NEET-PG:** 1. **Site Rule:** When giving both, always use separate syringes and separate anatomical sites (e.g., right vs. left deltoid) to prevent the immunoglobulin from neutralizing the vaccine. 2. **Other Examples:** Active + Passive immunization is also used for **Diphtheria** (in unimmunized contacts) and **Varicella** (in high-risk exposures). 3. **Measles Vaccine:** It is a live attenuated vaccine (Edmonston-Zagreb strain) usually given at 9 months. If given before 9 months (e.g., during an outbreak), that dose is considered "zero dose" and not counted.

Question 140: Which vaccine is used for the prevention of Japanese Encephalitis?

A. Dengvaxia
B. BCG vaccine
C. JEV vaccine (Correct Answer)
D. Hepatitis B vaccine

Explanation: **Explanation:** **Japanese Encephalitis (JE)** is a leading cause of viral encephalitis in Asia, transmitted by the *Culex* mosquito. The correct answer is the **JEV vaccine**, which is specifically designed to provide immunity against the Japanese Encephalitis virus. * **Why JEV Vaccine is Correct:** In India, under the Universal Immunization Programme (UIP), the live attenuated **SA-14-14-2 strain** (derived from primary hamster kidney cells) is used. It is administered subcutaneously in two doses: the first at 9 months (with MR-1) and the second at 16–24 months (with DPT booster). **Analysis of Incorrect Options:** * **Dengvaxia:** This is the first licensed vaccine for **Dengue**, not JE. While both are Flaviviruses, they require specific antigens for protection. * **BCG (Bacillus Calmette-Guérin):** A live bacterial vaccine used to prevent severe forms of **Tuberculosis** (like TB meningitis and miliary TB). * **Hepatitis B Vaccine:** A subunit (recombinant) vaccine used to prevent **Hepatitis B virus** infection and its complications, such as cirrhosis and hepatocellular carcinoma. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Culex tritaeniorhynchus* (breeds in rice fields). * **Reservoir/Amplifier Host:** Pigs (Ardeid birds are the natural reservoir). * **Vaccine Strains:** Apart from the live SA-14-14-2, inactivated vaccines like **JENVAC** (indigenous) and **IXIARO** are also available. * **UIP Schedule:** JE vaccine is only administered in **endemic districts** (currently ~216 districts in India). * **Key Contraindication:** Pregnancy and immunocompromised states (for the live attenuated version).

Practice by Chapter

Principles of Immunization

Practice Questions

Types of Vaccines

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Universal Immunization Program

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Cold Chain System

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Vaccine Storage and Handling

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Adverse Events Following Immunization

Practice Questions

National Immunization Schedule

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Polio Eradication

Practice Questions

Measles Elimination

Practice Questions

Tetanus Control

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New and Underutilized Vaccines

Practice Questions

Vaccination Coverage Assessment

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