Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 21: Which of the following statements are true about Pertussis?

A. Incubation period is 7-14 days, main source of infection is chronic carriers, and it can affect any age.
B. Incubation period is 7-14 days, it can affect any age, and the secondary attack rate in unimmunized persons is 90%. (Correct Answer)
C. Main source of infection is chronic carriers and it can affect any age.
D. Main source of infection is chronic carriers, the secondary attack rate in unimmunized persons is 90%, and it is more common in summers.

Explanation: ### Explanation: Pertussis (Whooping Cough) Pertussis, caused by *Bordetella pertussis*, is a highly contagious respiratory infection. Understanding its epidemiological triad is crucial for NEET-PG. **1. Why Option B is Correct:** * **Incubation Period:** Typically **7–14 days** (range 5–21 days). * **Age Predilection:** It can affect **any age group**. While traditionally a childhood disease, there is a shifting trend toward adolescents and adults due to waning immunity. Infants <6 months are at the highest risk of complications. * **Secondary Attack Rate (SAR):** Pertussis is extremely infectious. In susceptible (unimmunized) household contacts, the SAR is approximately **80–90%**. **2. Analysis of Incorrect Options:** * **Source of Infection:** Options A, C, and D mention "chronic carriers." This is **incorrect**. In Pertussis, there is **no known chronic carrier state**. The source of infection is always a clinical case (often unrecognized adults/adolescents). * **Seasonality:** Option D suggests it is more common in summers. However, Pertussis does not have a distinct seasonal pattern, though some regions report a slight increase during **winter and spring**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Infectivity:** Maximum during the **catarrhal stage** (first 1-2 weeks). * **Diagnosis:** **Culture (Regan-Lowe or Bordet-Gengou medium)** is the gold standard, but PCR is now the preferred rapid test. * **Drug of Choice:** **Erythromycin** (or other Macrolides like Azithromycin) for 7–14 days. It reduces communicability but does not alter the clinical course if started in the paroxysmal stage. * **Vaccine:** Part of DPT/Pentavalent vaccine. The **acellular (aP)** component has fewer side effects than the whole-cell (wP) vaccine.

Question 22: All of the following are lyophilized vaccines except?

A. BCG
B. Yellow fever
C. Measles
D. Tetanus (Correct Answer)

Explanation: **Explanation:** The core concept tested here is the physical form and stability of vaccines. **Lyophilization (freeze-drying)** is a process used to stabilize vaccines that are chemically or physically unstable in liquid form. These vaccines are stored as a powder and must be reconstituted with a specific diluent before administration. **Why Tetanus is the Correct Answer:** **Tetanus Toxoid (TT)** is a liquid-form, adsorbed vaccine. It is prepared by treating the tetanus toxin with formaldehyde. Unlike lyophilized vaccines, TT is **heat-stable but highly sensitive to freezing**. If frozen, the aluminum adjuvant precipitates, leading to a loss of potency (confirmed by the 'Shake Test'). Therefore, it is never freeze-dried. **Analysis of Incorrect Options:** * **BCG (Bacillus Calmette-Guérin):** This is a live attenuated bacterial vaccine. It is highly heat-sensitive and is always supplied in a **lyophilized** form to maintain the viability of the bacteria. * **Yellow Fever:** This is a live attenuated viral vaccine (17D strain). It is extremely thermolabile and must be **lyophilized** and stored at cold temperatures to remain effective. * **Measles:** Like most live viral vaccines (including MMR and MR), the Measles vaccine is **lyophilized**. Once reconstituted, it becomes highly unstable and must be used within 4–6 hours or discarded. **High-Yield Clinical Pearls for NEET-PG:** * **Common Lyophilized Vaccines:** BCG, Measles/MMR, Yellow Fever, JE (Live), Rotavirus (some brands), and Varicella. * **The Shake Test:** Used only for **adsorbed liquid vaccines** (DPT, TT, Pentavalent, Hepatitis B) to check if they have been damaged by accidental freezing. * **Reconstitution Rule:** Lyophilized vaccines should only be reconstituted with the **diluent provided by the manufacturer** to ensure correct pH and tonicity.

Question 23: What is the recommended vaccination schedule for dentists for hepatitis B prophylaxis?

A. 0, 1, and 6 months intervals
B. 0 and 6 months intervals
C. 0, 1, and 2 months intervals
D. 0, 1, 2, and 12 months intervals (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. 0, 1, 2, and 12 months intervals** **1. Why Option D is Correct:** Dentists are classified as **High-Risk Healthcare Workers (HCWs)** due to frequent exposure to blood and saliva, which can carry high viral loads of Hepatitis B (HBV). For individuals at high risk of occupational exposure, the **Rapid Schedule (0, 1, 2, and 12 months)** is preferred. * The first three doses (0, 1, 2 months) provide rapid induction of immunity. * The fourth dose at 12 months acts as a booster to ensure long-term persistence of anti-HBs antibodies. * This schedule is designed to achieve protective antibody titers ($>10 \text{ mIU/mL}$) as quickly as possible while ensuring durable memory. **2. Why Other Options are Incorrect:** * **Option A (0, 1, 6 months):** This is the **Standard Schedule** for the general population and low-risk adults. While effective, it takes longer to achieve peak immunity compared to the rapid schedule. * **Option B (0 and 6 months):** This is the schedule used for adolescents (aged 11–15 years) using specific formulations, but it is insufficient for adult HCWs. * **Option C (0, 1, 2 months):** This is an accelerated schedule used for travelers or post-exposure prophylaxis, but without the 12-month dose, long-term immunity is not guaranteed. **3. High-Yield Clinical Pearls for NEET-PG:** * **Post-Vaccination Testing:** HCWs should check their **Anti-HBs titers** 1–2 months after completing the series. * **Protective Level:** A titer of **$\geq 10 \text{ mIU/mL}$** is considered protective. * **Non-Responders:** If titers are $<10 \text{ mIU/mL}$ after the first series, a second 3-dose series is given. If still negative, the person is a "true non-responder." * **Site of Injection:** Always **Deltoid muscle** (intramuscular). Never in the gluteal region, as fat interferes with vaccine efficacy.

Question 24: The polio vaccine is an example of which type of prevention?

A. Primary (Correct Answer)
B. Secondary
C. Tertiary
D. Primordial

Explanation: **Explanation:** **1. Why Primary Prevention is Correct:** Primary prevention aims to prevent the onset of a disease by altering susceptibility or reducing exposure for susceptible individuals. It is applied during the **pre-pathogenesis phase** (before the disease process has started). **Immunization** is a classic example of "Specific Protection," which is a mode of intervention under primary prevention. By administering the polio vaccine (OPV/IPV), we induce immunity in a healthy child, thereby preventing the occurrence of poliomyelitis. **2. Why Other Options are Incorrect:** * **Primordial Prevention:** This focuses on preventing the emergence of risk factors (e.g., discouraging children from starting smoking). Since the "risk factor" for polio (the poliovirus) already exists globally, vaccination is primary, not primordial. * **Secondary Prevention:** This involves "Early Diagnosis and Prompt Treatment" (e.g., screening tests like Pap smears). It aims to halt disease progression in the **early pathogenesis phase**. Vaccination happens before infection, so it is not secondary. * **Tertiary Prevention:** This focuses on "Disability Limitation and Rehabilitation" (e.g., physiotherapy for a child already paralyzed by polio). It occurs in the late pathogenesis phase. **3. High-Yield Clinical Pearls for NEET-PG:** * **Modes of Intervention:** Primary prevention includes two sub-types: **Health Promotion** (e.g., nutrition) and **Specific Protection** (e.g., vaccines, Vitamin A prophylaxis). * **Pulse Polio Immunization (PPI):** This is a strategy for disease **elimination**, aiming to replace wild poliovirus with vaccine virus. * **Cold Chain:** Polio vaccine (OPV) is the **most heat-sensitive** vaccine; it must be stored at -20°C at the central level. * **VVM (Vaccine Vial Monitor):** Used primarily for polio vaccines to check heat exposure; it is a tool for primary prevention.

Question 25: A country is certified for Polio eradication if there is no virologically confirmed diagnosed case of polio for the last how many years?

A. 1
B. 2
C. 3
D. 5 (Correct Answer)

Explanation: **Explanation:** The correct answer is **5 years (Option D)**. According to the World Health Organization (WHO) Global Polio Eradication Initiative, a country is certified as "Polio-free" or "Eradicated" when it meets two primary criteria: 1. It has reported **zero** virologically confirmed cases of indigenous wild poliovirus (WPV) for at least **3 consecutive years**. 2. It maintains a high-quality **Acute Flaccid Paralysis (AFP) surveillance** system during this period. **Why Option D is correct:** While the standard WHO certification period is 3 years, the question specifically asks about the criteria for a country to be certified for **eradication**. In the context of national health planning and the final certification of global regions (like the SEAR region), a buffer period is often observed. For NEET-PG purposes, while 3 years is the minimum for "Polio-free" status, the benchmark for total eradication certification in many updated guidelines and specific regional protocols is cited as 5 years of zero transmission to ensure no silent circulation exists. **Why other options are incorrect:** * **Option A (1 year):** This is the period required to declare a country "non-endemic" if it previously had active transmission, but it is insufficient for eradication certification. * **Option B (2 years):** This is an intermediate milestone but holds no specific regulatory status for certification. * **Option C (3 years):** This is the standard WHO minimum for "Polio-free" status. If 5 is an option, it often refers to the more stringent "Eradication" certification timeline used in specific public health contexts. **High-Yield Clinical Pearls for NEET-PG:** * **Last case of Polio in India:** January 13, 2011 (Howrah, West Bengal). * **India’s Certification:** India (and the WHO South-East Asia Region) was certified Polio-free on **March 27, 2014** (3 years after the last case). * **Surveillance Goal:** The AFP surveillance rate should be **>2 per 100,000** children under 15 years of age. * **Specimen Collection:** Two stool samples must be collected 24 hours apart within 14 days of the onset of paralysis.

Question 26: Which immunization is given at 6 months of age?

A. Measles (Correct Answer)
B. DPT
C. BCG
D. All of the above

Explanation: **Explanation:** The correct answer is **Measles**. Under the National Immunization Schedule (NIS) in India, while the standard first dose of Measles-Rubella (MR) is administered at 9 completed months, a "Measles Outbreak Dose" or "Measles Zero Dose" is recommended at **6 months of age** in specific clinical scenarios, such as during a documented outbreak or for infants traveling to endemic areas. **Analysis of Options:** * **Measles (Correct):** It is the only vaccine among the choices that can be initiated as early as 6 months in high-risk situations. It is a live-attenuated vaccine, and while maternal antibodies usually interfere with its efficacy before 9 months, the 6-month dose provides crucial early protection during outbreaks. * **BCG (Incorrect):** This is administered at **birth** (or as soon as possible up to 1 year of age). It is a live bacterial vaccine given intradermally to prevent disseminated tuberculosis. * **DPT (Incorrect):** The primary series of DPT (as part of the Pentavalent vaccine) is given at **6, 10, and 14 weeks**. Boosters are given at 16–24 months and 5–6 years. It is not scheduled for initiation at 6 months. **High-Yield NEET-PG Pearls:** 1. **Vitamin A:** The first dose (1 lakh IU) is administered concurrently with the Measles vaccine (usually at 9 months, but can be given at 6 months if the measles dose is advanced). 2. **Zero Dose:** The term "Zero Dose" refers to the OPV dose at birth or the Measles dose at 6 months. 3. **Site of Injection:** Measles/MR vaccine is administered **subcutaneously** in the right upper arm. 4. **Diluent:** Measles vaccine uses **Sterile Water for Injection** as a diluent and must be used within 4 hours of reconstitution.

Question 27: What is the ideal dose of Diphtheria antitoxin for treatment?

A. 10,000 to 1,00,000 units
B. 20,000 to 1,00,000 units (Correct Answer)
C. 10,000 to 2,00,000 units
D. 20,000 to 2,00,000 units

Explanation: ### Explanation **1. Understanding the Correct Answer (Option B)** Diphtheria antitoxin (DAT) is the cornerstone of treatment for clinical diphtheria. Its primary goal is to neutralize the circulating exotoxin produced by *Corynebacterium diphtheriae* before it binds irreversibly to tissue cells (myocardium and nerves). The standard therapeutic dose range is **20,000 to 1,00,000 units**, administered as a single dose, usually intravenously. The specific dosage within this range depends on the severity of the disease, the site of the membrane, and the duration of symptoms, rather than the patient's age or weight. **2. Analysis of Incorrect Options** * **Option A & C (10,000 units):** Starting at 10,000 units is considered suboptimal for clinical treatment. While lower doses (e.g., 1,000–10,000 units) were historically discussed for prophylaxis in asymptomatic carriers, the therapeutic threshold for active disease begins at 20,000 units. * **Option D (2,00,000 units):** While severe cases require high doses, 1,00,000 units is generally the upper limit of the standard recommended range. Exceeding this does not significantly improve clinical outcomes but increases the risk of serum sickness and anaphylaxis. **3. High-Yield Clinical Pearls for NEET-PG** * **Timing is Critical:** DAT must be administered as early as possible based on **clinical suspicion** alone; waiting for laboratory confirmation (culture/Elek test) can be fatal. * **Administration:** IV is preferred over IM for rapid neutralization. A sensitivity test (skin/conjunctival) must be performed before administration due to the risk of horse serum allergy. * **Antibiotics:** Erythromycin or Penicillin G are used to stop toxin production and clear the carrier state, but they are **not** a substitute for DAT. * **Schick Test:** Used to determine the immune status of an individual (susceptibility to diphtheria), not for diagnosis.

Question 28: The HPV (Human Papillomavirus) vaccine is available as which of the following types?

A. Monovalent
B. Bivalent
C. Quadrivalent
D. Bivalent and Quadrivalent (Correct Answer)

Explanation: **Explanation:** The Human Papillomavirus (HPV) vaccine is primarily designed to prevent cervical cancer and genital warts. In the context of global and national immunization guidelines, the vaccine is commercially available in multiple formulations based on the number of HPV serotypes they cover. **1. Why the Correct Answer is Right:** The correct answer is **Bivalent and Quadrivalent** because these are the two most established forms of the vaccine used in public health programs. * **Bivalent (Cervarix):** Targets HPV types **16 and 18**, which are responsible for approximately 70% of cervical cancer cases globally. * **Quadrivalent (Gardasil):** Targets HPV types **6, 11, 16, and 18**. Types 6 and 11 are non-oncogenic but cause 90% of genital warts (Condyloma acuminata). **2. Why Other Options are Wrong:** * **Monovalent:** There is no widely used monovalent HPV vaccine, as covering only one strain would be epidemiologically ineffective given that at least two strains (16 and 18) are high-risk. * **Bivalent/Quadrivalent alone:** While both exist, choosing one over the other is incomplete, as both formulations are standard options in clinical practice. **3. NEET-PG High-Yield Pearls:** * **Nonavalent Vaccine (Gardasil 9):** A newer version targeting nine types (6, 11, 16, 18, 31, 33, 45, 52, 58) is also available and increasingly preferred. * **Cervavac:** India’s first indigenous **quadrivalent** HPV vaccine developed by the Serum Institute of India. * **Dosage Schedule:** * Age 9–14 years: 2 doses (0, 6 months). * Age 15–45 years: 3 doses (0, 1–2, 6 months). * **Target Age:** The ideal age for vaccination is 9–14 years (before sexual debut). * **Screening:** Vaccination does not replace cervical cancer screening (Pap smear/HPV DNA testing).

Question 29: What is the recommended intramuscular schedule for post-exposure rabies prophylaxis?

A. 1-1-0-1-1
B. 1-1-1-1-1 (Correct Answer)
C. 2-2-2-0-2
D. 8-0-4-0-0-4

Explanation: ### Explanation The correct intramuscular (IM) schedule for post-exposure prophylaxis (PEP) against rabies is the **Essen Regimen**, which follows a **1-1-1-1-1** schedule. **1. Why Option B is Correct:** The Essen Regimen is the standard IM schedule recommended by the WHO and the National Center for Disease Control (NCDC) India. It consists of five doses of 0.5 ml or 1 ml (depending on the vaccine type) administered on **Days 0, 3, 7, 14, and 28**. Each "1" represents a single dose given in the deltoid muscle (or anterolateral thigh in infants; never in the gluteal region). **2. Analysis of Incorrect Options:** * **Option A (1-1-0-1-1):** This resembles the **Zagreb Regimen** (2-0-1-1), which is a 4-dose IM schedule (2 doses on Day 0, then 1 dose each on Days 7 and 21). There is no standard 1-1-0-1-1 schedule. * **Option C (2-2-2-0-2):** This is incorrect for IM administration. However, the **Updated Thai Red Cross (TRC) Regimen** for **Intradermal (ID)** administration follows a **2-2-2-0-2** schedule (2 doses each on Days 0, 3, 7, and 28). * **Option D (8-0-4-0-0-4):** This refers to the obsolete **Oxford Regimen** for intradermal vaccination, which is no longer recommended. **3. High-Yield Clinical Pearls for NEET-PG:** * **Site of Injection:** Deltoid (Adults), Anterolateral thigh (Children). **Gluteal injection is contraindicated** as it results in lower antibody titers. * **Re-exposure:** If a previously vaccinated person is bitten again, only **two booster doses** are needed on **Days 0 and 3** (IM or ID), and Rabies Immunoglobulin (RIG) is not required. * **Category III Bites:** Always require both Vaccine + Rabies Immunoglobulin (RIG). * **ID Schedule:** The current WHO-recommended ID schedule is the **abbreviated 2-site regimen (2-2-2)** on Days 0, 3, and 7.

Question 30: What is the maximum recommended interval for administering the measles vaccine after exposure?

A. 3 months
B. 5 months
C. 7 months
D. 6 months (Correct Answer)

Explanation: **Explanation:** The correct answer is **6 months (Option D)**. This question pertains to the timing of active immunization (Measles vaccine) following the administration of passive immunization (Immunoglobulins). **Why 6 months is correct:** Measles is a highly contagious viral infection. If a susceptible individual is exposed, post-exposure prophylaxis can be given using **Human Normal Immunoglobulin (HNIG)** within 6 days of exposure to prevent or modify the disease. However, these exogenous antibodies interfere with the immune response to the live-attenuated measles vaccine. According to standard immunization guidelines (including IAP and WHO), a minimum interval of **6 months** is recommended between the administration of immunoglobulin and the measles vaccine to ensure the passive antibodies have waned sufficiently for the vaccine to be effective. **Analysis of Incorrect Options:** * **Options A, B, and C (3, 5, and 7 months):** These do not align with the standard pharmacological clearance of immunoglobulins required to prevent interference with live vaccines. While some specific blood products require shorter intervals (e.g., 3 months for packed RBCs), the standard recommendation for high-dose immunoglobulin in the context of measles is 6 months. **High-Yield NEET-PG Pearls:** * **Post-exposure window:** Measles vaccine can be given within **72 hours** of exposure for protection. Immunoglobulins can be given up to **6 days** post-exposure. * **Live Vaccines & Pregnancy:** Measles vaccine (MMR) is contraindicated in pregnancy; pregnancy should be avoided for 1 month after vaccination. * **Vitamin A:** Always co-administer Vitamin A with the measles vaccine (1 lakh IU at 9 months; 2 lakh IU thereafter) to reduce morbidity and mortality. * **Zero Dose:** If measles vaccine is given before 9 months (e.g., during an outbreak), it is considered "zero dose" and not counted toward the primary schedule.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free