Immunization and Vaccine-Preventable Diseases Practice Questions

Q: Which one of the following doses in Loeffler units of Diphtheria Toxoid is incorporated in DPT vaccine per dose?

25. ### Explanation **1. Why Option C (25) is Correct:** The DPT (Diphtheria, Pertussis, and Tetanus) vaccine is a combination vaccine used in the Universal Immunization Programme (UIP). According to the Indian Pharmacopoeia and WHO standards, each **0.5 ml dose** of the adsorbed DPT vaccine contains: * **Diphtheria Toxoid:** 20 to 30 Lf (Loeffler units or Limit of Flocculation). The standard accepted value for competitive exams is **25 Lf**. * **Tetanus Toxoid:** 5 to 25 Lf (usually 5–10 Lf). * **B. pertussis:** ≥ 4 IU (International Units). The Lf unit measures the quantity of the toxoid based on its ability to flocculate with a specific antitoxin. 25 Lf provides the optimal balance between inducing a robust immune response and minimizing local adverse reactions. **2. Why Other Options are Incorrect:** * **Option A (5):** This is too low for the primary DPT series. However, 2–5 Lf is the dose used in the **dT (adult-type)** vaccine to reduce the risk of hypersensitivity reactions in older children and adults. * **Option B (15):** This is an intermediate value not standard for the pediatric DPT formulation. * **Option D (35):** This exceeds the standard concentration, which would significantly increase the risk of local reactions (pain, swelling, and sterile abscesses) without providing additional clinical benefit. **3. High-Yield Clinical Pearls for NEET-PG:** * **Adjuvant:** Aluminum phosphate or hydroxide is used to enhance the immunogenicity of the toxoids. * **Storage:** DPT must be stored at **+2°C to +8°C**. It should **never be frozen** (Shake Test is used to check if it was previously frozen). * **Site of Injection:** Anterolateral aspect of the mid-thigh (Intramuscular). * **Contraindication:** A history of encephalopathy within 7 days of a previous dose is an absolute contraindication for the Pertussis component.

Q: Which age group is targeted in the WHO's catch-up vaccination strategy for measles elimination?

9 months to 14 years. ### Explanation **Correct Answer: C. 9 months to 14 years** The WHO’s global strategy for measles elimination involves a four-pronged approach: high routine coverage, a "second opportunity" for vaccination, effective surveillance, and **Catch-up campaigns**. The **Catch-up vaccination strategy** is a one-time nationwide campaign targeting all children in a broad age group, regardless of their previous vaccination or disease history. The goal is to rapidly interrupt measles virus transmission by closing immunity gaps in the population. The WHO specifically recommends the age group of **9 months to 14 years** for these campaigns because this cohort represents the primary reservoir for transmission in endemic or transitioning regions. **Analysis of Incorrect Options:** * **A & D (6 months):** Routine measles vaccination (MCV1) is generally not given before 9 months because maternal antibodies can interfere with the immune response, leading to vaccine failure. 6 months is only considered during outbreaks or for displaced populations. * **B (9 months to 10 years):** While many older strategies focused on younger children, the current elimination goal requires a wider net (up to 14 years) to ensure "herd immunity" levels (>95%) are reached across the entire pediatric and adolescent population. **High-Yield Clinical Pearls for NEET-PG:** * **Follow-up Campaigns:** Conducted every 2–4 years targeting children born since the last campaign (usually **9 months to 5 years**). * **Keep-up:** Refers to maintaining >95% coverage in routine immunization (MCV1 at 9 months and MCV2 at 16–24 months). * **Vitamin A:** Administered during measles treatment to reduce mortality (1 lakh IU for 1 year). * **Measles Elimination:** Defined as the absence of endemic measles transmission in a region for ≥12 months.

Q: Regarding poliovirus responsible for poliomyelitis, all are true except:

Type 3 is most common in India. ### Explanation **1. Why Option C is the Correct Answer (The "Except" Statement):** In India, as well as globally, **Type 1 Poliovirus** has historically been the most common cause of both endemic poliomyelitis and major epidemics. Type 3 is the second most common but has never been the predominant strain in India. Therefore, the statement "Type 3 is most common in India" is factually incorrect, making it the right choice for this "except" question. **2. Analysis of Other Options:** * **Option A (Type 1 is responsible for most epidemics):** This is **True**. Type 1 is the most paralytogenic and highly infectious strain, historically responsible for the vast majority of outbreaks worldwide. * **Option B (Type 1 is most common in India):** This is **True**. Before eradication, Type 1 was the most frequently isolated serotype in the Indian subcontinent. * **Option C (Type 2 is eradicated worldwide):** This is **True**. The Global Commission for the Certification of Poliomyelitis Eradication declared Wild Poliovirus Type 2 (WPV2) eradicated in **September 2015** (last case detected in 1999). **3. High-Yield Clinical Pearls for NEET-PG:** * **Eradication Status:** * **WPV Type 2:** Eradicated (2015). * **WPV Type 3:** Eradicated (Declared in October 2019; last case seen in Nigeria, 2012). * **WPV Type 1:** Only type currently circulating (endemic in Afghanistan and Pakistan). * **India Status:** India was declared "Polio Free" by the WHO on **March 27, 2014** (Last case: Howrah, West Bengal, Jan 2011). * **Vaccine Shift:** Due to Type 2 eradication, the **trivalent OPV (tOPV)** was replaced by **bivalent OPV (bOPV)** containing only Types 1 and 3 to prevent Vaccine-Derived Poliovirus (VDPV) Type 2. * **Infectivity:** Polio is most infectious during the late incubation period and the first week of clinical illness. The virus is excreted in stools for 6–8 weeks.

Q: Cervarix vaccine for HPV contains which strains of virus?

HPV 16, 18. **Explanation:** The correct answer is **B (HPV 16, 18)**. Cervarix is a **bivalent vaccine** specifically designed to provide protection against the two most high-risk oncogenic strains of Human Papillomavirus (HPV). HPV 16 and 18 are responsible for approximately 70% of all cervical cancer cases globally. **Detailed Analysis of Options:** * **Option B (Correct):** Cervarix contains L1 proteins of HPV types 16 and 18. It is produced using recombinant DNA technology in insect cells and uses a unique adjuvant called **AS04** to enhance the immune response. * **Option A (Incorrect):** HPV 6 and 11 are low-risk strains primarily responsible for **anogenital warts** (Condyloma acuminata), not malignancy. * **Option C (Incorrect):** This describes the **Quadrivalent vaccine (Gardasil)**. Gardasil protects against types 16 and 18 (cancer prevention) as well as types 6 and 11 (wart prevention). * **Option D (Incorrect):** While types 31 and 33 are oncogenic, they are covered by the **Nonavalent vaccine (Gardasil 9)**, which includes types 6, 11, 16, 18, 31, 33, 45, 52, and 58. **High-Yield Clinical Pearls for NEET-PG:** * **Target Age:** The primary target group for the HPV vaccine is girls aged **9–14 years** (before sexual debut). * **Dosage Schedule (IAP/WHO):** * 9–14 years: 2 doses (0, 6 months). * >15 years or immunocompromised: 3 doses (0, 1–2, 6 months). * **Cervavac:** India’s first indigenous quadrivalent HPV vaccine (qHPV) manufactured by the Serum Institute of India. * **Screening:** Vaccination does not replace cervical cancer screening; Pap smears/HPV DNA testing should continue as per protocols.

Q: Active immunization following exposure is most commonly given for which of the following?

Rabies. **Explanation:** The correct answer is **Rabies**. This question tests the concept of **Post-Exposure Prophylaxis (PEP)** through active immunization. **Why Rabies is Correct:** Rabies has a uniquely long and variable incubation period (typically 1–3 months). This "window period" allows the body enough time to mount a protective immune response via **active immunization** (vaccine) before the virus reaches the Central Nervous System. In clinical practice, Rabies PEP is the most common scenario where active immunization (often combined with passive immunization/immunoglobulins) is administered *after* exposure to prevent disease onset. **Analysis of Incorrect Options:** * **Polio:** Immunization is strictly **pre-exposure** (preventative). Once exposure occurs, the virus replicates too rapidly in the gut and lymphoid tissue for post-exposure vaccination to be effective. * **Plague:** Management after exposure involves **chemoprophylaxis** (e.g., Doxycycline or Sulfonamides), not active immunization. * **Measles:** While active immunization can be given within 72 hours of exposure to provide some protection, it is not the "most common" or definitive indication compared to Rabies, where post-exposure vaccination is the standard of care globally. **High-Yield Clinical Pearls for NEET-PG:** * **Diseases where PEP includes Active Immunization:** Rabies, Hepatitis B, Tetanus, and Measles. * **Rabies Vaccine Schedule (Post-exposure):** 0, 3, 7, 14, and 28 days (Intramuscular/Essen regimen) OR 2-2-2-0-2 (Intradermal/Thai Red Cross regimen). * **Rule of Thumb:** If the incubation period of a disease is longer than the time required for the vaccine to produce antibodies (usually 7–10 days), post-exposure active immunization is theoretically possible.

Q: Which of the following vaccines is MOST sensitive to heat?

OPV. ### Explanation **Correct Option: C (OPV)** The Oral Polio Vaccine (OPV) is the **most heat-sensitive** vaccine in the entire immunization program. It is highly thermolabile and requires strict maintenance of the cold chain at -20°C for long-term storage. To monitor its potency, each vial is equipped with a **Vaccine Vial Monitor (VVM)**, which changes color when exposed to cumulative heat. **Analysis of Incorrect Options:** * **A. Measles:** While measles is a live-attenuated vaccine and is heat-sensitive, it is more stable than OPV. It must be stored at +2°C to +8°C and is highly sensitive to **light** (photo-sensitive). * **B. BCG:** BCG is also a live-attenuated vaccine. It is relatively heat-sensitive but significantly more stable than OPV. Like measles, it is highly sensitive to sunlight. * **C. IPV:** Inactivated Polio Vaccine (IPV) is more heat-stable than its oral counterpart (OPV) because it contains killed virus particles rather than live-attenuated ones. **High-Yield Clinical Pearls for NEET-PG:** * **Hierarchy of Heat Sensitivity:** (Most Sensitive) **OPV > Measles > BCG > DPT > DT > TT** (Least Sensitive/Most Heat Stable). * **Freeze Sensitivity:** While OPV is the most heat-sensitive, the **Hepatitis B** and **DPT/Pentavalent** vaccines are the most **freeze-sensitive**. They must never be frozen (the "Shake Test" is used to check if they have been damaged by freezing). * **Storage:** At the PHC level, all vaccines (including OPV and Measles) are stored in the **ILR (Ice-Lined Refrigerator)** at +2°C to +8°C for short-term use. * **Reconstitution Rule:** BCG and Measles vaccines must be used within **4 hours** of reconstitution; otherwise, they must be discarded due to the risk of Toxic Shock Syndrome (Staphylococcal contamination).

Q: The 17D vaccine is used for the prevention and control of which disease?

Yellow fever. **Explanation:** **Yellow Fever (Option A)** is the correct answer. The **17D vaccine** is a live-attenuated preparation derived from the 17D strain of the Yellow Fever virus. It is considered one of the most effective vaccines ever developed, providing long-lasting immunity (often lifelong) after a single subcutaneous dose. **Analysis of Incorrect Options:** * **Japanese Encephalitis (Option B):** Vaccines for JE include the live-attenuated **SA 14-14-2** strain (most common in India), or inactivated vaccines like JENVAC or IXIARO. * **Hemorrhagic Fever (Option C):** This is a broad category. While Yellow Fever is a type of viral hemorrhagic fever, the 17D vaccine is specific only to the Yellow Fever virus. Other hemorrhagic fevers (like Ebola or Lassa) require different specific vaccines or have none available. * **Dengue (Option D):** The most recognized vaccine is **Dengvaxia (CYD-TDV)**, which is a tetravalent live-attenuated vaccine. **High-Yield Clinical Pearls for NEET-PG:** * **Administration:** Given as a single dose (0.5 ml) subcutaneously. * **Validity:** Under International Health Regulations (IHR), the certificate of vaccination becomes valid **10 days** after vaccination and is now valid for **life**. * **Contraindications:** It is contraindicated in infants <6 months, individuals with egg allergies (as it is grown in chick embryos), and immunocompromised patients. * **Cold Chain:** It is highly heat-sensitive and must be stored between **+2°C to +8°C**.

Q: Mass immunization is indicated in all of the following conditions, except?

Leprosy. **Explanation:** The concept of **Mass Immunization** refers to the rapid administration of a vaccine to a large percentage of a population to achieve herd immunity or control an outbreak. **Why Leprosy is the correct answer:** Mass immunization is not indicated for Leprosy primarily because **there is no specific, dedicated vaccine** for it. While the BCG vaccine offers some cross-protection against *Mycobacterium leprae*, it is not used in a "mass campaign" format specifically for leprosy control. Furthermore, leprosy has a very long incubation period (2–5 years) and low infectivity; therefore, the strategy focuses on **Early Diagnosis and MDT (Multi-Drug Therapy)** rather than mass vaccination. **Analysis of incorrect options:** * **Cholera:** Indicated during outbreaks or in endemic "hotspots" and humanitarian crises to prevent rapid spread. * **Influenza:** Mass immunization is the mainstay of prevention, especially during seasonal shifts or pandemics, to protect vulnerable groups and reduce transmission. * **Tuberculosis:** BCG is administered as part of the Universal Immunization Programme (UIP) to the entire birth cohort (mass neonatal vaccination) to prevent severe childhood forms like TB meningitis. **High-Yield Clinical Pearls for NEET-PG:** * **BCG Vaccine:** Provides roughly 50% protection against Leprosy (highest protection seen in trials in Uganda). * **Strategy for Leprosy:** The current WHO strategy is "Towards Zero Leprosy," focusing on active case finding and Post-Exposure Prophylaxis (PEP) with a single dose of **Rifampicin**. * **Herd Immunity:** Not applicable to Tetanus (non-communicable) or Leprosy (low infectivity/long incubation).

Question 1

Which one of the following doses in Loeffler units of Diphtheria Toxoid is incorporated in DPT vaccine per dose?

Accepted Answer

25

Answer

5

Answer

15

Answer

35

Question 2

Which age group is targeted in the WHO's catch-up vaccination strategy for measles elimination?

Accepted Answer

9 months to 14 years

Answer

6 months to 5 years

Answer

9 months to 10 years

Answer

6 months to 10 years

Question 3

Regarding poliovirus responsible for poliomyelitis, all are true except:

Accepted Answer

Type 3 is most common in India

Answer

Type 1 is responsible for most epidemics

Answer

Type 1 is most common in India

Answer

Type 2 is eradicated worldwide

Question 4

Cervarix vaccine for HPV contains which strains of virus?

Accepted Answer

HPV 16, 18

Answer

HPV 6, 11

Answer

HPV 6, 11, 16, 18

Answer

HPV 16, 18, 31, 33

Question 5

Reverse cold chain is used for which of the following purposes?

Accepted Answer

Carrying stool samples of polio patients from a PHC to the lab

Answer

Transporting outdated vaccines from PHC to a district hospital

Answer

Transporting vaccine to a lab to check its potency

Answer

Transporting vaccine from a camp to a sub-centre

Question 6

Active immunization following exposure is most commonly given for which of the following?

Accepted Answer

Rabies

Answer

Polio

Answer

Plague

Answer

Measles

Question 7

Which of the following vaccines is MOST sensitive to heat?

Accepted Answer

OPV

Answer

Measles

Answer

BCG

Answer

IPV

Question 8

The 17D vaccine is used for the prevention and control of which disease?

Accepted Answer

Yellow fever

Answer

Japanese encephalitis

Answer

Hemorrhagic fever

Answer

Dengue

Question 9

Mass immunization is indicated in all of the following conditions, except?

Accepted Answer

Leprosy

Answer

Cholera

Answer

Influenza

Answer

Tuberculosis

Question 10

Post-exposure prophylaxis is indicated in all of the following conditions EXCEPT?

Accepted Answer

Typhoid

Answer

Rabies

Answer

Chickenpox

Answer

Measles

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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