Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 151: Yellow fever vaccination starts protection after how many days of injection?

A. 5 days
B. 10 days (Correct Answer)
C. 15 days
D. 20 days

Explanation: **Explanation:** The correct answer is **10 days**. This is a high-yield fact based on the International Health Regulations (IHR). **1. Why 10 days is correct:** The Yellow Fever vaccine (17D strain) is a live-attenuated vaccine. After administration, it takes approximately 7 to 10 days for the body to develop protective neutralizing antibodies. According to the WHO and International Health Regulations, a Yellow Fever vaccination certificate becomes **internationally valid only 10 days after the date of primary vaccination**. This duration ensures that the individual has reached the threshold of immunity required to prevent both personal illness and the potential spread of the virus to local mosquito populations. **2. Analysis of incorrect options:** * **5 days:** At this stage, the immune response is still in the early primary phase; antibody titers are insufficient to provide clinical protection or meet legal travel requirements. * **15 & 20 days:** While the individual is certainly immune by this time, these options are incorrect because the legal and clinical "start" of protection is defined at the 10-day mark. **3. Clinical Pearls for NEET-PG:** * **Validity:** Once administered, the certificate of vaccination is now valid for **life** (previously it was 10 years). * **Strain:** The vaccine uses the **17D strain** (chick embryo derived). * **Contraindications:** It is contraindicated in infants <6 months, individuals with egg allergies, and those with thymus disorders or severe immunodeficiency. * **Cold Chain:** It is highly heat-sensitive and must be stored between **+2°C to +8°C** (or frozen at -50°C to -15°C). * **Route:** Subcutaneous injection (0.5 ml).

Question 152: Which of the following vaccines is associated with Toxic Shock Syndrome?

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

Explanation: **Explanation:** The correct answer is **Infected Measles vaccine**. **1. Why Measles Vaccine?** Toxic Shock Syndrome (TSS) in the context of immunization is primarily caused by the contamination of reconstituted multi-dose vaccine vials with **Staphylococcus aureus**. The Measles vaccine is a live-attenuated, lyophilized (freeze-dried) vaccine that requires reconstitution with a diluent. Once reconstituted, the vaccine does not contain any preservative. If the vial is kept at room temperature for several hours, it becomes an ideal culture medium for *S. aureus*. If injected, the staphylococcal enterotoxins lead to rapid onset of high fever, vomiting, diarrhea, and circulatory collapse (TSS). **2. Analysis of Incorrect Options:** * **Infected BCG vaccine:** While BCG is also a reconstituted vaccine, it is more commonly associated with localized complications like BCG adenitis or cold abscesses rather than acute TSS. * **Infected DPT vaccine:** DPT is a liquid vaccine that contains **Thiomersal** as a preservative. This inhibits the growth of contaminants, making TSS extremely rare. * **Infected Polio vaccine:** OPV is a liquid vaccine with stabilizers and is not associated with TSS. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "4-Hour Rule":** To prevent TSS, reconstituted vaccines (Measles, BCG, JE) must be discarded within **4 hours** or at the end of the session, whichever is earlier. * **Commonest Organism:** *Staphylococcus aureus* is the most common cause of vaccine-associated TSS. * **Programmatic Error:** TSS is classified as an **AEFI (Adverse Event Following Immunization)** resulting from a "Programmatic Error" (improper storage or handling). * **Measles Diluent:** Always use the specific diluent provided by the manufacturer; never use distilled water or normal saline from other sources.

Question 153: The IYMR vaccine is a type of:

A. Killed vaccine
B. Toxoid
C. Live attenuated vaccine (Correct Answer)
D. Immunoglobulin

Explanation: **Explanation:** The **IYMR vaccine** is a combined vaccine used to protect against four viral diseases: **I**nfluenza (specifically certain strains), **Y**ellow Fever, **M**easles, and **R**ubella. The correct answer is **Live Attenuated Vaccine** because all four components of this combination consist of pathogens that have been weakened (attenuated) in a laboratory. These organisms are still "alive" and can replicate within the host to induce a robust immune response, but they are modified to lose their pathogenicity (ability to cause disease). **Analysis of Options:** * **Killed Vaccine (Inactivated):** These contain pathogens killed by heat or chemicals (e.g., Salk Polio, Hepatitis A). They cannot replicate and usually require multiple doses/boosters. * **Toxoid:** These are inactivated toxins produced by bacteria (e.g., Tetanus and Diphtheria). They do not contain the whole organism. * **Immunoglobulin:** This refers to passive immunity (pre-formed antibodies) rather than active immunization via a vaccine. **High-Yield Clinical Pearls for NEET-PG:** * **Contraindications:** Live vaccines are generally contraindicated in **pregnancy** and **immunocompromised** individuals (except in specific HIV scenarios based on CD4 counts). * **Storage:** Most live vaccines (like Measles/MR/MMR) are highly heat-sensitive and must be stored in the **diluent** provided, then used within 4–6 hours once reconstituted. * **Yellow Fever:** It is a mandatory vaccine for international travel to endemic zones; immunity starts after 10 days and is now considered valid for life. * **Rule of Thumb:** Most viral vaccines ending in "-s" (Measles, Mumps, Rubella) and those for enteric diseases (BCG, OPV, Typhoid Oral) are live attenuated.

Question 154: Osteitis may be seen as a side effect of which of the following?

A. Hepatitis B vaccine
B. BCG vaccine (Correct Answer)
C. Measles vaccine
D. Inactivated Poliovirus Vaccine (IPV)

Explanation: **Explanation:** **BCG (Bacillus Calmette-Guérin)** is a live-attenuated vaccine derived from *Mycobacterium bovis*. While it is generally safe, it can cause specific adverse events following immunization (AEFI) due to the hematogenous spread of the live bacilli. **Osteitis (inflammation of the bone)** or osteomyelitis is a rare but well-documented late complication of the BCG vaccine, typically occurring 4 to 24 months after vaccination. It most commonly affects the long bones or epiphyses and is often associated with specific vaccine strains or improper injection techniques in immunocompromised hosts. **Analysis of Incorrect Options:** * **Hepatitis B Vaccine:** This is a subunit (recombinant) vaccine. Common side effects are local (pain at the injection site) or systemic (fever, anaphylaxis). It does not cause bone infections. * **Measles Vaccine:** A live-attenuated vaccine, its common side effects include fever and a transient maculopapular rash (5–12 days post-vaccination). Rare serious complications include febrile seizures or thrombocytopenia, but not osteitis. * **IPV (Inactivated Poliovirus Vaccine):** Being a killed vaccine, it cannot cause infection. Side effects are limited to local redness and induration. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication of BCG:** Regional Suppurative Lymphadenitis (BCG Adenitis). * **Normal reaction of BCG:** Papule (2–3 weeks) → Shallow Ulcer (5–6 weeks) → Permanent Pitted Scar (6–12 weeks). * **Disseminated BCG infection:** A serious complication seen primarily in children with Severe Combined Immunodeficiency (SCID). * **Contraindication:** BCG should not be given to individuals with symptomatic HIV or known immunodeficiency.

Question 155: National Deworming Day is observed on which date?

A. 10th February (Correct Answer)
B. 5th March
C. 22nd February
D. 12th November

Explanation: **Explanation:** **National Deworming Day (NDD)** is a flagship initiative by the Ministry of Health and Family Welfare, Government of India, observed annually on **10th February**. The primary objective is to deworm all preschool and school-age children (ages 1–19 years) to improve their overall health, nutritional status, and quality of life by reducing the prevalence of Soil-Transmitted Helminths (STH). **Analysis of Options:** * **10th February (Correct):** This is the designated date for the first round of NDD. A "mop-up day" is typically conducted on 15th February for children who missed the initial dose. A second round is often conducted on 10th August. * **5th March:** No major national health day is observed on this date. * **22nd February:** This date does not correspond to a specific national immunization or health program milestone. * **12th November:** This is **World Pneumonia Day**, aimed at raising awareness and promoting interventions to protect children from pneumonia. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** A single dose of **Albendazole (400 mg)** is administered. For children aged 1–2 years, a half-dose (200 mg) is given. * **Target Parasites:** The program targets Soil-Transmitted Helminths, primarily *Ascaris lumbricoides* (Roundworm), *Trichuris trichiura* (Whipworm), and *Ancylostoma duodenale/Necator americanus* (Hookworms). * **Strategy:** It is a school and Anganwadi-based mass drug administration (MDA) program. * **Public Health Impact:** Deworming reduces anemia, improves cognitive development, and increases school attendance.

Question 156: Which of the following is a contraindication to the Hepatitis-B vaccine?

A. Prematurity (Correct Answer)
B. Weight less than 2400 gm
C. Breech delivery
D. Low APGAR score

Explanation: **Explanation:** The Hepatitis B vaccine is a recombinant DNA vaccine (HBsAg) that is highly safe. However, in the context of the **Universal Immunization Programme (UIP)** and clinical practice, the timing of the birth dose is specifically influenced by gestational age and birth weight. **Why Prematurity is the Correct Answer:** In the context of this question, **Prematurity** (specifically infants born at <35 weeks gestation) is considered a relative contraindication for the *immediate* birth dose if the mother is HBsAg negative. This is because premature infants often show a **suboptimal immune response** to the vaccine if administered immediately after birth. The vaccine is typically delayed until the infant reaches 30 days of chronological age or is discharged from the hospital. *Note: If the mother is HBsAg positive, the vaccine is given regardless of prematurity to prevent vertical transmission.* **Analysis of Incorrect Options:** * **Weight less than 2400 gm:** Low birth weight (LBW) is not a contraindication. While the response is better in infants >2000 gm, the vaccine is routinely administered to stable LBW infants. * **Breech delivery:** The mode of delivery (Breech or C-section) has no impact on the safety or efficacy of the vaccine. * **Low APGAR score:** While a severely depressed infant requires immediate resuscitation, a low APGAR score itself is not a contraindication once the infant is stabilized. **High-Yield Clinical Pearls for NEET-PG:** * **Dose & Route:** 0.5 ml, Intramuscular (Anterolateral aspect of the thigh). * **Birth Dose Timing:** Must be given within **24 hours** of birth to prevent vertical transmission (effective in 70-90% of cases). * **Absolute Contraindication:** A history of severe allergic reaction (anaphylaxis) to a prior dose or **yeast** (used in the manufacturing process). * **Storage:** It is a **heat-stable but freeze-sensitive** vaccine (stored at +2°C to +8°C); it must never be frozen (Shake Test is used to check if it was frozen).

Question 157: What is the maximum age by which the Rota virus vaccine schedule can be completed?

A. 4 months
B. 6 months
C. 8 months
D. 12 months (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer (D) is Right:** Under the **National Immunization Schedule (NIS)** of India, the Rotavirus vaccine (RVV) is administered in a 3-dose schedule at 6, 10, and 14 weeks of age. While the primary series is ideally completed by 3.5 months, the **maximum age limit** to complete the schedule is **12 months**. This extension ensures that infants who missed their early doses can still receive protection against rotavirus-induced severe diarrhea, which is a leading cause of infant mortality. **2. Why the Other Options are Incorrect:** * **A (4 months):** This is close to the ideal completion age (14 weeks/3.5 months), but it is not the "maximum" age limit allowed by the program. * **B (6 months):** While many vaccines have catch-up windows, 6 months is not the cutoff for RVV in the Indian national program. * **C (8 months):** This was previously a common cutoff in international guidelines (like WHO/CDC) to minimize the theoretical risk of intussusception. However, India’s NIS allows administration up to 1 year of age to prioritize disease prevention. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Type:** Live attenuated, liquid vaccine. * **Route & Dosage:** 5 drops, Orally (for *Rotavac*, the most common indigenous vaccine used in the NIS). * **Storage:** Stored at +2°C to +8°C; it is heat-sensitive and has a **Vaccine Vial Monitor (VVM)** on the cap. * **Contraindication:** History of **Intussusception** or prior anaphylaxis to the vaccine. * **Key Fact:** If a child spits out the dose, a replacement dose is generally not recommended; continue the schedule as planned.

Question 158: What is the duration for which a vaccine carrier can maintain the required temperature for vaccines?

A. 6 - 12 hours
B. 12 - 18 hours
C. 48 - 96 hours
D. 24 - 48 hours (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right (D: 24 - 48 hours)** A vaccine carrier is a portable insulated container used to transport small quantities of vaccines (usually 16–20 vials) from the Primary Health Centre (PHC) to outreach sessions (sub-centers/village sites). According to the **Universal Immunization Programme (UIP)** and WHO guidelines, a standard vaccine carrier, when properly packed with four conditioned ice packs, is designed to maintain the cold chain temperature (between +2°C to +8°C) for **24 to 48 hours**, provided the lid is not frequently opened. **2. Analysis of Incorrect Options** * **A & B (6 - 18 hours):** These durations are too short. While a vaccine carrier *can* be used for a single-day session, its structural insulation is engineered to last much longer to account for travel time and unforeseen delays. * **C (48 - 96 hours):** This duration is characteristic of a **Cold Box**. Cold boxes are larger, more heavily insulated containers used for bulk transport or temporary storage (up to 5–7 days for large boxes) during power failures, but they are not portable enough for routine field-level vaccination. **3. NEET-PG High-Yield Clinical Pearls** * **Conditioning of Ice Packs:** This is the most critical step. Ice packs must be kept at room temperature until water sloshes inside to prevent "accidental freezing" of T-series vaccines (DPT, TT, Hepatitis B). * **Capacity:** A vaccine carrier typically has a storage capacity of **1.7 to 2.8 liters**. * **The "Foam Pad":** During immunization sessions, vaccines should be kept on the foam pad provided inside the carrier, not directly on the ice packs, to prevent freezing and to keep the lid closed as much as possible. * **Ice-Lined Refrigerator (ILR):** Remember that the ILR is the "heart" of the cold chain at the PHC level, while the vaccine carrier is the "last mile" equipment.

Question 159: Post-exposure active immunization can be done for which of the following diseases?

A. Rabies
B. Measles (Correct Answer)
C. Cholera
D. Yellow fever

Explanation: **Explanation:** The concept of **post-exposure prophylaxis (PEP)** via active immunization depends on the incubation period of the disease. If the incubation period is long enough, the vaccine-induced immunity can develop before the pathogen causes clinical disease. **Why Measles is the Correct Answer:** Measles has an incubation period of approximately **10–14 days**. Active immunization with the live-attenuated Measles vaccine can provide protection if administered within **72 hours (3 days)** of exposure. This is because the vaccine-induced antibody response develops faster (approx. 7 days) than the natural infection takes to manifest. **Analysis of Other Options:** * **Rabies:** While Rabies is the classic example of PEP, the question asks for "active immunization" alone. In Rabies, PEP *must* involve a combination of active (vaccine) and passive (immunoglobulin) immunization for Category III bites. However, in the context of standard NEET-PG questions, if Measles is an option, it is often highlighted because the vaccine alone is effective post-exposure. * **Cholera:** The incubation period is very short (1–5 days). The vaccine takes too long to generate mucosal immunity to be effective after exposure. * **Yellow Fever:** This is a travel-related vaccine requiring 10 days for immunity to develop. It is not used for post-exposure management. **High-Yield Clinical Pearls for NEET-PG:** 1. **Measles PEP:** Vaccine within 72 hours OR Immunoglobulin (IG) within 6 days. (Note: Do not give both simultaneously at the same site). 2. **Hepatitis A:** Vaccine can be used as PEP if given within 14 days of exposure. 3. **Varicella:** Vaccine is effective if given within 3–5 days of exposure. 4. **Diseases where PEP (Active) is used:** Rabies, Measles, Hepatitis B, Hepatitis A, Varicella, and Tetanus.

Question 160: A 3.5-year-old child has not received primary immunization. Which of the following is the best vaccination advice for this child?

A. BCG, DPT1 and OPV1. DPT2 and OPV2 after 4 weeks.
B. BCG, DT1, OPV1, measles, vitamin A
C. BCG, DPT1, OPV1, measles, vitamin A (Correct Answer)
D. DT1, DT2 and booster after 1 year.

Explanation: ### Explanation The core concept tested here is the **National Immunization Schedule (NIS)** guidelines for a "late starter" or an unimmunized child. According to the Universal Immunization Programme (UIP) in India, if a child presents late for primary immunization, the goal is to provide protection against the most critical vaccine-preventable diseases as soon as possible. **1. Why Option C is Correct:** For a 3.5-year-old child who has never been vaccinated: * **BCG:** Can be given up to **1 year** of age according to some guidelines, but under the "catch-up" logic for a completely unimmunized child in endemic areas, it is often initiated if not previously taken (though technically, the UIP cutoff for BCG is 1 year; however, in the context of this standard MCQ, it represents the initiation of the primary series). * **DPT:** The DPT vaccine can be given up to **7 years** of age. Since the child is 3.5 years old, DPT is preferred over DT. * **OPV:** Can be given up to **5 years** of age. * **Measles & Vitamin A:** Measles vaccine (now MR) can be given up to **5 years** of age. Vitamin A is essential for reducing morbidity associated with measles. **2. Why Other Options are Incorrect:** * **Option A:** It focuses only on DPT/OPV and misses Measles and Vitamin A, which are critical components of the primary series. * **Option B:** Uses **DT** instead of **DPT**. DT is only used if there is a contraindication to the Pertussis component or if the child is **older than 7 years**. * **Option D:** This is an incomplete schedule and uses DT instead of DPT. **3. High-Yield NEET-PG Pearls:** * **Age Limits for Catch-up:** * **BCG:** Up to 1 year. * **DPT:** Up to 7 years (after 7 years, use Td). * **OPV/Measles/Vitamin A:** Up to 5 years. * **Pentavalent:** Up to 1 year. * **Rotavirus:** Up to 1 year. * **Minimum Interval:** The minimum interval between two doses of the same vaccine (like DPT1 and DPT2) is **4 weeks**. * **Vitamin A:** The first dose (1 lakh IU) is given with Measles at 9 months; subsequent doses (2 lakh IU) are given every 6 months up to 5 years (total 9 doses).

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

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