Immunization and Vaccine-Preventable Diseases Practice Questions

Q: Which of the following vaccines should not be kept in a freezer?

DPT. **Explanation:** The correct answer is **A. DPT**. **1. Why DPT is the correct answer:** DPT is an **adsorbed vaccine** that contains aluminum salts (aluminum hydroxide or phosphate) as an adjuvant to enhance the immune response. If these vaccines are frozen, the aluminum salts crystallize and precipitate, leading to the irreversible loss of potency and an increased risk of local reactions (like sterile abscesses) upon injection. Therefore, DPT must be stored in the **refrigerator (2°C to 8°C)** and never in the freezer. Other freeze-sensitive vaccines include TT, DT, Hepatitis B, Pentavalent, and PCV. **2. Why other options are incorrect:** * **B. Measles:** This is a live-attenuated lyophilized (freeze-dried) vaccine. It is relatively heat-stable in its powder form and is not damaged by freezing. In fact, at the district level and above, it is often stored in sub-zero temperatures. * **C. OPV (Oral Polio Vaccine):** This is the **most heat-sensitive** vaccine in the immunization program. To maintain its potency, it must be stored at **-20°C** for long-term storage. Freezing does not damage OPV; it preserves it. **3. High-Yield Clinical Pearls for NEET-PG:** * **Shake Test:** This is a specific test used to determine if an adsorbed vaccine (like DPT or TT) has been damaged by freezing. If the vaccine appears cloudy or has sediments that settle quickly after shaking, it has failed the test and must be discarded. * **Heat Sensitivity Order:** Most sensitive → Least sensitive: **OPV > Measles > BCG > DPT > DT > TT.** * **Storage:** In a standard ILR (Ice-Lined Refrigerator), freeze-sensitive vaccines (DPT, Hep B) are kept at the **top**, while heat-sensitive vaccines (OPV, Measles) are kept at the **bottom** (the coolest part).

Q: Vaccine and immunoglobulin can be given together in all conditions except:

Measles. ### Explanation The core principle behind this question is the **interference between pre-formed antibodies (immunoglobulins) and live-attenuated vaccines.** **Why Measles is the correct answer:** Measles vaccine is a **live-attenuated vaccine**. If measles immunoglobulin is administered simultaneously with the vaccine, the pre-formed antibodies will neutralize the live virus particles before they can replicate sufficiently to trigger an active immune response. This renders the vaccine ineffective. According to standard guidelines, if immunoglobulin is given, one must wait at least **3 to 11 months** (depending on the dose) before administering the Measles/MMR vaccine. **Why the other options are incorrect:** In cases of **Tetanus, Rabies, and Hepatitis B (HBV)**, the goal is to provide **Passive-Active Immunity**. * **Rabies & Tetanus:** These are life-threatening conditions where immediate protection (Passive) is required via RIG/TIG, while the body simultaneously starts producing its own antibodies (Active) via the vaccine. * **HBV:** Post-exposure prophylaxis (e.g., needle-stick injury or birth to an HBsAg+ mother) requires both HBIG and the Hep B vaccine for immediate and long-term coverage. * **Key Rule:** In these cases, the vaccine and immunoglobulin must be administered at **different anatomical sites** using different syringes to prevent physical neutralization. **High-Yield Clinical Pearls for NEET-PG:** * **Live Vaccines vs. IG:** Always maintain a gap. If a live vaccine is given first, wait 2 weeks before giving IG. If IG is given first, wait at least 3 months before giving a live vaccine. * **Exception:** The **Yellow Fever** vaccine is generally not affected by IG. * **Oral Live Vaccines:** Oral Polio Vaccine (OPV) and Rotavirus are not affected by systemic IG and can be given simultaneously. * **Passive-Active Immunity** is the standard of care for post-exposure prophylaxis in Rabies, Tetanus, HBV, and Varicella.

Q: At what age is the Rubella vaccine typically administered?

1 to 14 years. **Explanation:** The primary objective of Rubella vaccination in public health is to prevent **Congenital Rubella Syndrome (CRS)**. While Rubella is a mild viral illness in children, infection during early pregnancy can lead to devastating fetal complications, including cataracts, deafness, and cardiac defects. **Why Option A is correct:** Under the Universal Immunization Programme (UIP) in India, the **Measles-Rubella (MR) campaign** specifically targets children aged **9 months to 15 years** (effectively the 1–14 years age group). By vaccinating this cohort, the health system aims to build "herd immunity" and eliminate the virus from the community, thereby protecting pregnant women from exposure. In the routine schedule, the MR vaccine is given in two doses: the first at 9–12 months and the second at 16–24 months. **Why other options are incorrect:** * **Option B ( 50 years):** Rubella is primarily a childhood disease. By age 50, most individuals have either acquired natural immunity or are well past reproductive age, making vaccination at this stage irrelevant for preventing CRS. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Type:** Live attenuated (RA 27/3 strain is most commonly used). * **Contraindication:** Pregnancy. Women should be advised to avoid pregnancy for **1 month** (previously 3 months) after receiving the vaccine. * **CRS Triad (Gregg’s Triad):** Cataract, Sensorineural hearing loss, and Congenital heart disease (Patent Ductus Arteriosus). * **Diagnostic Marker:** Presence of Rubella-specific IgM antibodies in a newborn is diagnostic of CRS.

Q: Which of the following is a serogroup included in the meningococcal vaccine?

ACWY. ### Explanation **Correct Option: A (ACWY)** **Medical Concept:** *Neisseria meningitidis* is classified into serogroups based on the composition of its capsular polysaccharide. While there are 12 serogroups, most invasive meningococcal diseases globally are caused by six: **A, B, C, W-135, X, and Y**. The standard quadrivalent meningococcal vaccines (both Polysaccharide and Conjugate types) are designed to target the four most prevalent serogroups: **A, C, W-135, and Y**. These vaccines provide broad protection against epidemic and endemic meningitis in various geographical regions, including the "Meningitis Belt" of sub-Saharan Africa and during the Hajj pilgrimage. **Analysis of Incorrect Options:** * **Options B, C, and D:** These are incorrect combinations. While **Serogroup B** is a major cause of disease (especially in developed nations), it is traditionally excluded from the quadrivalent (ACWY) vaccine. This is because the Serogroup B polysaccharide is poorly immunogenic (it mimics human neural cell adhesion molecules). Protection against Serogroup B requires a separate, protein-based vaccine (e.g., Bexsero or Trumenba), rather than the standard polysaccharide/conjugate ACWY formulation. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Types:** Available as **MPSV4** (Polysaccharide) and **MenACWY** (Conjugate). The conjugate vaccine is preferred due to longer-lasting immunity and herd protection. * **Hajj Requirement:** Proof of vaccination with the quadrivalent ACWY vaccine is a mandatory visa requirement for pilgrims traveling to Saudi Arabia. * **Target Population:** High-risk groups include individuals with terminal complement deficiency, functional or anatomic asplenia, and laboratory personnel. * **Serogroup A:** Historically the most common cause of epidemics in Africa and Asia.

Q: A 1-year-old child who received BCG at birth and OPV is due for vaccination. Which of the following vaccines should be administered?

Measles, DPT, OPV, Hib, Hepatitis B. ### Explanation **1. Why Option B is Correct:** According to the **National Immunization Schedule (NIS)** in India, a child who has only received BCG and OPV at birth is significantly delayed. At 1 year of age, the child must receive the "catch-up" doses for all primary vaccines missed during the first year. * **Pentavalent Vaccine (DPT + Hib + Hep B):** The child needs protection against Diphtheria, Pertussis, Tetanus, *Haemophilus influenzae* type b, and Hepatitis B. * **OPV:** Subsequent doses of Oral Polio Vaccine are required to build mucosal immunity. * **Measles (MR):** The first dose is typically given at 9 completed months. Since the child is now 1 year old, this is a priority to prevent outbreaks. **2. Why Other Options are Incorrect:** * **Option A:** BCG is already administered at birth. Repeating it is unnecessary unless there is no scar and the child is <1 year (though current guidelines focus on birth dose). It misses DPT and Measles. * **Option C & D:** These options omit **Measles**, which is a critical vaccine administered at 9 months. Failure to include Measles leaves the child vulnerable to one of the most common causes of vaccine-preventable childhood mortality. **3. NEET-PG High-Yield Pearls:** * **Pentavalent Vaccine:** Replaces individual DPT, Hep B, and Hib shots. It is given at 6, 10, and 14 weeks. * **Measles/MR Vaccine:** Minimum age is 9 months. If missed, it can be given up to 5 years of age. * **BCG:** Can be given up to 1 year of age if missed at birth. * **Vitamin A:** The first dose (1 lakh IU) is always administered alongside the 1st dose of Measles/MR. * **Catch-up Rule:** For a "left-out" child, always prioritize the primary series (DPT, OPV, Hep B, Measles) to ensure basic immunity.

Q: Isolation is not indicated for measles because which of the following is true?

Incubatory carriers are present.. **Explanation:** The primary reason isolation is ineffective for measles is the presence of **incubatory carriers**. In measles, the period of maximum infectivity occurs during the **prodromal stage** (the 3-4 days before the rash appears), characterized by coryza, cough, and fever. By the time the characteristic rash appears and a clinical diagnosis is made, the patient has already been shedding the virus for several days, infecting susceptible contacts. Therefore, isolating the patient after the rash appears is "locking the stable door after the horse has bolted." **Analysis of Options:** * **A & B (Healthy and Convalescent Carriers):** These are **incorrect** because measles does not have a chronic or healthy carrier state. The virus is eliminated from the body after the acute phase; you are either acutely ill or immune. * **C (Low Infectivity):** This is **incorrect**. Measles is one of the most highly infectious diseases known, with a Secondary Attack Rate (SAR) exceeding 90% in susceptible populations. **High-Yield Facts for NEET-PG:** * **Infectivity Period:** 4 days before to 5 days after the appearance of the rash. * **Koplik’s Spots:** Pathognomonic feature occurring in the pre-eruptive stage (opposite the lower 2nd molar). * **Secondary Attack Rate (SAR):** >90% (highest among vaccine-preventable diseases). * **Isolation:** While not effective for community control, "source reduction" (early diagnosis and notification) remains a standard public health measure.

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.

Question 1

Which of the following vaccines should not be kept in a freezer?

Accepted Answer

DPT

Answer

Measles

Answer

OPV

Answer

All of the above

Question 2

Which of the following is FALSE regarding pre-exposure tetanus immunization?

Accepted Answer

Tetanus immunoglobulin is injected to the mother.

Answer

If already immunized, a booster in the last trimester is advocated.

Answer

The vaccine is given intramuscularly.

Answer

Two doses are recommended.

Question 3

Which of the following is NOT a guideline for immunization against infectious diseases?

Accepted Answer

Hay fever, sickle cell anemia, and tuberculosis are contraindications for vaccination.

Answer

Live vaccines are contraindicated in pregnant women.

Answer

Live vaccines should not be administered within 3 months of giving human immunoglobulin.

Answer

Inactivated vaccines should not be given if there has been a significant reaction to a previous dose.

Question 4

A child was immunized at 6 months of age due to an epidemic of measles. What is the next recommended step for immunization?

Accepted Answer

Administer the vaccine as soon as the child completes 9 months of age.

Answer

Administer the vaccine after 4 weeks.

Answer

Administer the vaccine along with DPT.

Answer

No further action is needed.

Question 5

Vaccine and immunoglobulin can be given together in all conditions except:

Accepted Answer

Measles

Answer

Tetanus

Answer

Rabies

Answer

HBV

Question 6

At what age is the Rubella vaccine typically administered?

Accepted Answer

1 to 14 years

Answer

Less than 5 years

Answer

Greater than 50 years

Answer

None of the above

Question 7

Which of the following is a serogroup included in the meningococcal vaccine?

Accepted Answer

ACWY

Answer

ABCW

Answer

CYW

Answer

ABCY

Question 8

A 1-year-old child who received BCG at birth and OPV is due for vaccination. Which of the following vaccines should be administered?

Accepted Answer

Measles, DPT, OPV, Hib, Hepatitis B

Answer

BCG, OPV, Hepatitis B

Answer

DPT, OPV, Hib, Hepatitis B

Answer

DPT, OPV, Hepatitis B

Question 9

Isolation is not indicated for measles because which of the following is true?

Accepted Answer

Incubatory carriers are present.

Answer

Healthy carriers are common.

Answer

Carriers are typically convalescents.

Answer

Infectivity in diseased individuals is low.

Question 10

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

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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