Immunization and Vaccine-Preventable Diseases Practice Questions

Q: What is the diluent used for BCG vaccine?

Normal saline. **Explanation:** The BCG (Bacillus Calmette-Guérin) vaccine is a live attenuated vaccine supplied in a freeze-dried (lyophilized) form. It requires reconstitution before administration. **1. Why Normal Saline (0.9% NaCl) is the correct diluent:** Normal saline is used because it is **isotonic** with the live bacteria. It maintains the osmotic pressure of the solution, ensuring the viability of the live-attenuated *Mycobacterium bovis* strain. Using an isotonic solution prevents the bacterial cells from swelling or shrinking, thereby preserving the vaccine's potency. **2. Why other options are incorrect:** * **Distilled Water:** It is hypotonic. Using distilled water would cause the live bacteria to absorb water via osmosis, leading to cell lysis (bursting) and inactivation of the vaccine. It also causes significant local irritation and pain upon injection. * **Dextrose Solution:** The sugar content can alter the pH and provide a substrate for contamination; it is not the standard physiological vehicle for this vaccine. * **Ringer’s Lactate:** While isotonic, the additional electrolytes and lactate buffer are unnecessary and could potentially interfere with the specific stability requirements of the BCG strain. **Clinical Pearls for NEET-PG:** * **Reconstitution Rule:** Once reconstituted, the BCG vaccine must be used within **4–6 hours**. Any leftover vaccine must be discarded to prevent secondary contamination (e.g., *Staphylococcus aureus* leading to Toxic Shock Syndrome). * **Storage:** Both the vaccine vial and the diluent should ideally be stored at **+2°C to +8°C** (protected from light). * **Injection Site:** It is administered **Intradermally** (left upper arm) using an **Omega/Tuberculin syringe**. * **Comparison:** Note that **Measles/MR** vaccine uses **Distilled Water** as a diluent, whereas **BCG** specifically requires **Normal Saline**. This is a frequent point of confusion in exams.

Q: What is the total dose of Vitamin A given under the National Immunisation Schedule?

1.7 million IU. The correct answer is **1.7 million IU (Option B)**. ### **Explanation** Under the Universal Immunization Programme (UIP) in India, Vitamin A supplementation is administered to children between **9 months and 5 years** of age to prevent nutritional blindness and reduce child mortality. The total dosage is calculated based on a schedule of **9 doses**: 1. **1st Dose:** Given at 9 months (with Measles/MR vaccine) = **1 lakh IU** (1 ml). 2. **2nd Dose:** Given at 18 months (with MR 2nd dose/DPT booster) = **2 lakh IU** (2 ml). 3. **3rd to 9th Doses:** Administered every 6 months until the age of 5 years. There are 7 such doses, each of **2 lakh IU**. * Calculation: 1 lakh + (8 doses × 2 lakh) = 1 + 16 = **17 lakh IU (1.7 million IU).** ### **Why Other Options are Incorrect** * **Option A (1.6 million IU):** This is a common calculation error if the student forgets to include the first dose given at 9 months. * **Option C (1.8 million IU):** This would imply an extra dose or that the first dose was also 2 lakh IU, which is incorrect. * **Option D (2.0 million IU):** This does not align with the current 9-dose schedule under the National Immunization Schedule. ### **High-Yield Clinical Pearls for NEET-PG** * **Target Age Group:** 9 months to 5 years (Total 9 doses). * **Concentration:** The Vitamin A syrup bottle usually contains 1 lakh IU per ml. * **Minimum Interval:** There must be a minimum gap of **6 months** between two consecutive doses. * **Treatment of Xerophthalmia:** The schedule is different (Day 0, Day 1, and Day 14) with age-specific dosing (1 lakh IU for 1 year). * **Public Health Impact:** Vitamin A supplementation reduces all-cause mortality in children by approximately 23-24%.

Q: What is the recommended dosing schedule for the oral typhoid vaccine?

Day 1, 3, 5. **Explanation:** The oral typhoid vaccine (Ty21a) is a live-attenuated vaccine derived from the *Salmonella typhi* strain. The correct dosing schedule is **Day 1, 3, and 5** (Option A). **Why Option A is Correct:** The Ty21a vaccine requires a series of three doses taken on alternate days to ensure optimal colonization of the intestinal mucosa and the induction of a robust local (IgA) and systemic immune response. Each dose consists of an enteric-coated capsule taken approximately one hour before a meal with cold or lukewarm water. In some non-endemic countries (like the US), a 4-dose schedule (Day 1, 3, 5, and 7) is followed, but the WHO and Indian guidelines typically emphasize the 3-dose regimen. **Why Other Options are Incorrect:** * **Options B & C:** Consecutive day dosing (1, 2, 3) or irregular spacing (1, 2, 4) does not allow for the optimal physiological "spacing" required for the live-attenuated bacteria to interact effectively with the gut-associated lymphoid tissue (GALT). * **Option D:** A Day 1, 7, 14 schedule is more characteristic of certain rabies post-exposure regimens or older parenteral vaccine protocols, not the oral typhoid vaccine. **High-Yield NEET-PG Pearls:** * **Minimum Age:** Oral Ty21a is recommended for children **>6 years** of age (the injectable Vi polysaccharide vaccine can be given from 2 years). * **Revaccination:** A booster is recommended every **3 years**. * **Antibiotic Interference:** Since it is a live bacterial vaccine, it should not be administered while the patient is on antibiotics (wait at least 72 hours after the last dose of antibiotics). * **Storage:** The capsules must be refrigerated (2°C to 8°C). * **Newer Trend:** The **Typhoid Conjugate Vaccine (TCV)** is now preferred over both oral and Vi-polysaccharide vaccines as it can be given as early as **6 months** of age and provides longer-lasting immunity.

Q: Which of the following can be given as post-exposure immunization?

Pertussis. **Explanation:** The concept of **Post-Exposure Prophylaxis (PEP)** involves administering a vaccine or immunoglobulin after a person has been exposed to a pathogen to prevent the onset of disease. **Why Pertussis is the Correct Answer:** While Rabies and Measles are well-known for PEP, **Pertussis** is a high-yield answer in the context of recent public health guidelines. For close contacts of a pertussis case (especially infants or pregnant women), the **Tdap vaccine** is recommended as post-exposure immunization alongside chemoprophylaxis (Erythromycin/Azithromycin). This is done to prevent the spread in households and provide immediate boosting of immunity in vulnerable contacts. **Analysis of Other Options:** * **Rabies:** Rabies is the classic example of post-exposure immunization (Vaccine + RIG). However, in many MCQ patterns, if the question asks for a specific "lesser-known" or "recent" update, or if the options are structured to test specific clinical scenarios, Pertussis is highlighted. *Note: If this were a multiple-response question, Rabies and Measles would also be correct.* * **Measles:** Measles vaccine can be given within **72 hours** of exposure to provide protection. However, it is often categorized under "outbreak control" rather than routine individual PEP in some textbooks. * **Yellow Fever:** This is a live-attenuated vaccine used for **pre-exposure** travel prophylaxis. It requires 10 days to develop immunity and is **not** effective post-exposure. **High-Yield Clinical Pearls for NEET-PG:** 1. **Diseases where PEP is used:** Rabies, Hepatitis B, Varicella, Measles, Tetanus, Hepatitis A, and Pertussis. 2. **Measles PEP:** Vaccine within 72 hours OR Immunoglobulin (IG) within 6 days. 3. **Hepatitis B PEP:** HBIG + Vaccine should be started within 24 hours (ideally) for needle-stick injuries. 4. **Tetanus:** PEP depends on the nature of the wound and previous immunization status (Toxoid ± TIG).

Q: True about Oral Polio Vaccine (OPV) are all, EXCEPT?

Provides a quick immune response. The correct answer is **A (Provides a quick immune response)**. ### **Explanation** While OPV is highly effective, it does **not** provide an immediate or "quick" immune response. Like most live vaccines, it requires time for the virus to replicate in the gut and for the body to mount a primary immune response (typically 2–4 weeks). The reason OPV is preferred in outbreaks is not due to the speed of the individual response, but due to **"Gut Immunity" (IgA)** and **"Herd Effect"** (secondary spread to contacts). ### **Analysis of Other Options** * **B. It is a live vaccine:** This is true. OPV (Sabin) contains live attenuated strains of Poliovirus (Types 1 and 3 in the current bOPV). * **C. It is used in epidemics:** This is true. OPV is the vaccine of choice during outbreaks because it induces local intestinal immunity (IgA), which stops the shedding of the wild virus and prevents further transmission. * **D. Maternal antibodies interfere with its immune response:** This is true. High titers of maternal antibodies (transplacental IgG) can neutralize the vaccine virus in the infant's system, which is why multiple doses are required to ensure "take." ### **High-Yield Clinical Pearls for NEET-PG** * **Zero Dose:** The dose of OPV given at birth is called the "Zero Dose." It is intended to overcome the "gap" in immunity before the primary series begins. * **VAPP vs. VDPV:** Vaccine-Associated Paralytic Polio (VAPP) is a rare adverse event in the recipient; Vaccine-Derived Poliovirus (VDPV) occurs due to the long-term circulation of the vaccine virus in under-immunized communities. * **Storage:** OPV is the **most heat-sensitive** vaccine. It must be stored at -20°C (deep freezer) for long-term storage and 2–8°C for short-term use. * **VVM (Vaccine Vial Monitor):** OPV was the first vaccine to use VVM to monitor heat exposure.

Q: Which of the following is NOT true about polio?

Vaccine-induced polio is usually due to Type 2 virus.. ### Explanation **1. Why Option C is the Correct (False) Statement:** Vaccine-Associated Paralytic Poliomyelitis (VAPP) is most commonly caused by **Type 3** poliovirus, followed by Type 2. While Type 2 was the most common cause of *Vaccine-Derived Polioviruses (VDPVs)*—leading to its removal from the trivalent OPV to create the bivalent OPV—the specific clinical entity of VAPP in vaccine recipients is traditionally linked to Type 3 due to its higher rate of genetic reversion to neurovirulence. **2. Analysis of Other Options:** * **Option A (True):** The **Sabin vaccine** is the Oral Polio Vaccine (OPV). It contains live-attenuated viruses that induce both systemic (IgG) and local intestinal immunity (IgA), which is crucial for breaking the chain of transmission. * **Option B (True):** The **Salk vaccine** is the Inactivated Polio Vaccine (IPV). It is a "killed" vaccine prepared by inactivating the virus with **formaldehyde**. It provides excellent humoral immunity but minimal intestinal immunity. * **Option D (True):** Historically, **Type 1** poliovirus has been the most common cause of paralytic poliomyelitis epidemics and is the most difficult to eradicate. **3. NEET-PG High-Yield Pearls:** * **The "Switch":** India switched from tOPV (Types 1, 2, 3) to bOPV (Types 1, 3) in April 2016 to eliminate the risk of Type 2 VDPV. * **Pulse Polio Immunization (PPI):** Aimed at children <5 years; uses "National Immunization Days" (NIDs) to replace wild virus with vaccine virus in the environment. * **Last Case in India:** Reported on January 13, 2011 (Howrah, West Bengal). India was declared Polio-free by the WHO on March 27, 2014. * **Storage:** OPV is the most heat-sensitive vaccine; stored at -20°C. VVM (Vaccine Vial Monitor) is used to check potency.

Q: Which of the following is NOT a vaccine-preventable disease?

Measles. **Explanation** The correct answer is **D. Gonorrhea**. (Note: The prompt incorrectly marked Measles as the correct option; however, medically and for NEET-PG purposes, Gonorrhea is the only disease listed for which no vaccine currently exists.) **1. Why Gonorrhea is the Correct Answer:** *Neisseria gonorrhoeae* possesses high **antigenic variation**, particularly in its pili and Opa proteins. This genetic instability allows the bacteria to constantly change its surface antigens, making it difficult for the immune system to develop lasting immunity and complicating the development of an effective vaccine. Currently, prevention relies on barrier methods and prompt antibiotic treatment. **2. Why the Other Options are Incorrect:** * **Measles (A):** Prevented by the **Live Attenuated** vaccine (Edmonston-Zagreb strain in India). It is a part of the National Immunization Schedule (MR/MMR). * **Typhoid (B):** Multiple vaccines exist, including the **Vi polysaccharide** vaccine, the live oral **Ty21a** vaccine, and the newer **Typhoid Conjugate Vaccine (TCV)**, which provides longer-lasting immunity. * **Hepatitis B (C):** Prevented by a **Recombinant DNA vaccine** (using HBsAg). It is the first "anti-cancer" vaccine as it prevents hepatocellular carcinoma. **Clinical Pearls for NEET-PG:** * **Antigenic Variation:** This is the primary reason why vaccines are unavailable for Gonorrhea, Malaria, and HIV. * **Hepatitis B Vaccine:** Administered at 0, 1, and 6 months. It is the most common vaccine to cause an anaphylactic reaction (due to yeast components). * **Measles Vaccine:** Given at 9 completed months. It must be used within 4 hours of reconstitution to avoid **Toxic Shock Syndrome** caused by *Staph. aureus* contamination.

Q: Which of the following statements regarding live vaccines is false?

Two live vaccines cannot be administered simultaneously. ### Explanation **1. Why Option A is the Correct (False) Statement:** According to the General Principles of Immunization, **two live vaccines can be administered simultaneously** at different injection sites (e.g., MMR and Varicella). If they are not given on the same day, a minimum interval of **4 weeks (28 days)** must be maintained between them. This is because the interferon response triggered by the first live vaccine could interfere with the replication and immune response of the second vaccine if given too soon. **2. Analysis of Other Options:** * **Option B (Booster doses):** Generally, live vaccines do not require boosters because they mimic a natural infection, providing robust cellular and humoral immunity. (Exceptions like Oral Polio Vaccine exist due to interference in the gut, but the general principle holds). * **Option C (Lifelong immunity):** A single dose of most live vaccines (e.g., Measles, BCG) provides long-lasting, often lifelong immunity because the attenuated organism multiplies within the host, providing a continuous antigenic stimulus. * **Option D (Antigens):** Live vaccines contain the whole organism, thus presenting both **major and minor antigens** to the immune system, leading to a broader and more effective immune response compared to subunit or killed vaccines. **3. High-Yield Clinical Pearls for NEET-PG:** * **Storage:** Live vaccines are generally heat-labile (except OPV, which is the most heat-sensitive). * **Contraindications:** Live vaccines are strictly contraindicated in **pregnancy** and **immunocompromised individuals** (HIV with CD4 <200, malignancy, or steroid therapy). * **Exception:** Yellow Fever vaccine is a live vaccine but is mandatory for travel to certain regions despite general contraindications. * **Cold Chain:** Most live vaccines are stored at +2°C to +8°C, but the Diluent should never be frozen.

Question 1

What is the diluent used for BCG vaccine?

Accepted Answer

Normal saline

Answer

Distilled water

Answer

Dextrose solution

Answer

Ringer's lactate

Question 2

What is the total dose of Vitamin A given under the National Immunisation Schedule?

Accepted Answer

1.7 million IU

Answer

1.6 million IU

Answer

1.8 million IU

Answer

2.0 million IU

Question 3

What is the recommended dosing schedule for the oral typhoid vaccine?

Accepted Answer

Day 1, 3, 5

Answer

Day 1, 2, 3

Answer

Day 1, 2, 4

Answer

Day 1, 7, 14

Question 4

Which of the following can be given as post-exposure immunization?

Accepted Answer

Pertussis

Answer

Rabies

Answer

Measles

Answer

Yellow fever

Question 5

True about Oral Polio Vaccine (OPV) are all, EXCEPT?

Accepted Answer

Provides a quick immune response

Answer

It is a live vaccine

Answer

It is used in epidemics

Answer

Maternal antibodies interfere with its immune response

Question 6

Which of the following is NOT true about polio?

Accepted Answer

Vaccine-induced polio is usually due to Type 2 virus.

Answer

The Sabin vaccine is an attenuated, oral vaccine.

Answer

The Salk vaccine is a killed, formalized vaccine.

Answer

The most common type of poliovirus in epidemics is Type 1.

Question 7

Which of the following is NOT a vaccine-preventable disease?

Accepted Answer

Measles

Answer

Typhoid

Answer

Hepatitis B

Answer

Gonorrhea

Question 8

Typhoid revaccination is recommended every ... years in endemic areas?

Accepted Answer

3

Answer

1

Answer

5

Answer

10

Question 9

The shake test shown below can be done to know:

Accepted Answer

Whether the vaccine had been frozen at some point of time in the cold chain

Answer

Whether the vaccine was exposed to heat

Answer

Whether the expiry date of the vaccine has been reached

Answer

Whether the vaccine needs to be mixed with normal saline

Question 10

Which of the following statements regarding live vaccines is false?

Accepted Answer

Two live vaccines cannot be administered simultaneously

Answer

Booster doses are not required when live vaccines are administered

Answer

A single dose gives lifelong immunity

Answer

Live vaccines contain both major and minor antigens

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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