Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 221: After vaccination against Japanese encephalitis, when does immunity typically develop?

A. 30 days (Correct Answer)
B. 7 days
C. 10 days
D. 21 days

Explanation: **Explanation:** The development of protective immunity following Japanese Encephalitis (JE) vaccination is a gradual process. In the context of the **live attenuated SA 14-14-2 vaccine** (the strain most commonly used in the Universal Immunization Programme in India), protective antibodies typically reach significant levels approximately **one month (30 days)** after the administration of a single dose. **Why 30 days is correct:** Immunological studies indicate that while seroconversion begins earlier, the peak primary immune response and the establishment of robust, protective neutralizing antibody titers (PRNT titers ≥1:10) generally stabilize around the 30-day mark. This duration allows for the necessary viral replication of the attenuated strain and subsequent B-cell activation and maturation. **Analysis of incorrect options:** * **7 and 10 days:** These timeframes are too short for a primary immune response to generate sufficient IgG titers for neurotropic viruses like JE. At this stage, the body is primarily in the innate and early IgM phase. * **21 days:** While some individuals may show immunity by three weeks, 30 days is the standard clinical benchmark used in public health guidelines and textbooks (like Park’s PSM) to ensure reliable protection. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine Strain:** The SA 14-14-2 is a live attenuated vaccine derived from primary hamster kidney cells. * **Schedule (UIP):** Two doses are given under the Universal Immunization Programme—the 1st dose at **9 months** (with Measles/MR) and the 2nd dose at **16–24 months** (with DPT booster). * **Route:** Subcutaneous (0.5 ml). * **Vector:** Transmitted by the **Culex tritaeniorhynchus** mosquito, which breeds in stagnant water (paddy fields). * **Reservoir:** Pigs (amplifier host) and Ardeid birds (natural reservoir). Humans are **dead-end hosts**.

Question 222: Which of the following vaccinations is absolutely contraindicated in pregnancy?

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

Explanation: **Explanation:** The core principle in obstetric immunization is that **Live Attenuated Vaccines** are generally contraindicated during pregnancy due to the theoretical risk of the vaccine virus crossing the placenta and causing fetal infection. **Yellow Fever (Option D)** is a live attenuated viral vaccine. It is absolutely contraindicated in pregnancy because of the potential risk of vertical transmission and fetal harm. It should only be considered in high-risk scenarios where travel to an endemic area is unavoidable and the risk of the disease outweighs the risk of vaccination. **Analysis of Incorrect Options:** * **Hepatitis B (Option A):** This is a **subunit (recombinant)** vaccine. It contains no live virus and is safe and recommended for pregnant women at high risk of infection. * **Cholera (Option B):** Modern cholera vaccines are **killed/inactivated** (oral or injectable). Inactivated vaccines are generally considered safe during pregnancy if the risk of exposure is high. * **Rabies (Option C):** This is an **inactivated** vaccine. Because rabies is 100% fatal, pregnancy is never a contraindication for post-exposure prophylaxis. It is safe for both mother and fetus. **High-Yield NEET-PG Pearls:** 1. **Live Vaccines Contraindicated:** Remember the mnemonic **"Rome Is My Very Best Vacation"** (Rubella, Oral Polio, Measles, Mumps, Varicella, BCG, Yellow Fever). 2. **Exception:** If a pregnant woman is traveling to a high-risk Yellow Fever zone, the vaccine may be given under strict medical supervision, but it remains the "most contraindicated" among the options provided. 3. **Safe Vaccines:** Tetanus, Diphtheria, and Pertussis (Tdap) are not only safe but routinely recommended during pregnancy (usually between 27–36 weeks) to provide passive immunity to the newborn.

Question 223: Who was the pioneer in the concept of specific protection by vaccine?

A. Chinese (Correct Answer)
B. Robert Koch
C. Ambroise Paré
D. Louis Pasteur

Explanation: **Explanation:** The concept of **Specific Protection** refers to measures taken to prevent the occurrence of a specific disease. The historical pioneer of this concept is the **Chinese**, who practiced **Variolation** as early as the 10th century. This involved the deliberate inoculation of material from smallpox pustules (via inhalation or skin scratching) into healthy individuals to induce a mild form of the disease, thereby granting lifelong immunity. This predates Edward Jenner’s cowpox vaccine (1796) by centuries. **Analysis of Options:** * **Chinese (Correct):** Credited with the earliest form of immunization (variolation) against smallpox, establishing the foundation for specific protection. * **Robert Koch:** Known as the "Father of Bacteriology." He discovered the causative agents of Anthrax, Cholera, and Tuberculosis (Koch’s Postulates) but was not the pioneer of vaccination. * **Ambroise Paré:** A French surgeon considered the "Father of Modern Surgery." He revolutionized the treatment of wounds but had no role in the development of vaccines. * **Louis Pasteur:** Known as the "Father of Microbiology." While he developed vaccines for Anthrax and Rabies and coined the term "Vaccine" (in honor of Jenner), he was not the first to practice the concept of specific protection. **NEET-PG High-Yield Pearls:** * **Levels of Prevention:** Specific protection is a component of **Primary Prevention**. * **Edward Jenner:** Performed the first scientific vaccination (using cowpox for smallpox) in 1796. * **Louis Pasteur:** Developed the first **live attenuated vaccines**. * **Smallpox:** The only human disease to be globally eradicated (declared by WHO on May 8, 1980).

Question 224: All of the following are true of the BCG vaccine except:

A. Dose is 0.1 ml
B. Administered subcutaneously (Correct Answer)
C. Uses the Danish 1331 strain
D. It is a live attenuated vaccine

Explanation: **Explanation:** The BCG (Bacillus Calmette-Guérin) vaccine is a **live attenuated vaccine** derived from *Mycobacterium bovis*. The correct answer is **B** because BCG is strictly administered via the **intradermal route**, not subcutaneously. 1. **Why Option B is correct (The Exception):** BCG must be given intradermally (usually over the left deltoid) using an insulin or tuberculin syringe (26G). If injected subcutaneously, it can lead to severe local complications such as abscess formation or regional lymphadenitis. 2. **Why other options are incorrect:** * **Option A:** The standard dose for infants over 4 weeks of age is **0.1 ml**. (Note: For neonates below 4 weeks, the dose is 0.05 ml to prevent excessive scarring). * **Option C:** The **Danish 1331 strain** is the most commonly used strain globally and in India for vaccine production. * **Option D:** BCG is a classic example of a **live attenuated bacterial vaccine**. **High-Yield Clinical Pearls for NEET-PG:** * **Diluent:** Normal Saline (NS) is used. Distilled water is avoided as it causes irritation. * **Storage:** It is heat-sensitive and light-sensitive; supplied in dark-colored ampoules and must be used within 4–6 hours of reconstitution. * **Phenomenon:** A papule forms at 2–3 weeks, followed by a crust/ulcer at 5–6 weeks, eventually leaving a permanent **pitted scar** by 6–12 weeks. * **Protective Effect:** It provides high protection against disseminated forms (Miliary TB and TB Meningitis) but has variable efficacy (0–80%) against adult pulmonary TB.

Question 225: What is the ideal recommended time for observation following immunization for adverse events following immunization (AEFI)?

A. 15 minutes
B. 30 minutes (Correct Answer)
C. 45 minutes
D. 1 hour

Explanation: **Explanation:** The correct answer is **30 minutes (Option B)**. **1. Why it is correct:** The primary purpose of post-vaccination observation is the early detection and management of immediate **anaphylactic reactions**. Anaphylaxis is a life-threatening, Type-I hypersensitivity reaction that typically occurs within minutes of exposure to an allergen. According to the **Universal Immunization Programme (UIP)** and **WHO guidelines**, every vaccine recipient must be observed for at least 30 minutes at the session site. This "waiting period" ensures that if a severe allergic reaction occurs, trained healthcare personnel can intervene immediately with Adrenaline (1:1000). **2. Why other options are incorrect:** * **15 minutes (Option A):** While some mild reactions occur early, 15 minutes is insufficient to capture the majority of immediate-onset anaphylactic events. * **45 minutes & 1 hour (Options C & D):** While longer observation is safer, it is logistically impractical for mass immunization campaigns and routine clinics. 30 minutes is the established gold standard that balances safety with public health efficiency. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice for Anaphylaxis:** Adrenaline (Epinephrine) 1:1000 concentration, administered **Intramuscularly (IM)** in the anterolateral aspect of the thigh. * **AEFI Surveillance:** AEFI is defined as any untoward medical occurrence following immunization, which does not necessarily have a causal relationship with the vaccine. * **Cold Chain:** Most UIP vaccines are stored between **+2°C to +8°C**. * **Most Heat Sensitive Vaccine:** Oral Polio Vaccine (OPV). * **Most Freeze Sensitive Vaccine:** Hepatitis B and DPT/Pentavalent.

Question 226: Which of the following vaccines is not given to an unimmunized 8-year-old male child?

A. Inactivated polio vaccine
B. Hepatitis B vaccine
C. Acellular pertussis vaccine (Correct Answer)
D. Measles vaccine

Explanation: **Explanation:** The correct answer is **Acellular pertussis vaccine (Option C)**. **Why it is correct:** The primary medical concept here is the age-related risk of adverse reactions to the whole-cell or acellular pertussis component. In the National Immunization Schedule (NIS) and IAP guidelines, pertussis-containing vaccines (DTwP or DTaP) are generally **not recommended for children above 7 years of age**. This is because the risk of local and systemic reactions (such as high fever and severe local swelling) increases significantly with age, while the severity of pertussis disease decreases in older children. For children >7 years requiring protection, the **Tdap** vaccine (reduced dose of diphtheria and acellular pertussis) is used instead of the standard DTaP/acellular pertussis vaccine. **Why other options are incorrect:** * **Inactivated Polio Vaccine (IPV):** Can be given at any age to an unimmunized individual to provide protection against poliomyelitis. * **Hepatitis B Vaccine:** This is a "catch-up" vaccine that can be administered at any age if the child was not previously immunized. * **Measles Vaccine:** Measles remains a significant threat to non-immune individuals of any age. An unimmunized 8-year-old should receive two doses of a measles-containing vaccine (usually MMR). **High-Yield Clinical Pearls for NEET-PG:** * **Cut-off Age:** 7 years is the threshold. Below 7 years, use **DTwP/DTaP** (capital 'D' and 'P' for full strength). Above 7 years, use **Tdap** (small 'd' and 'p' for reduced antigen content). * **Tetanus Toxoid (TT) Replacement:** In the current Universal Immunization Programme (UIP), TT has been replaced by **Td (Tetanus and adult-dose Diphtheria)** for school-age children (10 and 16 years) to maintain diphtheria immunity. * **Contraindication:** A history of encephalopathy within 7 days of a previous pertussis dose is an absolute contraindication for any further pertussis-containing vaccines.

Question 227: Reverse Cold Chain is used for what purpose?

A. Transportation of vaccines at +2 to +8 degrees Celsius from PHC to sub-centre
B. Transportation of Oral Polio vaccine at -20 to -40 degrees Celsius
C. Transportation of poliomyelitis stool samples from the field to the laboratory (Correct Answer)
D. None of the above

Explanation: ### Explanation **Correct Answer: C. Transportation of poliomyelitis stool samples from the field to the laboratory** The **Reverse Cold Chain** is a specialized logistics system used to maintain the viability of pathogens in clinical specimens during transport from the field to a diagnostic laboratory. In the context of the **Global Polio Eradication Initiative**, it is specifically used for **Acute Flaccid Paralysis (AFP) surveillance**. Since the Poliovirus is thermolabile, stool samples must be kept at **2°C to 8°C** to prevent the virus from denaturing, ensuring it can be successfully isolated in a laboratory culture. #### Analysis of Incorrect Options: * **Option A:** This describes the standard **Cold Chain** (forward chain), which ensures vaccines remain potent from the manufacturer to the beneficiary. * **Option B:** While OPV is stored at sub-zero temperatures at regional/district levels, this is part of the standard storage protocol, not the "reverse" process. #### NEET-PG High-Yield Pearls: * **AFP Surveillance Requirement:** Two stool samples must be collected **24–48 hours apart** within **14 days** of the onset of paralysis. * **Condition of Sample:** A sample is considered "adequate" if it reaches the lab within 72 hours of collection, under ice, with the "Reverse Cold Chain" intact. * **Ice Packs:** In a Reverse Cold Chain, stool samples are placed in a plastic bag, which is then placed inside a vaccine carrier with **conditioned ice packs**. * **VVM (Vaccine Vial Monitor):** Remember that VVM is for the *forward* cold chain to check vaccine potency; it is not used in the reverse cold chain.

Question 228: Thrombocytopenia is an adverse reaction of which vaccine?

A. BCG
B. DPT
C. MMR (Correct Answer)
D. Hep B

Explanation: **Explanation:** The correct answer is **MMR (Measles, Mumps, and Rubella)**. **Why MMR is the correct answer:** Immune Thrombocytopenic Purpura (ITP) is a recognized, though rare, adverse event following immunization (AEFI) specifically associated with the **Measles** component of the MMR vaccine. The underlying mechanism is believed to be **molecular mimicry**, where vaccine-induced antibodies cross-react with surface antigens on the patient’s platelets, leading to their destruction in the spleen. This typically occurs within 6 weeks of vaccination and is usually self-limiting. **Why other options are incorrect:** * **BCG:** Common adverse effects include local lymphadenitis and cold abscesses. It is not associated with platelet disorders. * **DPT:** Known for local reactions (pain, swelling) and systemic reactions like fever or persistent crying. The Pertussis component is rarely linked to encephalopathy, but not thrombocytopenia. * **Hep B:** The most significant (though rare) serious adverse effect is anaphylaxis. It is also occasionally linked to hypersensitivity reactions, but thrombocytopenia is not a characteristic feature. **High-Yield Clinical Pearls for NEET-PG:** * **Risk Ratio:** The risk of thrombocytopenia after MMR vaccination is approximately 1 in 30,000 doses—significantly lower than the risk of thrombocytopenia following a natural Measles or Rubella infection. * **Other MMR Side Effects:** Febrile seizures (due to the Measles component) and transient arthralgia (due to the Rubella component). * **Contraindication:** MMR is a **Live Attenuated Vaccine** and is contraindicated in pregnancy and severely immunocompromised individuals. * **Storage:** MMR is highly heat-sensitive and must be stored at +2°C to +8°C, protected from light.

Question 229: A resident sustains a needle-stick injury from a patient positive for HBsAg and HBeAg who is not immunized. What is the appropriate management?

A. No intervention needed
B. Combined active and passive immunization (Correct Answer)
C. Active immunization only
D. Passive immunization only

Explanation: ### Explanation **Correct Answer: B. Combined active and passive immunization** The management of a needle-stick injury (NSI) depends on the vaccination status of the healthcare worker (HCW) and the HBsAg status of the source. In this scenario, the source is highly infectious (HBeAg positive), and the resident is unimmunized. **Why it is correct:** For an **unvaccinated individual** exposed to an HBsAg-positive source, the goal is to provide immediate protection while ensuring long-term immunity. 1. **Passive Immunization:** Hepatitis B Immunoglobulin (HBIG) provides immediate, pre-formed antibodies to neutralize the virus during the incubation period. It should ideally be given within 24 hours (up to 7 days). 2. **Active Immunization:** The Hepatitis B vaccine series is started simultaneously (at a different injection site) to stimulate the body’s own immune system for long-term protection. **Why incorrect options are wrong:** * **Option A:** Incorrect because Hepatitis B is highly transmissible via NSI (risk is ~30% if the source is HBeAg positive). Doing nothing poses a high risk of chronic infection. * **Option C:** Active immunization alone is insufficient because the vaccine takes weeks to produce protective antibody titers (anti-HBs ≥10 mIU/mL), leaving a "window period" of vulnerability. * **Option D:** Passive immunization alone provides only temporary protection (half-life of ~3 weeks) and does not prevent future infections. --- ### High-Yield NEET-PG Pearls * **The "Rule of 3" for NSI Risk:** HBV (30%), HCV (3%), HIV (0.3%). * **HBIG Dose:** 0.06 mL/kg IM. * **Site:** HBIG and the HBV vaccine must be administered at **different anatomical sites** (e.g., left vs. right deltoid) to prevent the immunoglobulin from neutralizing the vaccine antigen. * **Post-Exposure Prophylaxis (PEP) for Vaccinated HCWs:** If the HCW is a "known responder" (anti-HBs ≥10 mIU/mL), no treatment is needed regardless of the source status. If the HCW is a "non-responder" (after 2 vaccine series), two doses of HBIG are preferred.

Question 230: Toxic shock syndrome is mostly associated with which vaccine?

A. Mumps
B. Measles (Correct Answer)
C. Salk
D. Tetanus

Explanation: **Explanation:** **Toxic Shock Syndrome (TSS)** in the context of immunization is a severe, life-threatening complication primarily associated with the **Measles vaccine**. **Why Measles is the correct answer:** The association is not due to the vaccine virus itself, but due to **bacterial contamination** (specifically *Staphylococcus aureus*) of the multi-dose vial. The measles vaccine is a live-attenuated lyophilized (freeze-dried) vaccine that requires reconstitution with a diluent. Once reconstituted, it lacks preservatives and serves as an excellent culture medium for bacteria if kept at room temperature for prolonged periods. If a contaminated vial is used beyond the recommended 4 hours, *S. aureus* can multiply and produce toxins, leading to rapid-onset high fever, vomiting, diarrhea, and circulatory collapse (Toxic Shock Syndrome) in vaccine recipients. **Why other options are incorrect:** * **Mumps:** While also a live vaccine, historical clusters of TSS have been overwhelmingly linked to Measles immunization programs in field settings. * **Salk (IPV):** This is an inactivated (killed) vaccine usually supplied in pre-filled syringes or vials with preservatives, significantly lowering the risk of contamination-induced TSS. * **Tetanus:** Tetanus toxoid is a highly stable, adsorbed vaccine. While sterile abscesses can occur, it is not classically associated with the TSS outbreaks seen with reconstituted live vaccines. **High-Yield Clinical Pearls for NEET-PG:** * **The "4-Hour Rule":** Reconstituted Measles, BCG, and JE vaccines must be discarded after 4 hours or at the end of the session, whichever comes first. * **Most common organism:** *Staphylococcus aureus* is the most common cause of vaccine-associated TSS. * **Clinical Presentation:** Symptoms usually appear within 6–12 hours of vaccination (much faster than the incubation period of the vaccine virus itself). * **Prevention:** Strict adherence to the cold chain and aseptic reconstitution techniques.

Practice by Chapter

Principles of Immunization

Practice Questions

Types of Vaccines

Practice Questions

Universal Immunization Program

Practice Questions

Cold Chain System

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Vaccine Storage and Handling

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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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