Vaccine and Vaccination — MCQs

Vaccine and Vaccination Indian Medical PG Practice Questions and MCQs

Question 31: Which of the following best describes the Hepatitis B vaccine?

A. Live attenuated vaccine
B. Killed vaccine (Correct Answer)
C. Toxoid
D. None of the above

Explanation: The Hepatitis B vaccine is a classic example of a **subunit vaccine**, which falls under the broader category of **killed/non-living vaccines**. ### **Explanation of the Correct Answer** The Hepatitis B vaccine currently used is a **recombinant DNA vaccine**. It is produced by inserting the gene for the Hepatitis B surface antigen (HBsAg) into yeast cells (*Saccharomyces cerevisiae*). These cells produce pure HBsAg particles, which are then harvested and purified. Since the vaccine contains only a specific protein component (the surface antigen) and no live viral DNA, it cannot replicate or cause disease. In the context of standard classification (Live vs. Killed), it is categorized as a **killed/inactivated vaccine** because it is non-infectious and non-replicating. ### **Why Other Options are Incorrect** * **A. Live attenuated vaccine:** These contain weakened forms of the whole virus (e.g., MMR, Varicella). Hepatitis B does not use a live virus, making it safe for immunocompromised individuals. * **C. Toxoid:** Toxoids are inactivated bacterial toxins (e.g., Tetanus, Diphtheria). Hepatitis B is a viral infection, not a toxin-mediated bacterial disease. ### **High-Yield Clinical Pearls for NEET-PG** * **First Recombinant Vaccine:** Hepatitis B was the first human vaccine produced using recombinant DNA technology. * **Schedule:** Standard 0, 1, and 6-month dosing. * **Site of Injection:** Always administered **Intramuscularly (IM) in the Deltoid muscle** (adults) or Anterolateral thigh (infants). **Gluteal injection is avoided** due to lower immunogenicity (fat interferes with antigen presentation). * **Protective Titer:** An Anti-HBs antibody titer of **>10 mIU/mL** is considered protective. * **Non-responders:** Individuals who fail to develop antibodies after two full series of vaccinations are termed "non-responders."

Question 32: Which of the following is/are subunit vaccines?

A. Typhoid Vi
B. Haemophilus influenzae type b vaccine (Hib)
C. Hepatitis B vaccine
D. All of the above (Correct Answer)

Explanation: ### Explanation **Concept:** Subunit vaccines do not contain the whole pathogen. Instead, they use only specific, purified components (antigens) like proteins, polysaccharides, or capsular fragments that are most capable of inducing a protective immune response. This reduces the risk of adverse reactions compared to whole-cell vaccines. **Analysis of Options:** * **Typhoid Vi:** This is a **capsular polysaccharide subunit vaccine** derived from the Vi (Virulence) antigen of *Salmonella Typhi*. Unlike the live-attenuated oral Ty21a vaccine, the Vi vaccine is injectable and contains only the purified surface polysaccharide. * **Haemophilus influenzae type b (Hib):** This is a **conjugate subunit vaccine**. It uses the purified capsular polysaccharide (Polyribosylribitol phosphate - PRP) conjugated to a carrier protein (like Tetanus toxoid) to enhance immunogenicity, especially in infants. * **Hepatitis B:** This is a **recombinant protein subunit vaccine**. It is produced by inserting the gene for the Hepatitis B surface antigen (HBsAg) into yeast cells (*Saccharomyces cerevisiae*), which then produce the protein used in the vaccine. Since all three options utilize specific components of the pathogen rather than the whole organism, **Option D (All of the above)** is correct. --- ### High-Yield Clinical Pearls for NEET-PG: * **Recombinant Subunit Vaccines:** Hepatitis B and HPV (Human Papillomavirus) are the classic examples. * **Polysaccharide vs. Conjugate:** Pure polysaccharide vaccines (like Pneumococcal PPSV23) are poorly immunogenic in children <2 years. Conjugation (as in Hib or PCV13) converts the T-cell independent response to a T-cell dependent one, inducing immunological memory. * **Acellular Pertussis (aP):** Another common subunit vaccine containing purified components like pertussis toxoid and filamentous hemagglutinin. * **Advantage:** They are safe for use in immunocompromised patients as they contain no live genetic material.

Question 33: Post-exposure vaccination is indicated for which of the following conditions?

A. Typhoid
B. Rabies (Correct Answer)
C. Mumps
D. None of the above

Explanation: **Explanation:** The correct answer is **Rabies**. Post-exposure prophylaxis (PEP) is effective when the incubation period of a disease is long enough to allow the vaccine-induced immune response to develop before the pathogen reaches its target organ. **1. Why Rabies is Correct:** Rabies has a variable and often long incubation period (typically 1–3 months). Because the virus travels via retrograde axonal transport to the CNS, there is a "window of opportunity" to administer the vaccine after exposure. The vaccine induces active immunity (neutralizing antibodies) that intercepts the virus before it reaches the central nervous system. In most clinical scenarios, Rabies PEP also includes Rabies Immunoglobulin (RIG) for immediate passive protection. **2. Why Incorrect Options are Wrong:** * **Typhoid:** This is a bacterial infection (Salmonella Typhi) with a relatively short incubation period (7–14 days). Vaccination is used for pre-exposure prophylaxis (travelers or endemic areas) but is ineffective after exposure. * **Mumps:** Mumps is a viral infection where the vaccine is part of the routine MMR schedule. While some live vaccines (like Measles) can be used post-exposure if given within 72 hours, Mumps vaccination does not provide documented protection once exposure has occurred. **3. NEET-PG High-Yield Pearls:** * **Other Post-Exposure Vaccines:** Apart from Rabies, post-exposure vaccination is indicated for **Hepatitis B, Varicella, and Measles**. * **Tetanus:** Often confused with PEP; however, if a wound is prone to tetanus, we administer a booster or TIG based on immunization history. * **Rabies Schedule (Post-exposure):** For non-immunized individuals, the intramuscular (Essen) schedule is **0, 3, 7, 14, and 28 days**. * **Site of Injection:** Rabies vaccine should be given in the **deltoid muscle** (adults) or anterolateral thigh (children). It should **never** be given in the gluteal region as fat reduces vaccine efficacy.

Question 34: What adjuvant is used in the DPT vaccine?

A. Aluminum (Correct Answer)
B. Magnesium
C. Zinc
D. Formaldehyde

Explanation: **Explanation:** **1. Why Aluminum is Correct:** Aluminum salts (specifically **Aluminum hydroxide** or **Aluminum phosphate**) are the most commonly used adjuvants in human vaccines, including the DPT (Diphtheria, Pertussis, and Tetanus) vaccine. An adjuvant is a substance added to a vaccine to enhance the body's immune response to an antigen. Aluminum works via the **"Depot Effect"**—it traps the vaccine antigens at the injection site, allowing for a slow, sustained release. This prolonged exposure recruits more antigen-presenting cells (APCs) and stimulates a stronger Th2 humoral immune response, leading to higher antibody titers. **2. Analysis of Incorrect Options:** * **B. Magnesium & C. Zinc:** These are essential minerals but are not used as adjuvants in standard vaccine formulations. They do not possess the necessary chemical properties to stabilize antigens or stimulate the immune system in this context. * **D. Formaldehyde:** This is a **preservative/inactivator**, not an adjuvant. Formaldehyde is used during the manufacturing process to detoxify bacterial toxins (turning them into toxoids) or to kill viruses, ensuring the vaccine is safe and non-pathogenic. **3. High-Yield Clinical Pearls for NEET-PG:** * **Toxoid Vaccines:** Diphtheria and Tetanus are toxoid vaccines; they always require an adjuvant because toxoids are poorly immunogenic on their own. * **Administration:** Vaccines containing aluminum adjuvants must be administered **intramuscularly (IM)**. If given subcutaneously, they can cause local irritation, granulomas, or "sterile abscesses." * **Freezing:** Aluminum-adjuvanted vaccines should **never be frozen**, as freezing destroys the adjuvant-antigen structure, reducing potency (the "Shake Test" is used to check for this). * **Other Adjuvants:** While Aluminum is the gold standard, newer adjuvants include **AS04** (used in HPV vaccines) and **MF59** (oil-in-water emulsion).

Question 35: Which of the following is a vaccine for cholera?

A. PPV23
B. Dukoral (Correct Answer)
C. Ty 21 a vaccine
D. JE-MB Nakayama

Explanation: ### Explanation **Correct Answer: B. Dukoral** **Dukoral** is an oral, killed whole-cell vaccine containing recombinant Cholera Toxin B-subunit (WC/rBS). It provides protection against *Vibrio cholerae* O1 (both Inaba and Ogawa serotypes) and offers short-term cross-protection against Enterotoxigenic *Escherichia coli* (ETEC) due to the similarity between cholera toxin and ETEC heat-labile toxin. **Analysis of Incorrect Options:** * **A. PPV23 (Pneumococcal Polysaccharide Vaccine):** This is a 23-valent vaccine used to prevent infections caused by *Streptococcus pneumoniae*. It is typically indicated for adults >65 years or individuals with chronic illnesses/asplenia. * **C. Ty21a:** This is a live-attenuated **oral typhoid vaccine** (Salmonella Typhi Ty21a strain). It is administered as enteric-coated capsules on alternate days (Days 1, 3, and 5). * **D. JE-MB Nakayama:** This refers to the **Japanese Encephalitis** Mouse Brain-derived inactivated vaccine. While historically significant, it has largely been replaced by newer vaccines like SA-14-14-2 (live) or Jenvac (inactivated). **High-Yield Clinical Pearls for NEET-PG:** * **Oral Cholera Vaccines (OCVs):** There are three WHO-prequalified OCVs: **Dukoral** (contains B-subunit), **Shanchol**, and **Euvichol** (both are bivalent O1 and O139, but without the B-subunit). * **Shanchol/Euvichol** are preferred for mass vaccination in endemic areas as they are cheaper and do not require a buffer. * **Route:** All modern cholera vaccines are administered **orally**. The older parenteral (injectable) killed vaccine is no longer recommended due to low efficacy and short duration of protection. * **Cross-protection:** Remember that Dukoral is the only one providing significant protection against **Traveler’s Diarrhea (ETEC)**.

Question 36: Which of the following diseases does NOT currently have an available vaccine?

A. Yellow fever
B. Japanese encephalitis
C. Dengue fever (Correct Answer)
D. Russian spring summer encephalitis

Explanation: **Explanation:** The correct answer is **Dengue fever**. While a vaccine (Dengvaxia) exists and is licensed in some countries, it is not part of the universal or routine immunization schedule in many regions, including India, due to safety concerns regarding "Antibody-Dependent Enhancement" (ADE). In seronegative individuals, the vaccine can act like a primary infection, leading to more severe disease (Dengue Shock Syndrome) upon subsequent natural infection. Therefore, for the purpose of standard medical examinations, it is often categorized as not having a "currently available/routinely used" vaccine compared to the other established options. **Analysis of Options:** * **Yellow Fever:** A highly effective live-attenuated vaccine (**17D strain**) is available. It provides lifelong immunity after a single dose and is mandatory for international travel to endemic zones (Africa/South America). * **Japanese Encephalitis (JE):** Multiple vaccines are available. In India, the live-attenuated **SA-14-14-2 strain** (derived from mice/cell culture) is used under the Universal Immunization Programme (UIP). * **Russian Spring-Summer Encephalitis (RSSE):** Inactivated cell-culture vaccines are available and used routinely in endemic regions of Eastern Europe and Russia. **High-Yield Clinical Pearls for NEET-PG:** 1. **Yellow Fever Vaccine:** Contraindicated in infants <6 months, pregnant women, and immunocompromised individuals. It is grown in **chick embryos**. 2. **JE Vaccine:** In the UIP, two doses are given (9 months and 16–24 months). 3. **Dengue:** The primary challenge in vaccine development is the need to provide equal protection against all four serotypes (DEN 1–4) simultaneously to avoid ADE.

Question 37: What is the recommended dose of Rubella immunoglobulin?

A. 5 ml
B. 10 ml
C. 20 ml (Correct Answer)
D. 40 ml

Explanation: **Explanation:** The correct answer is **20 ml (Option C)**. **Medical Concept:** Rubella (German Measles) is generally a mild disease; however, infection during early pregnancy can lead to **Congenital Rubella Syndrome (CRS)**, causing severe fetal defects. While the primary prevention strategy is live-attenuated vaccination (RA 27/3 strain), post-exposure prophylaxis with **Rubella Immunoglobulin (RIG)** is considered a "last resort" for non-immune pregnant women exposed to the virus who do not wish to undergo therapeutic abortion. The standard recommended dose of RIG is **20 ml** administered intramuscularly. It is important to note that RIG does not guarantee the prevention of fetal infection; it may only suppress clinical symptoms in the mother or prolong the incubation period. **Analysis of Options:** * **A (5 ml) & B (10 ml):** These doses are sub-therapeutic for Rubella prophylaxis. While smaller doses of specific immunoglobulins (like Hepatitis B or Tetanus) are used, Rubella requires a higher volume to achieve necessary antibody titers. * **D (40 ml):** This dose is excessively high and is not supported by standard clinical guidelines. **NEET-PG High-Yield Pearls:** * **Vaccine Strain:** RA 27/3 (Live attenuated, grown in human diploid cells). * **Contraindication:** Pregnancy is an absolute contraindication for the Rubella vaccine. Women should avoid pregnancy for **1 month** (previously 3 months) after vaccination. * **CRS Triad (Gregg’s Triad):** Cataract, Sensorineural deafness, and Cardiac defects (PDA/Pulmonary artery stenosis). * **Diagnosis:** IgM antibodies in the cord blood or infant serum are diagnostic of congenital infection.

Question 38: Meningococcal vaccine is available for all of the following serogroups, except?

A. Group A
B. Group B (Correct Answer)
C. Group C
D. Group Y

Explanation: **Explanation:** The correct answer is **Group B**. The primary reason for the absence of a traditional polysaccharide vaccine for *Neisseria meningitidis* Serogroup B lies in the concept of **molecular mimicry**. The capsular polysaccharide of Serogroup B consists of **α-2,8-linked sialic acid**, which is structurally identical to the sialic acid found on human neural cell adhesion molecules (NCAMs). Because the body recognizes this as "self," the polysaccharide is poorly immunogenic and carries a theoretical risk of inducing autoimmunity. Consequently, standard conjugate or polysaccharide vaccines (like those for A, C, Y, and W-135) cannot be developed for Group B. Instead, newer vaccines for Group B (e.g., Bexsero) utilize **recombinant proteins** rather than capsular polysaccharides. **Analysis of Options:** * **Option A (Group A):** This is a major cause of epidemics in the "Meningitis Belt" of Africa. It is included in both polysaccharide (MPSV4) and conjugate (MCV4) vaccines. * **Option C & D (Group C & Y):** These serogroups are common causes of endemic disease in developed countries. They are highly immunogenic and are standard components of the quadrivalent meningococcal vaccine (A, C, Y, W-135). **NEET-PG High-Yield Pearls:** 1. **Quadrivalent Vaccines:** Cover serogroups **A, C, Y, and W-135**. 2. **Vaccine Type:** Conjugate vaccines (MCV4) are preferred over pure polysaccharide vaccines (MPSV4) because they induce T-cell dependent immunity, providing longer protection and herd immunity. 3. **Group B Vaccine:** Developed using **Reverse Vaccinology**. It targets surface proteins (fHbp, NadA, NHBA) rather than the capsule. 4. **Most common serogroup in India:** Historically Group A, though Group W-135 and others are emerging.

Question 39: What is the role of Mg++ in vaccines?

A. Stabilizer (Correct Answer)
B. Preservative
C. Adjuvant
D. Vehicle

Explanation: **Explanation:** **1. Why Magnesium (Mg++) is the Correct Answer:** Magnesium ions ($Mg^{2+}$), typically in the form of Magnesium Chloride ($MgCl_2$), act as **thermal stabilizers**. Their primary role is to maintain the structural integrity and potency of the vaccine antigen (especially live-attenuated viruses) when exposed to heat. $Mg^{2+}$ prevents the thermal degradation of viral proteins and nucleic acids, ensuring the vaccine remains effective even if the cold chain is briefly compromised. * **Classic Example:** The Oral Polio Vaccine (OPV) uses $MgCl_2$ as a stabilizer to protect the live virus from heat-induced inactivation. **2. Why Other Options are Incorrect:** * **Preservative (e.g., Thiomersal, Phenol):** These are added to multi-dose vials to prevent the growth of bacteria or fungi. They do not stabilize the antigen itself. * **Adjuvant (e.g., Alum/Aluminum salts):** These are substances added to enhance or "boost" the body's immune response to the vaccine antigen. $Mg^{2+}$ does not have immunomodulatory properties. * **Vehicle (e.g., Normal Saline, Sterile Water):** This is the liquid medium (diluent) used to dissolve or suspend the vaccine components for administration. **3. High-Yield Clinical Pearls for NEET-PG:** * **OPV Stability:** $MgCl_2$ is the most high-yield stabilizer associated with OPV. * **Other Stabilizers:** Sugars (sucrose, lactose), amino acids (glycine), and proteins (gelatin, albumin) are also used as stabilizers. * **Adjuvant Fact:** Aluminum hydroxide/phosphate (Alum) is the most common adjuvant; it is **never** used in live vaccines (like BCG or OPV) as it can interfere with viral replication. * **Thiomersal:** A mercury-containing preservative used in DPT and Hepatitis B vaccines, but absent in single-dose live vaccines.

Question 40: Which vaccine is contraindicated in patients with AIDS?

A. DPT
B. BCG (Correct Answer)
C. Rabies
D. Measles

Explanation: **Explanation:** The core concept here is the safety profile of **Live Attenuated Vaccines** in immunocompromised individuals. **Why BCG is the correct answer:** BCG (Bacillus Calmette-Guérin) is a live attenuated vaccine derived from *Mycobacterium bovis*. In patients with AIDS (CD4 count <200 cells/mm³), the immune system cannot contain even the weakened vaccine strain. This can lead to **"Disseminated BCG-osis,"** a life-threatening systemic infection. Therefore, BCG is strictly contraindicated in symptomatic HIV/AIDS patients. **Analysis of Incorrect Options:** * **DPT (Option A):** This is a combination of toxoids (Diphtheria, Tetanus) and a killed/subunit component (Pertussis). Inactivated vaccines are safe in AIDS patients, though their immunogenicity (effectiveness) may be reduced. * **Rabies (Option B):** The modern Rabies vaccine (PCECV/HDCV) is a **killed (inactivated) vaccine**. It is safe to administer and is mandatory for post-exposure prophylaxis regardless of immune status. * **Measles (Option D):** While Measles is a live vaccine, it is a unique exception. WHO and NACP guidelines state that Measles vaccine **should** be given to HIV-infected children unless they are *severely* immunocompromised, because the risk of lethal natural measles outweighs the vaccine risk. However, BCG remains the "most" contraindicated among the choices provided. **NEET-PG High-Yield Pearls:** * **General Rule:** All live vaccines (BCG, OPV, Yellow Fever, Varicella) are generally contraindicated in immunocompromised states. * **The HIV Exception:** Measles and MMR can be given if the patient is not severely immunocompromised. * **Asymptomatic HIV:** In infants born to HIV+ mothers who are asymptomatic, BCG can be given in high-prevalence areas, but once symptoms of AIDS develop, it is contraindicated. * **Avoid OPV:** In a household with an AIDS patient, OPV should be replaced with IPV to prevent vaccine-derived poliovirus shedding.

Practice by Chapter

Principles of Immunization

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Types of Vaccines

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Vaccine Development and Production

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Routine Immunization Schedule

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Adverse Events Following Immunization

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Cold Chain and Vaccine Delivery

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New Vaccine Technologies

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Vaccination in Special Populations

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Herd Immunity and Population Protection

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Anti-vaccination Movement and Hesitancy

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National Immunization Programs

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Future of Vaccines

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