Vaccine and Vaccination — MCQs

Vaccine and Vaccination Indian Medical PG Practice Questions and MCQs

Question 21: The OKA strain is used to produce a vaccine for which disease?

A. Mumps
B. Measles
C. Japanese encephalitis
D. Chickenpox (Correct Answer)

Explanation: **Explanation:** The **Oka strain** is the specific live-attenuated strain of the **Varicella-Zoster Virus (VZV)** used to produce vaccines against **Chickenpox** (Varicella) and Shingles (Herpes Zoster). It was originally isolated in Japan from the vesicle fluid of a healthy child (named Oka) and subsequently attenuated through serial passage in human and guinea pig cell lines. **Analysis of Options:** * **Chickenpox (Correct):** The Oka strain is the gold standard for both the monovalent Varicella vaccine and the combination MMRV vaccine. It is also used in a higher titer in the Zoster vaccine (Zostavax) to prevent shingles in the elderly. * **Mumps (Incorrect):** The most common strain used for Mumps vaccination is the **Jeryl Lynn strain**. Other strains include Urabe and Leningrad-Zagreb. * **Measles (Incorrect):** The standard strain used globally for Measles vaccination is the **Edmonston-Zagreb** or **Schwartz strain**. * **Japanese Encephalitis (Incorrect):** The live-attenuated vaccine for JE uses the **SA 14-14-2 strain**. Inactivated vaccines (like JENVAC) use the Kolar strain. **High-Yield Clinical Pearls for NEET-PG:** * **Route:** Varicella vaccine is administered **Subcutaneously (SC)**. * **Schedule:** Usually given at 12–15 months, with a booster at 4–6 years. * **Post-exposure Prophylaxis:** The vaccine is effective if given within **3–5 days** of exposure. * **Contraindications:** Being a live vaccine, it is contraindicated in pregnancy and severely immunocompromised individuals. * **Breakthrough Varicella:** Refers to a mild clinical infection occurring in a vaccinated individual, usually characterized by <50 lesions and no fever.

Question 22: Pneumococcal polysaccharide vaccine (PPV23) is not recommended in which of the following patient groups?

A. Patients with sickle cell disease
B. Immunocompromised patients (Correct Answer)
C. Post-splenectomy patients
D. Patients with Diabetes mellitus

Explanation: **Explanation:** The **Pneumococcal Polysaccharide Vaccine (PPV23)** contains purified capsular polysaccharides from 23 serotypes. The core immunological concept here is that polysaccharides are **T-cell independent antigens**. They stimulate B-cells directly without the help of T-helper cells, leading to a poor immune response in individuals with weakened immune systems. * **Why Option B is Correct:** In **immunocompromised patients** (e.g., those with HIV, malignancy, or on immunosuppressants), the B-cell response is often suboptimal. Furthermore, PPV23 does not induce mucosal immunity or immunological memory. Therefore, the **Pneumococcal Conjugate Vaccine (PCV13/15/20)** is preferred first in these patients because the protein conjugate triggers a T-cell dependent response, ensuring better immunogenicity and memory. * **Why Options A, C, and D are Incorrect:** * **Sickle Cell Disease (A) and Post-splenectomy (C):** These patients are at high risk for infections by encapsulated bacteria (like *S. pneumoniae*). While they receive PCV series, PPV23 is specifically indicated as a booster to expand serotype coverage. * **Diabetes Mellitus (D):** This is a chronic medical condition where PPV23 is recommended to reduce the risk of invasive pneumococcal disease. **High-Yield Clinical Pearls for NEET-PG:** * **Age Factor:** PPV23 is generally not given to children **<2 years old** because their immune systems cannot respond to T-cell independent antigens. * **Conjugate vs. Polysaccharide:** PCV (e.g., Prevnar) induces **IgG** and mucosal **IgA** (reducing carriage), whereas PPV23 primarily induces **IgM**. * **Sequence:** In high-risk adults, the Conjugate vaccine is typically given first, followed by PPV23 after 8 weeks to provide the "broadest" protection.

Question 23: Anti-rabies vaccine is prepared from:

A. Wild virus
B. Live attenuated virus
C. Street virus
D. Fixed virus (Correct Answer)

Explanation: **Explanation:** The correct answer is **Fixed virus**. This distinction is fundamental to the history and production of rabies vaccines. **1. Why "Fixed Virus" is Correct:** A **Fixed virus** is a strain of rabies virus that has been stabilized (its incubation period is "fixed") through repeated serial passages in a specific host, such as rabbits or cell cultures. This process makes the virus highly predictable and neurotropic but significantly reduces its ability to cause disease in humans. Because of its stable incubation period (usually 4–6 days) and consistent behavior, it is the preferred substrate for manufacturing both inactivated (killed) and live-attenuated vaccines. **2. Why the other options are incorrect:** * **Street Virus (Option C):** This refers to the virus as it exists in nature (isolated from a rabid animal). It has a highly variable incubation period (weeks to months) and is extremely pathogenic. It is never used for vaccines because its behavior is unpredictable. * **Wild Virus (Option A):** This is essentially a synonym for the Street virus. It represents the naturally occurring, virulent strain. * **Live Attenuated Virus (Option B):** While some veterinary rabies vaccines use attenuated strains, the standard human anti-rabies vaccines (ARV) used today (like PCECV or HDCV) are **inactivated (killed)** vaccines derived from fixed virus strains. **High-Yield Clinical Pearls for NEET-PG:** * **Louis Pasteur:** He developed the first rabies vaccine by serial passage in rabbit spinal cords, effectively "fixing" the virus. * **Incubation Period:** The "Fixed" virus has a short, constant incubation period (4–6 days), whereas the "Street" virus has a long, variable one (1–3 months). * **Negri Bodies:** These are characteristic intracytoplasmic inclusion bodies found in neurons infected with **Street virus**, but they are usually **absent** in infections caused by Fixed virus. * **Current Vaccines:** Modern vaccines (Cell Culture Vaccines) use the **Pitman-Moore strain**, which is a type of fixed virus.

Question 24: Which of the following is a live oral vaccine?

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

Explanation: **Explanation:** The correct answer is **Typhoid (specifically the Ty21a strain)**. In the context of NEET-PG, it is crucial to distinguish between the different formulations of vaccines and their routes of administration. 1. **Typhoid (Ty21a):** This is a **live attenuated** vaccine administered **orally** (usually as enteric-coated capsules). It provides mucosal immunity by stimulating GALT (Gut-Associated Lymphoid Tissue). Note that the other common typhoid vaccine, Vi polysaccharide, is injectable and subunit-based. 2. **BCG (Bacillus Calmette–Guérin):** While this is a live attenuated vaccine (derived from *Mycobacterium bovis*), it is administered **intradermally**, not orally. 3. **Measles:** This is a live attenuated vaccine (Edmonston-Zagreb strain in India) administered via the **subcutaneous** route. 4. **Rabies:** All modern rabies vaccines (like PCECV or HDCV) are **killed/inactivated** vaccines and are administered **intramuscularly** or intradermally (IDRV). There is no human oral rabies vaccine. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Live Vaccines:** "**B**oy **R**omeo **G**ive **M**y **L**ove **S**picy **T**ypical **Y**ellow **F**ever" (**B**CG, **R**ubella/Rotavirus, **G**erman Measles, **M**umps/Measles, **L**ive Polio/OPV, **S**mallpox, **T**yphoid (oral), **Y**ellow **F**ever). * **Oral Live Vaccines:** The two most commonly tested are **OPV (Sabin)** and **Oral Typhoid (Ty21a)**. Rotavirus is also a live oral vaccine. * **Ty21a Schedule:** Administered on days 1, 3, and 5 (3 doses). It should not be taken concurrently with antibiotics. * **Contraindication:** Live vaccines are generally contraindicated in pregnancy and immunocompromised states (except HIV patients before the symptomatic stage).

Question 25: Nervous tissue Rabies vaccines are usually manufactured from which source?

A. Duck embryos
B. Human diploid cells
C. Sheep brain tissue (Correct Answer)
D. Chick embryos

Explanation: **Explanation:** The correct answer is **Sheep brain tissue**. Historically, the first generation of rabies vaccines was derived from nervous tissue. The most prominent example is the **Semple vaccine**, which is produced by inoculating the rabies virus into the brains of sheep. The virus is then inactivated using phenol. While effective at inducing immunity, these vaccines are now largely obsolete in modern medicine due to the high risk of **neuroparalytic complications** (such as Acute Disseminated Encephalomyelitis - ADEM) caused by the presence of myelin basic protein in the sheep brain substrate. **Analysis of Incorrect Options:** * **Duck embryos (Option A):** These were used to create the Duck Embryo Vaccine (DEV) to reduce the risk of neurological side effects associated with nervous tissue vaccines, but they were less immunogenic. * **Human diploid cells (Option B):** These are used to produce the **Human Diploid Cell Vaccine (HDCV)**. This is a modern, "cell culture" vaccine and is considered the **gold standard** for rabies prophylaxis due to its high efficacy and safety profile. * **Chick embryos (Option D):** These are used for the **Purified Chick Embryo Cell (PCEC)** vaccine, another modern cell culture vaccine commonly used today. **High-Yield Clinical Pearls for NEET-PG:** * **Neural vs. Non-neural:** Neural vaccines (Semple/Sheep brain) require 14 daily injections; modern Cell Culture Vaccines (CCVs) require only 4–5 doses. * **WHO Recommendation:** The WHO has recommended the total replacement of nervous tissue vaccines with modern cell culture vaccines. * **Incubation Period:** Rabies has a highly variable incubation period (usually 1–3 months), making post-exposure prophylaxis (PEP) extremely effective if started early. * **Site of Injection:** Modern rabies vaccines must be given **intramuscularly in the deltoid** (adults) or anterolateral thigh (children). **Never** in the gluteal region, as fat interferes with absorption.

Question 26: Which of the following is a killed vaccine?

A. Hepatitis A (Correct Answer)
B. Measles
C. Oral Polio Vaccine (OPV)
D. Bacillus Calmette-Guérin (BCG)

Explanation: **Explanation:** The correct answer is **Hepatitis A**. Vaccines are broadly classified into live-attenuated, killed (inactivated), subunit, and toxoid types. Understanding this classification is high-yield for NEET-PG. **1. Why Hepatitis A is correct:** The Hepatitis A vaccine is a classic example of a **killed (inactivated) vaccine**. It is prepared by growing the virus in cell culture and subsequently inactivating it using chemicals like formaldehyde. Since the virus is dead, it cannot replicate or cause disease, making it safe for immunocompromised individuals, though it typically requires booster doses for long-term immunity. **2. Why the other options are incorrect:** * **Measles:** This is a **live-attenuated** viral vaccine. It is part of the MMR/MR vaccine and is contraindicated in pregnancy and severe immunosuppression. * **Oral Polio Vaccine (OPV/Sabin):** This is a **live-attenuated** vaccine. In contrast, the Injectable Polio Vaccine (IPV/Salk) is the killed version. * **BCG (Bacillus Calmette-Guérin):** This is a **live-attenuated bacterial** vaccine derived from *Mycobacterium bovis*. It is the most widely used vaccine globally for tuberculosis prevention. **Clinical Pearls for NEET-PG:** * **Mnemonic for Killed Vaccines:** "**K**illed **P**olio (**S**alk), **R**abies, **I**nfluenza (injected), **H**epatitis **A**, and **P**ertussis" (**K**illed **PR**I**H**A**P**). * **Mnemonic for Live Vaccines:** "**B**oy **L**oves **T**he **C**rimean **M**y **R**uby **S**lipper **V**ery **P**olitely" (**B**CG, **L**ike Typhoid/Oral, **T**ularemia, **C**holera/Oral, **M**easles, **M**umps, **R**ubella, **S**mallpox, **V**aricella, **P**olio/Oral). * **Key Distinction:** Hepatitis B is a **Recombinant/Subunit** vaccine (HBsAg), whereas Hepatitis A is **Killed**.

Question 27: BCG is a?

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

Explanation: **Explanation:** **BCG (Bacillus Calmette-Guérin)** is the correct answer because it is a **live attenuated vaccine** derived from an attenuated (weakened) strain of *Mycobacterium bovis*. It was developed by Calmette and Guérin through 230 serial subcultures over 13 years to reduce virulence while maintaining immunogenicity. **Analysis of Options:** * **Live attenuated vaccine (Correct):** BCG contains live bacteria that multiply within the host to stimulate a potent cell-mediated immune response (Type IV hypersensitivity), which is essential for protection against intracellular pathogens like *M. tuberculosis*. * **Immunomodulator:** While BCG is used as an immunomodulator (e.g., intravesical therapy for bladder cancer), its primary classification in the context of immunization is a vaccine. * **Killed vaccine:** These contain inactivated pathogens (e.g., Salk Polio, Rabies). BCG must be live to be effective; if the bacilli are killed, the vaccine fails to induce protective immunity. * **Toxoid vaccine:** These are made from inactivated bacterial toxins (e.g., Tetanus, Diphtheria). BCG is a whole-cell bacterial vaccine, not a toxin-based one. **High-Yield Clinical Pearls for NEET-PG:** * **Strain used:** Danish 1331 strain is the most commonly used globally. * **Dose:** 0.1 mL (0.05 mL for neonates under 4 weeks). * **Route:** Strictly **intradermal** (using a tuberculin/Omega syringe) over the left deltoid. * **Reconstitution:** Must be reconstituted with **Normal Saline**. Never use Distilled Water (causes irritation). * **Stability:** Once reconstituted, it must be used within **3–6 hours** or discarded due to the risk of contamination and loss of potency. * **Phenomenon:** It produces a characteristic permanent scar. If given to a Mantoux-positive individual, it can cause an accelerated local reaction (Koch’s phenomenon).

Question 28: Which vaccine utilizes the CYD - TDV strain?

A. HIV vaccine
B. Typhoral
C. Anthrax vaccine
D. Dengavaxia (Correct Answer)

Explanation: **Explanation:** The correct answer is **Dengavaxia**. **Dengavaxia (CYD-TDV)** is the first licensed vaccine for the prevention of Dengue. The name **CYD-TDV** stands for **Chimeric Yellow Fever-Dengue Virus Tetravalent Vaccine**. It is a live-attenuated recombinant vaccine that uses the **Yellow Fever 17D vaccine strain** as a genetic backbone. The structural genes (PrM and E) of the Yellow Fever virus are replaced with those of the four Dengue serotypes (DEN 1, 2, 3, and 4), making it "tetravalent." It is specifically indicated for individuals aged 6–45 years with evidence of prior dengue infection. **Analysis of Incorrect Options:** * **A. HIV Vaccine:** There is currently no licensed HIV vaccine. Experimental candidates like RV144 (Thai trial) use different vectors (Canarypox), not the CYD strain. * **B. Typhoral:** This is the brand name for the **Ty21a** oral vaccine used against *Salmonella typhi*. It is a live-attenuated bacterial vaccine, not a viral chimeric vaccine. * **C. Anthrax Vaccine:** The most common anthrax vaccine is the **Anthrax Vaccine Adsorbed (AVA)**, which is a cell-free filtrate containing the Protective Antigen (PA); it does not involve viral strains. **High-Yield Clinical Pearls for NEET-PG:** * **Dengavaxia Caution:** It should **not** be given to "seronegative" individuals (those never infected with Dengue), as it may increase the risk of severe dengue (Antibody-Dependent Enhancement - ADE) upon subsequent natural infection. * **Schedule:** Administered in 3 doses at 0, 6, and 12-month intervals. * **Other Dengue Vaccines:** Keep an eye on **QDENGA (TAK-003)**, which uses a Dengue serotype 2 backbone instead of Yellow Fever.

Question 29: Nanovalent vaccine offers protection against which types of HPV viruses?

A. 6, 8, 10, 11, 31, 33, 45, 52, 58
B. 6, 11, 16, 18, 31, 33, 45, 52, 58 (Correct Answer)
C. 6, 11, 16, 18, 31, 35, 45, 52, 58
D. 6, 11, 16, 18, 31, 32, 33, 34

Explanation: **Explanation:** The **Nanovalent HPV vaccine (Gardasil 9)** is designed to provide broad protection against Human Papillomavirus (HPV) by targeting nine specific genotypes. These include the four types covered by the quadrivalent vaccine plus five additional high-risk oncogenic types. * **Low-risk types (2):** **6 and 11**, which are responsible for approximately 90% of genital warts (Condyloma acuminata). * **High-risk/Oncogenic types (7):** **16, 18, 31, 33, 45, 52, and 58**. While 16 and 18 cause about 70% of cervical cancers, the addition of the other five types increases protection to approximately 90% of cervical cancer cases. **Analysis of Options:** * **Option B (Correct):** Correctly identifies all nine types (6, 11, 16, 18, 31, 33, 45, 52, 58). * **Option A:** Incorrectly includes types 8 and 10, which are not standard targets for the nanovalent vaccine. * **Option C:** Incorrectly includes type 35 instead of 33. * **Option D:** Incorrectly includes types 32 and 34, which are not part of the Gardasil 9 formulation. **High-Yield Clinical Pearls for NEET-PG:** * **Bivalent Vaccine (Cervarix):** Targets types 16 and 18. * **Quadrivalent Vaccine (Gardasil):** Targets types 6, 11, 16, and 18. * **Mechanism:** These are **subunit vaccines** containing virus-like particles (VLPs) prepared from the L1 capsid protein using recombinant DNA technology. * **Dosage:** For ages 9–14, a 2-dose schedule (0, 6 months) is recommended. For ages 15–45, a 3-dose schedule (0, 2, 6 months) is required. * **Target Population:** Ideally administered before the onset of sexual activity.

Question 30: The '17D' strain is used in the preparation of which vaccine?

A. Oral Polio Vaccine (OPV)
B. Rubella vaccine
C. Chickenpox vaccine
D. Yellow fever vaccine (Correct Answer)

Explanation: **Explanation:** The **17D strain** is a live-attenuated virus strain used specifically for the production of the **Yellow Fever vaccine**. Developed by Max Theiler (who received a Nobel Prize for this work), the 17D strain is derived by serial passage of the wild-type 'Asibi' strain in chicken embryo tissue. It is highly immunogenic and provides long-lasting immunity (often considered lifelong) after a single subcutaneous dose. **Analysis of Incorrect Options:** * **A. Oral Polio Vaccine (OPV):** Uses the **Sabin strains** (Types 1, 2, and 3). These are live-attenuated strains, whereas the Inactivated Polio Vaccine (IPV) uses the Salk (Salk-type) strains like Mahoney. * **B. Rubella Vaccine:** The most commonly used strain globally is the **RA 27/3** strain (isolated from a Rubella Abortus, 27th fetus, 3rd tissue culture). * **C. Chickenpox (Varicella) Vaccine:** Utilizes the **Oka strain**, named after the child from whom the virus was originally isolated. **Clinical Pearls for NEET-PG:** * **Yellow Fever Vaccine:** It is a live-attenuated vaccine. It must be administered at least **10 days** before travel for the International Certificate of Vaccination to be valid. * **Validity:** As per WHO (2016), the certificate of vaccination is now valid for the **life of the person** vaccinated. * **Contraindications:** It is contraindicated in infants <6 months, pregnant women, and immunocompromised individuals (including those with thymus disorders). * **Storage:** It is highly heat-sensitive and must be stored between **+2°C to +8°C**.

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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