Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 471: Measles vaccination is given at -

A. 9 months (Correct Answer)
B. At birth
C. 4 weeks
D. 8 weeks

Explanation: ***9 months*** - The first dose of the **measles vaccine (MMR)** is typically administered at **9 months** of age in many national immunization programs. - This timing is chosen because maternal antibodies, which can interfere with vaccine effectiveness, generally wane by this age. *At birth* - Vaccines given at birth, such as **Hepatitis B** and **BCG**, target diseases with early exposure risks or have efficacy despite maternal antibodies. - Giving measles vaccine at birth would be ineffective due to the presence of **maternal antibodies** that neutralize the vaccine virus. *4 weeks* - This age is generally too early for measles vaccination as significant levels of **maternal antibodies** are often still present, which would reduce the vaccine's efficacy. - Other vaccines, like the rotavirus vaccine, might be given around this age, but not measles. *8 weeks* - While maternal antibodies might be decreasing, 8 weeks of age is still generally considered too early for optimal measles vaccine response. - Many primary vaccine series (e.g., DTaP, IPV, Hib) begin at 6-8 weeks, but measles is usually delayed further for better efficacy and seroconversion rates.

Question 472: Which vaccine is used to prevent cholera?

A. CVD 103-HgR
B. Ty21 A
C. WC-rBS (Correct Answer)
D. None of the options

Explanation: ***WC-rBS*** * **WC-rBS** stands for **whole-cell, recombinant B subunit** vaccine, also known as **Dukoral**. * It is an **oral inactivated vaccine** containing killed *Vibrio cholerae* O1 bacteria and the recombinant B subunit of the cholera toxin, providing immunity against cholera. * **WC-rBS is the WHO-prequalified cholera vaccine** widely used in India and recommended for travellers and in epidemic settings. * It provides protection against both O1 and O139 serogroups and offers some cross-protection against ETEC (enterotoxigenic *E. coli*). *CVD 103-HgR* * **CVD 103-HgR** (commercially known as **Vaxchora**) is an **oral live-attenuated cholera vaccine** approved by the FDA. * It is a genetically modified *Vibrio cholerae* O1 Inaba strain with deleted cholera toxin genes. * While this is also a cholera vaccine, **it is primarily used in the United States** and is not the standard vaccine used in India or recommended by WHO for mass vaccination campaigns. * In the Indian context and for NEET-PG examinations, **WC-rBS (Dukoral) is the recognized cholera vaccine**. *Ty21a* * **Ty21a** is an **oral live-attenuated vaccine** used to prevent **typhoid fever**. * It is specifically designed to target *Salmonella Typhi* bacteria, not *Vibrio cholerae*. *None of the options* * This option is incorrect because WC-rBS is the well-established and WHO-recommended vaccine for the prevention of cholera in the Indian context.

Question 473: What are the serogroups covered by the bivalent meningococcal vaccine?

A. Serogroup A
B. Serogroup A and C (Correct Answer)
C. Serogroup W
D. Serogroup C

Explanation: ***Serogroup A and C*** - The **bivalent meningococcal vaccine** specifically targets and provides protection against **Neisseria meningitidis** serogroups **A and C**. - This vaccine is crucial for preventing invasive meningococcal disease caused by these prevalent strains, particularly in the African meningitis belt. - Examples include **meningococcal AC conjugate vaccines** used in mass vaccination campaigns. *Serogroup A* - While **Serogroup A** is one of the types covered by bivalent vaccines, it is not the only one. - A vaccine covering only Serogroup A would be a **monovalent vaccine**, not bivalent. *Serogroup W* - **Serogroup W** is covered by **quadrivalent meningococcal vaccines** (e.g., MenACWY) which protect against serogroups A, C, W, and Y. - It is **not included** in **bivalent** formulations. *Serogroup C* - While **Serogroup C** is one of the types covered by bivalent vaccines, it is not the only one. - A vaccine covering only Serogroup C would be a **monovalent vaccine**, not bivalent.

Question 474: At what age can the measles vaccine be administered for the first time in high-risk scenarios or outbreak situations?

A. 3 to 5 months
B. 5 to 6 months
C. At 6 months (Correct Answer)
D. Before 3 months

Explanation: ***At 6 months*** - In situations of **high risk** or **outbreaks**, the measles vaccine can be given as early as **6 months of age**. - This early dose is considered an extra dose and does not count towards the routine vaccination schedule; a child would still need to receive the standard doses at 12-15 months and 4-6 years. *3 to 5 months* - The measles vaccine is generally not recommended before **6 months of age** because the presence of **maternal antibodies** can interfere with the vaccine's effectiveness. - Vaccinating at this age would likely result in an inadequate immune response. *5 to 6 months* - While closer to the recommended age for high-risk situations, the consensus for early vaccination due to high risk or outbreak remains at **6 months of age**. - Administering it slightly before 6 months may still face issues with **maternal antibody interference**, potentially reducing efficacy. *Before 3 months* - Vaccinating this early is not recommended due to significant interference from **maternal antibodies**, which are still abundant in infants. - The infant's **immune system** is also less mature, leading to an even weaker response and decreased protection.

Question 475: What is the concentration of type 3 virus in the trivalent oral polio vaccine?

A. 400,000 TCID 50
B. 100,000 TCID 50
C. 300,000 TCID 50
D. 600,000 TCID 50 (Correct Answer)

Explanation: ***600,000 TCID 50*** - The **trivalent oral polio vaccine (tOPV)** traditionally contained specific concentrations of each serotype: **type 1 (1,000,000 TCID50/dose)**, **type 2 (100,000 TCID50/dose)**, and **type 3 (600,000 TCID50/dose)**. - Type 3 poliovirus requires a **higher concentration (600,000 TCID50)** compared to type 2 to achieve adequate immunogenicity and protection. - The **World Health Organization (WHO)** established these specific formulations for tOPV to ensure optimal efficacy and safety for each serotype. *100,000 TCID 50* - This is the concentration of **type 2 poliovirus** in tOPV, not type 3. - Due to the **global eradication of wild poliovirus type 2** by 2015, tOPV was replaced with bivalent OPV (bOPV) containing only types 1 and 3 in routine immunization programs. *400,000 TCID 50* - This concentration does not correspond to any standard poliovirus serotype in the traditional trivalent oral polio vaccine. - This value falls between type 2 (100,000) and type 3 (600,000) concentrations but is not used. *300,000 TCID 50* - This concentration is not the standard for any poliovirus serotype in the traditional trivalent oral polio vaccine. - Each serotype has a **distinct, empirically determined concentration** to achieve optimal immunity while minimizing adverse effects.

Question 476: In which of the following diseases is mass vaccination considered ineffective?

A. Tetanus (Correct Answer)
B. None of the options
C. Measles
D. Polio

Explanation: ***Correct: Tetanus*** - Mass vaccination is considered **ineffective** for tetanus because it is **not a communicable disease** transmitted person-to-person - Tetanus is caused by **Clostridium tetani** spores present in soil and environment - Since there is **no herd immunity** benefit, vaccinating large populations simultaneously does not break any chain of transmission - **Individual immunization** with tetanus toxoid is highly effective for personal protection, but this is different from mass vaccination strategies used for communicable diseases - The focus for tetanus prevention is on **universal immunization** and **wound management**, not mass campaigns *Incorrect: Measles* - Mass vaccination for measles is **highly effective** due to its person-to-person transmission - Achieving high vaccination coverage (>95%) provides **herd immunity** and can lead to **elimination** - The **MMR vaccine** is a cornerstone of mass immunization programs worldwide *Incorrect: Polio* - Mass vaccination campaigns (Pulse Polio) have been **extremely effective** in nearly eradicating polio globally - The disease spreads through the fecal-oral route, making mass vaccination crucial for breaking transmission chains - Both **OPV** and **IPV** provide individual and community protection through herd immunity *Incorrect: None of the options* - This is incorrect because tetanus is a clear example where mass vaccination strategy is ineffective due to lack of person-to-person transmission

Question 477: What is the minimum percentage of the population that needs to be vaccinated to eradicate measles?

A. 85%
B. 95% (Correct Answer)
C. 70%
D. 80%

Explanation: **95%** - Measles is highly contagious, requiring a **high percentage of immunity** in the population to establish **herd immunity** and prevent outbreaks. - A **95% vaccination coverage** ensures that enough individuals are protected, breaking the chain of transmission and leading to potential eradication. *85%* - This percentage is **insufficient** for highly transmissible diseases like measles. - An 85% vaccination rate would still leave a significant portion of the population susceptible, allowing measles to **continue circulating** and causing outbreaks. *70%* - This level of vaccination is **far too low** for measles, which has a basic reproduction number (R0) of 12-18. - A 70% coverage would result in frequent and widespread measles outbreaks due to **inadequate herd immunity**. *80%* - While 80% vaccination offers some protection, it is still **below the threshold** needed for measles eradication. - Measles outbreaks can still occur with an 80% coverage, particularly in populations with **non-uniform distribution of immunity**.

Question 478: In a contaminated, punctured wound of the leg of a non-immune child of 10, which one of the following measures would provide the best protection against the development of tetanus?

A. Active immunization and antibiotics
B. Active immunization, wound excision and primary closure
C. Active and passive immunization along with antibiotics (Correct Answer)
D. Active immunization, antibiotics and immobilisation

Explanation: ***Active and passive immunization along with antibiotics*** - For a non-immune child with a **contaminated, punctured wound** (tetanus-prone wound), immediate protection is critical since *Clostridium tetani* spores may already be present. - **Passive immunization** (Tetanus Immunoglobulin/TIG) provides immediate antibodies to neutralize tetanus toxin (immediate protection). - **Active immunization** (Tetanus Toxoid/TT) initiates the body's own antibody production for long-term immunity (takes 2-4 weeks). - **Antibiotics** (metronidazole or penicillin) help eliminate C. tetani and prevent secondary bacterial infections. - This combination approach is the **standard WHO/CDC guideline** for tetanus prophylaxis in non-immune individuals with high-risk wounds. *Active immunization and antibiotics* - **Active immunization alone** takes 2-4 weeks to generate protective antibodies and provides **no immediate protection** against tetanus in a non-immune individual. - A non-immune child with a contaminated wound needs **immediate passive immunity** (TIG) since the incubation period of tetanus can be as short as 3-21 days. - Antibiotics alone cannot neutralize pre-formed tetanus toxin. *Active immunization, antibiotics and immobilisation* - **Immobilization** is a supportive measure for fractures or severe soft tissue injuries, but has **no role in tetanus prevention**. - This option lacks **passive immunization (TIG)**, which is absolutely essential for immediate protection in a non-immune individual with a tetanus-prone wound. *Active immunization, wound excision and primary closure* - **Wound debridement/excision** to remove contaminated and devitalized tissue is important for wound management. - However, **primary closure of a contaminated, punctured wound is contraindicated** as it creates an anaerobic environment that favors *Clostridium tetani* spore germination and toxin production. - Contaminated wounds should be left open or undergo delayed primary closure after ensuring the wound is clean. - This option critically omits **passive immunization (TIG)**, making it inadequate for tetanus prevention in a non-immune child.

Question 479: Which of the following diseases currently lacks a widely available effective vaccine?

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

Explanation: ***Dengue fever*** - While there is a vaccine (Dengvaxia) available in some regions for specific populations, its use is restricted due to concerns about increased risk of severe dengue in **seronegative individuals**. - There is currently **no single, universally recommended, and widely available effective vaccine** for all populations against all serotypes of dengue, making dengue a disease greatly in need of better vaccination strategies. *Yellow fever* - A **highly effective and safe live-attenuated vaccine** against yellow fever has been available for many decades, providing long-lasting immunity. - It is a standard vaccine for travelers to endemic areas and part of routine immunization programs in many affected countries. *Japanese encephalitis* - Several effective vaccines against Japanese encephalitis are **widely available and recommended** for individuals living in or traveling to endemic regions. - These vaccines include inactivated and live-attenuated forms, offering significant protection against the disease. *Russian spring summer encephalitis* - An **effective inactivated vaccine** is available for Russian spring-summer encephalitis and is recommended for those at risk due to occupational exposure or travel to endemic areas. - Vaccination provides reliable protection against this tick-borne viral infection.

Question 480: Which of the following vaccines is NOT included in the National Immunization Schedule?

A. TT
B. OPV
C. Measles
D. Human Papillomavirus (HPV) (Correct Answer)

Explanation: ***Human Papillomavirus (HPV)*** - **HPV vaccine is NOT part of India's routine Universal Immunization Programme (UIP)**, making it the correct answer. - While **pilot programs** have been conducted in some states and various bodies recommend it, HPV has **never been universally included** in India's national immunization schedule. *TT (Tetanus Toxoid)* - **TT is a core component** of India's UIP and is actively used in immunization programs. - Given to **pregnant women** (2 doses during pregnancy) and as **Td vaccine** at 10 and 16 years of age. *OPV (Oral Polio Vaccine)* - While **OPV was phased out** from India's UIP in 2016, it was **historically part** of the national schedule. - India switched to **Injectable Polio Vaccine (IPV)** to eliminate vaccine-derived polio risk, but OPV was previously included. *Measles* - **Measles vaccine is actively included** in India's UIP as part of the **MR (Measles-Rubella) vaccine**. - Administered at **9 months and 16-24 months** of age as part of routine immunization.

Practice by Chapter

Principles of Immunization

Practice Questions

Types of Vaccines

Practice Questions

Universal Immunization Program

Practice Questions

Cold Chain System

Practice Questions

Vaccine Storage and Handling

Practice Questions

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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