Immunization and Vaccine-Preventable Diseases Practice Questions

Q: What is true about the mumps vaccine?

It has an efficacy of 95%.. **Explanation:** **Correct Option (B): It has an efficacy of 95%.** The mumps vaccine contains the live-attenuated **Jeryl Lynn strain** (most common globally). A single dose provides approximately 80% protection, but after the recommended **two-dose schedule**, the vaccine efficacy increases to about **95%**. This high level of seroconversion is essential for maintaining herd immunity and preventing outbreaks in congregate settings. **Analysis of Incorrect Options:** * **A. It is a killed vaccine:** This is incorrect. The mumps vaccine is a **Live Attenuated Viral Vaccine**. Like most viral vaccines in the routine schedule (except IPV and Hepatitis B), it uses a weakened form of the virus to induce a robust immune response. * **C. Only one dose is administered:** Incorrect. Under the current Universal Immunization Programme (UIP) and IAP guidelines, **two doses** are recommended (usually as MMR/MR) at 9 months and 16–24 months to ensure long-term immunity. * **D. It is not combined with other vaccines:** Incorrect. It is almost always administered as part of a combination vaccine, such as **MMR** (Measles, Mumps, Rubella) or **MMRV** (adding Varicella). **High-Yield Clinical Pearls for NEET-PG:** * **Strain:** The Jeryl Lynn strain is the gold standard; other strains include Urabe (linked to higher rates of aseptic meningitis) and Leningrad-3. * **Storage:** It is heat-sensitive and must be stored at **+2°C to +8°C** (Cold Chain). * **Contraindication:** Being a live vaccine, it is contraindicated in **pregnancy** and **severely immunocompromised** individuals. * **Complication:** While the vaccine is safe, the most common complication of the *disease* itself in post-pubertal males is **orchitis** (usually unilateral).

Q: An OPV vial shows a specific symbol. What does this symbol indicate?

Use the vaccine if the expiry date has not been reached. ***Use the vaccine if the expiry date has not been reached*** - This describes **VVM Stage 1**, where the **inner square is lighter** than the outer circle, indicating the vaccine can be safely used if within the expiry date. - The **Vaccine Vial Monitor (VVM)** at this stage shows minimal heat exposure and maintains vaccine potency. *The vaccine has reached its expiry date* - **VVM symbols** indicate **heat exposure**, not expiry dates - expiry dates are printed separately on the vial label. - Even if VVM shows Stage 1 (usable), an expired vaccine should never be administered regardless of the VVM reading. *The vaccine has not been stored properly* - **VVM Stage 1** actually indicates **proper cold chain maintenance** with minimal cumulative heat exposure. - Improper storage would show **VVM Stage 3 or 4**, where the inner square becomes equal to or darker than the outer circle. *The vaccine vial is empty* - **VVM symbols** monitor **heat exposure and vaccine potency**, not the physical quantity of vaccine in the vial. - An empty vial would be visually apparent and does not require a specific symbol to indicate.

Q: To eradicate measles, what percentage of the population needs to be vaccinated?

95%. To achieve the eradication of measles, a herd immunity threshold of **95%** is required. This high threshold is dictated by the basic reproduction number ($R_0$) of the measles virus, which is one of the most contagious pathogens known to humans (each infected person can spread the virus to 12–18 susceptible individuals). ### Why 95% is Correct The formula for herd immunity threshold is $H = 1 - (1/R_0)$. Given that measles has an $R_0$ of 12–18, the mathematical requirement for stopping transmission is approximately 92–95%. Because the measles vaccine (Edmonston-Zagreb strain) is highly effective but not 100% protective in a single dose, a 95% coverage rate with two doses is the global standard set by the WHO to ensure the virus cannot find enough susceptible hosts to sustain an outbreak. ### Analysis of Incorrect Options * **70% (Option A):** This is the threshold for diseases with lower $R_0$ values, such as Diphtheria or Polio. * **80% (Option B):** This level of coverage may reduce the number of cases but is insufficient to prevent periodic outbreaks of measles. * **85% (Option C):** While this is the target for many routine immunizations, it falls short for measles, leading to "immunity gaps" that allow the virus to circulate. ### High-Yield NEET-PG Pearls * **Measles Eradication vs. Elimination:** Eradication is global; elimination is regional. India currently aims for Measles-Rubella (MR) elimination. * **Vaccine Type:** Live attenuated vaccine. * **Dose Schedule:** 1st dose at 9 completed months; 2nd dose at 16–24 months. * **Outbreak Definition:** Even a single laboratory-confirmed case of measles is considered an outbreak in a community. * **Vitamin A:** Administered alongside the vaccine to reduce morbidity and mortality.

Q: The 23-valent pneumococcal polysaccharide vaccine is recommended in all of the following conditions except?

Children less than 2 years of age. ### Explanation The **23-valent Pneumococcal Polysaccharide Vaccine (PPSV23)** contains purified capsular polysaccharides. The core immunological principle here is that polysaccharide antigens are **T-cell independent**. **1. Why Option C is correct:** In children **less than 2 years of age**, the immune system (specifically the splenic marginal zone) is immature and cannot mount an effective immune response to T-cell independent antigens. Therefore, PPSV23 is **ineffective and not recommended** in this age group. For children under 2, the **Pneumococcal Conjugate Vaccine (PCV)** is used instead, as it attaches the polysaccharide to a protein carrier, making it T-cell dependent and immunogenic in infants. **2. Analysis of Incorrect Options:** PPSV23 is indicated for "high-risk" individuals aged 2 years and older who are at increased risk of invasive pneumococcal disease (IPD): * **Option A (CSF Leak):** This is a high-risk condition as it provides a direct pathway for bacteria to cause meningitis. * **Option B (Chronic Cardiac Disease):** Conditions like congestive heart failure or cardiomyopathies increase vulnerability to severe pneumonia. * **Option D (Nephrotic Syndrome):** This is an immunocompromised state characterized by the loss of antibodies and complement factors in urine, significantly increasing the risk of pneumococcal infection. **High-Yield Clinical Pearls for NEET-PG:** * **PCV (e.g., PCV13):** Given in the National Immunization Schedule at 6 weeks, 14 weeks, and a booster at 9 months. * **PPSV23:** Does not produce mucosal immunity or herd immunity and does not induce immunological memory (unlike PCV). * **Sequential Vaccination:** In high-risk adults, PCV is often given first, followed by PPSV23 after an interval (usually 8 weeks to 1 year) to broaden serotype coverage. * **Asplenia/Sickle Cell Anemia:** These are the highest-yield indications for PPSV23 in patients >2 years old.

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

30 days. **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**.

Q: Which of the following vaccines is recommended for newborns?

BCG. **Explanation:** In accordance with the National Immunization Schedule (NIS) in India, the vaccines administered at birth (birth dose) are **BCG, Oral Polio Vaccine (OPV-0), and Hepatitis B**. **Why BCG is the correct answer:** BCG (Bacillus Calmette-Guérin) is a live attenuated vaccine derived from *Mycobacterium bovis*. It is administered intradermally (0.05 ml for newborns) to protect against severe forms of childhood tuberculosis, such as TB meningitis and disseminated (miliary) TB. It is recommended as soon as possible after birth. **Why the other options are incorrect:** * **MMR (Measles, Mumps, Rubella):** This is a live vaccine typically administered at 9 months (as MR) or 12–15 months. It is not given at birth due to the presence of maternal antibodies, which can interfere with the immune response. * **DPT (Diphtheria, Pertussis, Tetanus):** The primary series for DPT (usually as part of the Pentavalent vaccine) starts at 6 weeks of age, followed by doses at 10 and 14 weeks. * **HiB (Haemophilus influenzae type b):** This is also part of the Pentavalent vaccine and is initiated at 6 weeks of age, not at birth. **High-Yield Clinical Pearls for NEET-PG:** * **BCG Site:** Left upper arm (deltoid) to maintain uniformity for scar inspection. * **BCG Evolution:** Papule (2-3 weeks) → Pustule → Shallow Ulcer → Permanent depressed scar (6-12 weeks). * **Dose Change:** If not given at birth, the dose is 0.1 ml after 1 month of age. It can be given up to 1 year of age. * **Hepatitis B:** The birth dose must be given within 24 hours to prevent vertical transmission.

Q: Which vaccine strain needs to be changed every year?

Influenza. **Explanation:** The correct answer is **Influenza** because of the unique genetic characteristics of the Influenza virus, specifically **Antigenic Drift**. **1. Why Influenza?** Influenza viruses (Type A and B) undergo frequent point mutations in the genes coding for surface glycoproteins, **Hemagglutinin (HA)** and **Neuraminidase (NA)**. This process, known as *Antigenic Drift*, results in new virus strains that can evade the immune system of individuals previously infected or vaccinated. Consequently, the World Health Organization (WHO) monitors global circulation and updates the vaccine composition annually (Northern and Southern Hemisphere strains) to ensure a close antigenic match. **2. Why the other options are incorrect:** * **Measles & Mumps:** These are caused by viruses that are antigenically stable. The surface antigens do not undergo significant mutations over time, meaning the immunity conferred by the standard MMR vaccine remains effective for decades. * **Polio:** The three serotypes of Poliovirus (1, 2, and 3) are stable. While the world has switched from Trivalent to Bivalent OPV (removing Type 2), the strains themselves do not require annual updates. **High-Yield Clinical Pearls for NEET-PG:** * **Antigenic Drift:** Seen in both Influenza A and B; leads to **epidemics**. * **Antigenic Shift:** Seen **only in Influenza A**; involves genetic reassortment leading to a major change (new subtype); leads to **pandemics**. * **Vaccine Timing:** In India, it is ideally administered before the monsoon season. * **Composition:** Most modern vaccines are **Quadrivalent** (2 strains of Influenza A and 2 lineages of Influenza B).

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

Yellow fever. **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 1

What is true about the mumps vaccine?

Accepted Answer

It has an efficacy of 95%.

Answer

It is a killed vaccine.

Answer

Only one dose is administered.

Answer

It is not combined with other vaccines.

Question 2

Which of the following is NOT a strategy for measles elimination?

Accepted Answer

Mop up: Vaccinate children missed during routine vaccination.

Answer

Catch up: One-time nationwide vaccination of children aged 9 months to 14 years.

Answer

Keep up: Vaccinate over 95% in successive birth cohorts.

Answer

Follow up: Nationwide vaccination every 2-4 years.

Question 3

An OPV vial shows a specific symbol. What does this symbol indicate?

Accepted Answer

Use the vaccine if the expiry date has not been reached

Answer

The vaccine has reached its expiry date

Answer

The vaccine has not been stored properly

Answer

The vaccine vial is empty

Question 4

To eradicate measles, what percentage of the population needs to be vaccinated?

Accepted Answer

95%

Answer

70%

Answer

80%

Answer

85%

Question 5

The 23-valent pneumococcal polysaccharide vaccine is recommended in all of the following conditions except?

Accepted Answer

Children less than 2 years of age

Answer

Cerebrospinal fluid leak

Answer

Chronic cardiac disease

Answer

Nephrotic syndrome

Question 6

Which of the following statements is true about the pneumococcal vaccine?

Accepted Answer

It is not given in splenectomy patients.

Answer

It is not given if the age is less than 2 years.

Answer

It is polyvalent.

Answer

It is derived from capsular protein.

Question 7

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

Accepted Answer

30 days

Answer

7 days

Answer

10 days

Answer

21 days

Question 8

Which of the following vaccines is recommended for newborns?

Accepted Answer

BCG

Answer

MMR

Answer

DPT

Answer

HiB

Question 9

Which vaccine strain needs to be changed every year?

Accepted Answer

Influenza

Answer

Measles

Answer

Mumps

Answer

Polio

Question 10

Which of the following vaccinations is absolutely contraindicated in pregnancy?

Accepted Answer

Yellow fever

Answer

Hepatitis-B

Answer

Cholera

Answer

Rabies

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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