Immunization and Vaccine-Preventable Diseases Practice Questions

Q: Which is the best way to prevent the spread of Polio during an epidemic?

Oral Polio Vaccine (OPV) to all children. **Explanation:** The primary goal during a polio epidemic is to rapidly break the chain of transmission and induce "herd immunity." **Oral Polio Vaccine (OPV)** is the intervention of choice for the following reasons: 1. **Intestinal Immunity:** OPV (Sabin) is a live-attenuated vaccine that induces robust local secretory IgA production in the gut. Since Poliovirus is transmitted via the feto-oral route, this intestinal barrier prevents the wild virus from multiplying and being excreted, effectively stopping community spread. 2. **Secondary Spread:** Vaccinated individuals shed the vaccine virus in their stools, which can "immunize" unvaccinated contacts in areas with poor sanitation (contact immunity). 3. **Rapid Response:** OPV is easy to administer on a mass scale without the need for trained healthcare workers or sterile equipment. **Analysis of Incorrect Options:** * **B. Isolation:** Polio has a high ratio of inapparent (asymptomatic) infections to clinical cases (approx. 1:200 for Type 1). For every one clinical case isolated, hundreds of silent carriers continue to spread the virus, making isolation ineffective for outbreak control. * **C. IPV:** While IPV (Salk) provides excellent individual protection by inducing systemic IgG (preventing paralytic polio), it does **not** produce significant intestinal immunity. An IPV-vaccinated child can still be infected with wild poliovirus and shed it in their feces, failing to stop an epidemic. **NEET-PG High-Yield Pearls:** * **Vaccine of Choice in Epidemics:** OPV (due to rapid gut immunity). * **Vaccine for Routine Immunization (India):** bOPV (Type 1 & 3) + fIPV (Fractional Inactivated Polio Vaccine). * **Most Heat Sensitive Vaccine:** OPV (requires storage at -20°C; monitored by Vaccine Vial Monitor - VVM). * **Herd Immunity:** OPV contributes to herd immunity; IPV does not.

Q: What is true regarding measles outbreaks?

Vaccination is given at 6 months. **Explanation:** The correct answer is **C: Vaccination is given at 6 months.** While the routine Measles-Rubella (MR) vaccine is scheduled at 9 months, the WHO and National Guidelines state that during a **measles outbreak**, a "supplementary dose" or "outbreak response immunization" can be administered as early as **6 months of age**. This dose is considered "extra" and does not count towards the routine schedule. **Analysis of Options:** * **A: Proportion of susceptible children:** An outbreak typically occurs when the proportion of susceptible children in a population exceeds **10%**, not 20%. Maintaining herd immunity requires >90-95% coverage. * **B: Virgin Community:** In a "virgin community" (where the virus has never been introduced), measles is highly infectious, typically affecting **nearly 100%** of the susceptible population, not 50%. * **D: Periodicity:** In the pre-vaccination era, measles epidemics occurred in cycles every **2–3 years**, not 6–7 years. Vaccination has significantly altered this periodicity. **High-Yield Clinical Pearls for NEET-PG:** * **Infectivity:** Measles is most infectious during the **prodromal/catarrhal stage** (before the rash appears). * **Secondary Attack Rate (SAR):** It has a very high SAR of **>80%** among susceptible household contacts. * **Vitamin A:** Regardless of the previous dose, two doses of Vitamin A (24 hours apart) are mandatory for all children diagnosed with measles to prevent complications like blindness and pneumonia. * **Isolation:** Cases should be isolated for **4 days after the appearance of the rash**.

Q: In the Rabies vaccine schedule of 0, 3, 7, 14, 30, 90 days, what does the '0' represent?

Day of first injection. **Explanation:** In the context of Post-Exposure Prophylaxis (PEP) for Rabies, the schedule (0, 3, 7, 14, 28/30, and optional 90 days) refers to the timing of vaccine administration. **Day '0' represents the day the first dose of the vaccine is administered**, not the day of the bite itself. This is a critical distinction because patients may present to a clinic several days after the actual exposure. **Analysis of Options:** * **Day of first injection (Correct):** Medical protocols define Day 0 as the initiation of treatment. All subsequent doses (Day 3, 7, etc.) are calculated based on this first visit to ensure the correct immunological interval for antibody production. * **Day of dog bite:** While ideally the vaccine is started on the day of the bite, Day 0 specifically marks the start of the medical intervention. If a patient presents 3 days after a bite, that day becomes their "Day 0." * **Day of symptom onset:** Rabies is 100% fatal once clinical symptoms appear. Vaccination is a preventive measure; once symptoms start, the vaccine is no longer effective. * **Day of dog death:** The 10-day observation period of the animal is used to decide whether to *continue* or *stop* the vaccine series, but it does not define the start date of the schedule. **High-Yield Clinical Pearls for NEET-PG:** * **Essen Schedule:** The 5-dose Intramuscular (IM) regimen (0, 3, 7, 14, 28). The 90th-day dose is now considered optional/historical. * **Updated Thai Red Cross Schedule (IDRV):** The current WHO-recommended intradermal regimen is **2-2-2** (2 doses on days 0, 3, and 7). * **Site of Injection:** Deltoid muscle in adults; anterolateral thigh in children. **Never** in the gluteal region (reduced immunogenicity due to fat). * **Category III Bites:** Require both Rabies Vaccine and Rabies Immunoglobulin (RIG) on Day 0.

Q: A baby is brought for immunization for the first time at 18 months of age. Which vaccine(s) can be administered?

DPT booster and OPV. ### Explanation The core concept here is the **upper age limit** for specific vaccines under the National Immunization Schedule (NIS) in India. **1. Why Option B is Correct:** At 18 months, the child has crossed the age limit for the primary series of the Pentavalent vaccine (which must be completed by 12 months). According to the NIS, if a child presents late (between 1–7 years) and is unimmunized, we initiate the **DPT booster** (as the primary dose) and **OPV**. Since the child is 18 months old, they fall perfectly into the window for the first DPT booster (16–24 months) and the OPV booster. **2. Why the other options are incorrect:** * **Option A (Pentavalent):** The Pentavalent vaccine (DPT + Hep B + Hib) has a strict upper age limit of **12 months**. Beyond one year, the Hepatitis B and Hib components are generally not administered in the routine public health schedule. * **Option C (Pentavalent, OPV, DPT, Measles, Mumps):** This is incorrect because Pentavalent cannot be given after 1 year. Additionally, the NIS uses the **MR (Measles-Rubella)** vaccine, not the Mumps vaccine. * **Option D (BCG plus OPV):** The upper age limit for the **BCG vaccine is 1 year**. If a child is older than 12 months, BCG is no longer administered as per the National Guidelines. **3. High-Yield Clinical Pearls for NEET-PG:** * **BCG:** Limit is 1 year. (Dose: 0.05ml until 1 month; 0.1ml thereafter). * **Pentavalent/Rotavirus/Fractional IPV:** Limit is 1 year. * **Measles/MR:** Can be given up to 5 years of age. * **DPT:** Can be given up to 7 years of age. (Beyond 7 years, use Td). * **OPV:** Can be given up to 5 years of age. * **Vitamin A:** Can be given up to 5 years of age.

Q: Which of the following vaccines can be used in pregnancy in normal circumstances?

Influenza trivalent vaccine. **Explanation:** The fundamental principle of immunization during pregnancy is the avoidance of **Live Attenuated Vaccines** due to the theoretical risk of the vaccine virus crossing the placenta and causing fetal infection or congenital anomalies. **Why Influenza Trivalent Vaccine is Correct:** The **Inactivated Influenza Vaccine (IIV)** is a killed vaccine and is highly recommended for all pregnant women during any trimester. Pregnancy increases the risk of severe complications from influenza (like pneumonia) due to physiological changes in the respiratory and immune systems. Vaccination not only protects the mother but also provides passive immunity to the newborn via transplacental antibody transfer, protecting the infant during the first six months of life. **Analysis of Incorrect Options:** * **MMR (Measles, Mumps, Rubella):** This is a live attenuated vaccine. Rubella components, in particular, pose a risk of Congenital Rubella Syndrome (CRS). It is contraindicated in pregnancy, and women are advised to avoid conception for 4 weeks after receiving it. * **Varicella Vaccine:** This is a live attenuated vaccine. It is contraindicated due to the theoretical risk of Congenital Varicella Syndrome. * **Hepatitis A Vaccine:** While it is an inactivated vaccine, it is not used in "normal circumstances." It is only indicated in pregnancy if there is a high risk of exposure or underlying chronic liver disease. **High-Yield Clinical Pearls for NEET-PG:** * **Safe in Pregnancy:** Tdap (Tetanus, Diphtheria, Pertussis), Inactivated Influenza, and Hepatitis B (if indicated). * **Contraindicated:** MMR, Varicella, Yellow Fever, Oral Polio (OPV), and BCG. * **Tetanus Toxoid (TT/Td):** The most common vaccine administered in pregnancy to prevent Neonatal Tetanus. * **Rule of Thumb:** Killed/Inactivated vaccines and Toxoids are generally safe; Live vaccines are contraindicated.

Q: What is the recommended dose of Rabies immunoglobulin?

20 IU/kg body weight. **Explanation:** The correct answer is **C. 20 IU/kg body weight**. **1. Why the correct answer is right:** Rabies Immunoglobulin (RIG) provides immediate **passive immunity** by neutralizing the rabies virus at the wound site before the patient’s own immune system can produce antibodies via vaccination (active immunity). The standard dose for **Human Rabies Immunoglobulin (HRIG)** is **20 IU/kg body weight**. It is administered as a one-time dose, ideally on Day 0, by infiltrating as much as possible into and around the wound(s). **2. Why the incorrect options are wrong:** * **A & B (10-15 IU/kg):** These doses are sub-therapeutic and would not provide sufficient neutralizing antibodies to prevent the virus from entering the peripheral nerves. * **D (25 IU/kg):** This exceeds the standard HRIG dose. However, it is important to note that if **Equine Rabies Immunoglobulin (ERIG)** is used instead of HRIG, the dose is **40 IU/kg body weight** (double the HRIG dose) due to its lower potency and faster clearance. **3. High-Yield Clinical Pearls for NEET-PG:** * **Site of Injection:** RIG should be infiltrated **locally** into the wound. Any remaining volume should be injected intramuscularly at a site distant from the vaccine injection. * **Timing:** RIG is indicated for **Category III bites** (and Category II in immunocompromised patients). It can be given up to **7 days** after the first dose of the vaccine; beyond 7 days, it is not recommended as the body starts producing its own antibodies. * **Never exceed the dose:** Excessive RIG can interfere with the active immune response generated by the rabies vaccine. * **No RIG for previously immunized:** If a patient has a documented history of complete Pre-exposure or Post-exposure prophylaxis, RIG is **not** required during re-exposure.

Q: Which of the following vaccines has maximum efficacy after a single dose?

Measles. **Explanation:** The efficacy of a vaccine refers to the percentage reduction in disease incidence among vaccinated persons compared to unvaccinated ones. **Why Measles is the Correct Answer:** Measles is a **Live Attenuated Vaccine**. Live vaccines generally mimic a natural infection, leading to robust humoral and cell-mediated immunity. A single dose of the Measles vaccine (given at 9 months in India) has an exceptionally high seroconversion rate of approximately **85–95%**. Because it is highly immunogenic, a single dose is sufficient to provide long-lasting protection in the majority of the population, making its single-dose efficacy superior to the other options listed. **Analysis of Incorrect Options:** * **Tetanus Toxoid (TT) & DPT:** These are **Toxoid/Killed vaccines**. Inactivated vaccines are generally less immunogenic than live vaccines. They require a primary series (multiple doses) followed by periodic boosters to achieve and maintain protective antibody titers. A single dose of TT or DPT provides negligible long-term protection. * **Typhoid:** Whether using the polysaccharide (Vi) or the conjugate vaccine, the efficacy of a single dose is lower (approx. 60–70% for Vi) compared to Measles, and the immunity tends to wane over 2–3 years, requiring revaccination. **High-Yield Clinical Pearls for NEET-PG:** * **Maximum Efficacy:** Measles (~95%) > BCG (0–80%, highly variable). * **Cold Chain:** Measles vaccine is highly heat-sensitive and must be reconstituted only with the provided diluent. Once reconstituted, it must be used within **4 hours**. * **Zero Dose:** In the context of Polio, the "Zero Dose" refers to the dose given at birth to induce local intestinal immunity. * **Most Heat Sensitive Vaccine:** Oral Polio Vaccine (OPV). * **Most Heat Resistant Vaccine:** Tetanus Toxoid (TT).

Q: How often are booster doses recommended for the ViPS vaccine?

Every 3 years. **Explanation:** The **ViPS (Vi Polysaccharide) vaccine** is a parenteral (injectable) subunit vaccine used for protection against Typhoid fever. It contains the purified Vi capsular polysaccharide antigen of *Salmonella typhi*. **1. Why Option C is Correct:** The ViPS vaccine is T-cell independent. Because it is a pure polysaccharide vaccine, it does not induce immunological memory. Antibody levels (specifically IgG) elicited by the vaccine decline significantly over time, and the protective efficacy drops below threshold levels after a few years. Therefore, to maintain protective immunity, a **booster dose is required every 3 years**. It is recommended for individuals aged 2 years and older. **2. Why Other Options are Incorrect:** * **Option A (Every year):** Annual boosters are unnecessary as the protective antibody levels generally persist for at least 2–3 years. * **Option B (Every 2 years):** While some older guidelines suggested frequent dosing, the standard WHO and National guidelines for ViPS specify a 3-year interval. * **Option D (Every 4 years):** By the fourth year, the efficacy of the polysaccharide vaccine significantly wanes, leaving the individual susceptible to infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Typhoid Conjugate Vaccine (TCV):** Unlike ViPS, TCV (e.g., Typbar-TCV) is conjugated to a protein carrier (Tetanus Toxoid). This makes it T-cell dependent, providing longer-lasting immunity, and it can be given as early as **6 months of age**. * **Oral Ty21a Vaccine:** A live attenuated vaccine given in a 3-dose schedule (Days 1, 3, and 5). It requires a booster every **3 to 5 years**. * **Minimum Age:** ViPS cannot be given to children **under 2 years** because their immune systems do not respond well to polysaccharide antigens.

Question 1

Which is the best way to prevent the spread of Polio during an epidemic?

Accepted Answer

Oral Polio Vaccine (OPV) to all children

Answer

Isolation of the infected individuals

Answer

Inactivated Polio Vaccine (IPV) to children

Answer

None of the above

Question 2

What is true regarding measles outbreaks?

Accepted Answer

Vaccination is given at 6 months

Answer

Occurs if the proportion of susceptible children is greater than 20%

Answer

Infects 50% of children in a virgin community

Answer

Occurs every 6-7 years

Question 3

In the Rabies vaccine schedule of 0, 3, 7, 14, 30, 90 days, what does the '0' represent?

Accepted Answer

Day of first injection

Answer

Day of dog bite

Answer

Day of symptom onset

Answer

Day of dog death

Question 4

A baby is brought for immunization for the first time at 18 months of age. Which vaccine(s) can be administered?

Accepted Answer

DPT booster and OPV

Answer

Pentavalent vaccine

Answer

Pentavalent, OPV, DPT, Measles and mumps

Answer

BCG plus OPV

Question 5

Which of the following vaccines can be used in pregnancy in normal circumstances?

Accepted Answer

Influenza trivalent vaccine

Answer

MMR vaccine

Answer

Varicella vaccine

Answer

Hepatitis A vaccine

Question 6

Which of the following Oral Polio Vaccine (OPV) types are currently usable?

Accepted Answer

Only OPV Types 1 and 2

Answer

Only OPV Type 1

Answer

Only OPV Types 1, 2, and 3

Answer

Only OPV Types 3 and 4

Question 7

What is the recommended dose of Rabies immunoglobulin?

Accepted Answer

20 IU/kg body weight

Answer

10 IU/Kg body weight

Answer

15 IU/kg body weight

Answer

25 IU/kg body weight

Question 8

Which of the following is true about the varicella vaccine?

Accepted Answer

Salicylates should be avoided for 4-6 weeks after vaccination.

Answer

It is poorly immunogenic.

Answer

The immunity lasts for 4-6 months.

Answer

It is given to children less than 12 months of age if they do not have chickenpox.

Question 9

Which of the following vaccines has maximum efficacy after a single dose?

Accepted Answer

Measles

Answer

Tetanus toxoid

Answer

DPT

Answer

Typhoid

Question 10

How often are booster doses recommended for the ViPS vaccine?

Accepted Answer

Every 3 years

Answer

Every year

Answer

Every 2 years

Answer

Every 4 years

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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