Immunization and Vaccine-Preventable Diseases — MCQs
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BCG vaccine is diluted with:
A 20-year-old female diagnosed with acute myeloid leukemia underwent allogeneic stem cell transplantation one year ago. During a follow-up visit, she presents with manifestations of chronic graft-versus-host disease but is otherwise doing well and has no evidence of recurrence. Which of the following vaccines should not be administered to this patient at this point in time?
What is the seroconversion rate after completing the 3-dose Hepatitis B vaccine series?
Zero dose of polio vaccine is given at which point?
Which vaccine should not be administered during pregnancy?
Which of the following statements regarding the oral polio vaccine (OPV) is not true?
Rubella vaccination is contraindicated in all except?
Under the national polio eradication program, after how many days is a case of acute flaccid paralysis confirmed as polio by surveillance?
Which of the following is NOT true regarding the surveillance of acute flaccid paralysis in the context of a national polio eradication program?
If a mother is vaccinated for rubella in the preconception period, what is the recommended waiting period before conception to ensure optimal protection against rubella infection in the child?
Immunization and Vaccine-Preventable Diseases Indian Medical PG Practice Questions and MCQs
Question 141: BCG vaccine is diluted with:
- A. Normal saline (Correct Answer)
- B. Distilled water
- C. Dextrose
- D. Colloids
Explanation: **Explanation:** The BCG (Bacillus Calmette-Guérin) vaccine is a live attenuated lyophilized (freeze-dried) vaccine. It must be reconstituted before administration using **Normal Saline (0.9% NaCl)** as the specific diluent. **Why Normal Saline?** Normal saline is isotonic and chemically compatible with the live attenuated *Mycobacterium bovis* strain. It maintains the pH and osmotic balance necessary to preserve the viability of the live bacilli. Using the wrong diluent can lead to vaccine failure or increased adverse reactions. **Why other options are incorrect:** * **Distilled Water:** It is hypotonic. Using distilled water causes the live bacilli to swell and burst due to osmotic pressure, rendering the vaccine ineffective. It is also associated with increased local irritation and pain at the injection site. * **Dextrose:** The sugar content can alter the stability of the vaccine and may promote the growth of contaminants once the vial is opened. * **Colloids:** These are large molecular weight substances used for volume expansion and are never used as vaccine diluents. **High-Yield Clinical Pearls for NEET-PG:** * **Reconstitution Rule:** Once reconstituted, the BCG vaccine must be used within **4–6 hours**. Any leftover vaccine must be discarded to prevent contamination (specifically *Staphylococcal* toxic shock syndrome). * **Storage:** The diluent should be stored at the same temperature as the vaccine (**2°C to 8°C**) before mixing to avoid thermal shock to the organisms. * **Other Diluents:** Remember that **Measles/MR** vaccines use **Distilled Water** as a diluent, unlike BCG. * **Site/Route:** BCG is given **Intradermally** (Left Deltoid) using an **Omega/Tuberculin syringe**.
Question 142: A 20-year-old female diagnosed with acute myeloid leukemia underwent allogeneic stem cell transplantation one year ago. During a follow-up visit, she presents with manifestations of chronic graft-versus-host disease but is otherwise doing well and has no evidence of recurrence. Which of the following vaccines should not be administered to this patient at this point in time?
- A. Diphtheria-tetanus
- B. 23-Valent pneumococcal polysaccharide
- C. Measles, mumps, and rubella (Correct Answer)
- D. Poliomyelitis injection
Explanation: **Explanation** The core concept tested here is the contraindication of **live-attenuated vaccines** in immunocompromised individuals. **1. Why "Measles, mumps, and rubella (MMR)" is the correct answer:** MMR is a live-attenuated vaccine. In patients who have undergone Hematopoietic Stem Cell Transplantation (HSCT), live vaccines are strictly contraindicated for at least **24 months** post-transplant. Furthermore, they should only be administered if the patient is free of **Graft-versus-Host Disease (GvHD)** and has been off all immunosuppressive therapy for at least 3–11 months. This patient has active chronic GvHD, making the administration of a live vaccine highly dangerous due to the risk of unchecked viral replication. **2. Why the other options are incorrect:** * **A & D (Diphtheria-tetanus and IPV):** These are **inactivated/killed vaccines** (or toxoids). Inactivated vaccines do not pose a safety risk of causing disease in immunocompromised hosts. Post-HSCT protocols typically recommend restarting the primary series of these vaccines 6–12 months after transplantation. * **B (23-Valent pneumococcal polysaccharide):** This is a subunit/polysaccharide vaccine. It is not live and is actually a high-priority vaccine for HSCT recipients to prevent invasive pneumococcal disease, usually administered starting 6–12 months post-transplant. **Clinical Pearls for NEET-PG:** * **HSCT Rule:** Inactivated vaccines start at **6 months** post-transplant; Live vaccines start at **24 months** (only if no GvHD). * **GvHD Status:** Active GvHD is a definitive contraindication for live vaccines, regardless of the time elapsed since transplant. * **Household Contacts:** Family members of immunocompromised patients *should* receive MMR and Varicella vaccines (to provide herd immunity), but should avoid the Oral Polio Vaccine (OPV) as the virus can be shed in stools. Always prefer **Inactivated Polio Vaccine (IPV)**.
Question 143: What is the seroconversion rate after completing the 3-dose Hepatitis B vaccine series?
- A. 30%
- B. 50%
- C. 70%
- D. 95% (Correct Answer)
Explanation: ### Explanation **Correct Answer: D (95%)** The Hepatitis B vaccine is a highly immunogenic, recombinant DNA vaccine containing the Hepatitis B surface antigen (HBsAg). The standard 3-dose schedule (administered at 0, 1, and 6 months) is designed to induce a robust immune response. **Seroconversion** is defined as achieving a protective antibody titer (Anti-HBs) of **≥10 mIU/mL**. In healthy infants, children, and adults under the age of 40, the completion of the 3-dose series results in a protective antibody response in **more than 95%** of recipients. **Analysis of Incorrect Options:** * **Options A (30%) and B (50%):** These rates are significantly lower than the established efficacy of the Hep B vaccine. Such low rates might only be seen in severely immunocompromised individuals or those with end-stage renal disease. * **Option C (70%):** While higher, this still underestimates the vaccine's potency. A 70% response rate might be observed after only two doses, but the third dose is crucial for reaching the >95% threshold and ensuring long-term memory. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Injection:** In adults, it must be given in the **deltoid muscle**. Gluteal injection is avoided as it leads to lower seroconversion rates due to deposition in fat. In infants, the **anterolateral aspect of the thigh** is used. * **Non-responders:** Approximately 5–10% of individuals may not respond to the primary series. Risk factors include age (>40 years), obesity, smoking, and chronic diseases. * **Schedule:** Under the National Immunization Schedule (NIS) in India, it is given at 0, 6, 10, and 14 weeks (as part of the Pentavalent vaccine, plus a birth dose). * **Storage:** It is a **heat-stable but freeze-sensitive** vaccine (stored at +2°C to +8°C). It must never be frozen (Shake Test is used to check if it was frozen).
Question 144: Zero dose of polio vaccine is given at which point?
- A. Before giving DPT
- B. At birth (Correct Answer)
- C. When a child is having diarrhea
- D. When a child is having polio
Explanation: **Explanation:** The term **"Zero Dose"** refers to the dose of Oral Polio Vaccine (OPV) administered **at birth** (or as soon as possible within the first 15 days). **Why "At Birth" is Correct:** The primary objective of the zero dose is to ensure early intestinal immunity before the infant is exposed to enteric pathogens. It overcomes the interference of maternal antibodies and induces local mucosal immunity (IgA) in the gut. It is called "Zero" because it does not count toward the primary three-dose schedule (6, 10, and 14 weeks) required for full protection under the National Immunization Schedule (NIS). **Analysis of Incorrect Options:** * **A. Before giving DPT:** While OPV is co-administered with DPT/Pentavalent at 6, 10, and 14 weeks, the specific "Zero Dose" designation is reserved strictly for the birth dose. * **C. When a child is having diarrhea:** Diarrhea is not a contraindication for OPV. In fact, if a child has diarrhea during a scheduled dose, the dose is given but **not counted**; an extra dose must be administered after recovery. This is a "repeat dose," not a "zero dose." * **D. When a child is having polio:** Vaccination is a preventive measure. If a child already has paralytic poliomyelitis, the vaccine will not cure the condition, though they should still complete their immunization to protect against other strains (P1, P3). **High-Yield Clinical Pearls for NEET-PG:** * **Maximum Age:** OPV Zero dose can be given up to **15 days** of age. * **Type of Vaccine:** OPV is a **Live Attenuated** vaccine (Sabin). * **Storage:** OPV is the most **heat-sensitive** vaccine; it is stored at -20°C (deep freezer) and monitored via the **Vaccine Vial Monitor (VVM)** on the label. * **Current Status:** India currently uses **bOPV** (containing types 1 and 3) in routine immunization, supplemented by **fractional IPV (fIPV)** at 6 and 14 weeks.
Question 145: Which vaccine should not be administered during pregnancy?
- A. MMR (Correct Answer)
- B. Rabies
- C. Hepatitis B
- D. Diphtheria
Explanation: ### Explanation **Correct Answer: A. MMR** The fundamental principle in obstetric immunization is that **Live Attenuated Vaccines** are generally **contraindicated** during pregnancy. The MMR (Measles, Mumps, and Rubella) vaccine contains live viruses that theoretically pose a risk of transplacental transmission to the fetus. Specifically, the Rubella component carries a theoretical risk of causing Congenital Rubella Syndrome (CRS), although accidental vaccination has rarely shown clinical harm. Women are advised to avoid pregnancy for at least 4 weeks after receiving the MMR vaccine. **Why the other options are incorrect:** * **B. Rabies:** This is a **killed vaccine**. Since rabies is a 100% fatal disease, post-exposure prophylaxis (PEP) is never withheld in pregnancy. It is safe and mandatory if indicated. * **C. Hepatitis B:** This is a **subunit (recombinant) vaccine**. It is not contraindicated and is administered to pregnant women at high risk of infection. * **D. Diphtheria:** Administered as part of the **Tdap or Td** regimen. In India, under the National Immunization Schedule (NIS), two doses of Tetanus and adult Diphtheria (Td) vaccine are standard care to prevent maternal and neonatal tetanus/diphtheria. **High-Yield NEET-PG Pearls:** 1. **Absolute Contraindications in Pregnancy:** MMR, Varicella, Yellow Fever, Zoster, and Live Attenuated Influenza Vaccine (LAIV). 2. **Exception:** Yellow Fever vaccine may be given if the risk of travel to an endemic zone outweighs the risk of vaccination. 3. **Safe Vaccines:** All killed/inactivated vaccines, toxoids (Tetanus, Diphtheria), and recombinant vaccines (Hep B). 4. **Influenza:** The **Inactivated** Influenza Vaccine is specifically recommended for all pregnant women during flu season as they are at high risk for complications.
Question 146: Which of the following statements regarding the oral polio vaccine (OPV) is not true?
- A. Useful in epidemics
- B. Excretion of the virus in stools can lead to disease in the unimmunized (Correct Answer)
- C. Provides a rapid antibody response
- D. Protective even in the presence of maternal antibodies
Explanation: ### Explanation The correct answer is **B**, as the statement is factually incorrect regarding the standard behavior of OPV. **1. Why Option B is the "Not True" statement:** When a child is vaccinated with OPV (Sabin vaccine), the attenuated virus multiplies in the gut and is excreted in the stools. This excreted virus can spread to unimmunized contacts in the community. However, this process—known as **"Contact Immunity"**—is actually a **beneficial** feature of OPV, as it passively immunizes the community. It does **not** lead to disease in the unimmunized unless the virus undergoes rare genetic mutations over a long period (leading to VDPV), but the general principle of OPV excretion is protective, not pathogenic. **2. Analysis of Incorrect Options:** * **Option A (Useful in epidemics):** True. OPV is the vaccine of choice during outbreaks because it induces rapid local gut immunity (IgA), which breaks the chain of transmission faster than IPV. * **Option C (Rapid antibody response):** True. OPV induces both systemic (IgG) and local mucosal (IgA) immunity quickly, making it highly effective for mass immunization campaigns. * **Option D (Protective in presence of maternal antibodies):** True. Unlike many live vaccines (like Measles), OPV is not significantly neutralized by maternal antibodies, which is why the "Zero Dose" is given at birth. **3. NEET-PG High-Yield Pearls:** * **Vaccine of Choice for Outbreaks:** OPV (due to rapid gut immunity). * **Vaccine of Choice for Immunodeficient children:** IPV (Salk), as OPV can cause Vaccine-Associated Paralytic Polio (VAPP). * **Herd Immunity:** OPV provides excellent herd immunity via contact immunization; IPV provides no herd immunity. * **Current Schedule (India):** bOPV (Type 1 & 3) is used; Type 2 was removed globally in 2016 (The Switch). Fractional dose IPV (fIPV) is now given at 6, 14 weeks, and 9 months.
Question 147: Rubella vaccination is contraindicated in all except?
- A. Patient on immunosuppressants
- B. Girl with leukemia
- C. Girls between 11-14 years (Correct Answer)
- D. Pregnancy
Explanation: ### Explanation The core concept tested here is the nature of the **Rubella vaccine**, which is a **Live Attenuated Vaccine** (RA 27/3 strain). Live vaccines are generally contraindicated in individuals with compromised immune systems or during pregnancy due to the theoretical risk of the vaccine virus causing disease or congenital defects. **Why Option C is Correct:** Girls between **11-14 years** (adolescents) are a primary target group for Rubella vaccination. The goal is to provide immunity before they reach childbearing age to prevent **Congenital Rubella Syndrome (CRS)**. While the vaccine is contraindicated *during* pregnancy, it is highly recommended for non-pregnant adolescent girls and women of reproductive age. **Why the Other Options are Wrong:** * **Option A (Immunosuppressants):** Live vaccines can cause uncontrolled replication of the vaccine virus in patients on high-dose corticosteroids or chemotherapy, leading to severe systemic infection. * **Option B (Leukemia):** Malignancies of the immune system (like leukemia or lymphoma) are absolute contraindications for live vaccines because the host cannot mount an effective response to contain the attenuated virus. * **Option C (Pregnancy):** There is a theoretical risk of the live virus crossing the placenta and causing CRS. Therefore, pregnancy is a contraindication, and pregnancy should be avoided for **1 month** (formerly 3 months) after vaccination. **High-Yield NEET-PG Pearls:** * **Vaccine Strain:** RA 27/3 (grown in human diploid cells). * **Dose/Route:** 0.5 ml, Subcutaneous. * **Storage:** Most sensitive to light (must be protected). * **CRS Prevention:** The primary objective of Rubella vaccination is not just to protect the individual, but to prevent fetal infection in utero. * **Post-Exposure:** Rubella vaccine does not provide post-exposure prophylaxis (unlike Measles).
Question 148: Under the national polio eradication program, after how many days is a case of acute flaccid paralysis confirmed as polio by surveillance?
- A. 15 days
- B. 30 days
- C. 60 days (Correct Answer)
- D. 90 days
Explanation: ### Explanation The correct answer is **60 days**. Under the **Global Polio Eradication Initiative (GPEI)** and India’s National Surveillance program, the confirmation of a case as "Polio" or "Non-Polio AFP" is based on the presence of **residual paralysis**. 1. **Why 60 days is correct:** Acute Flaccid Paralysis (AFP) can be caused by various etiologies (e.g., Guillain-Barré Syndrome, Transverse Myelitis). However, paralysis caused by the Poliovirus is typically permanent. Therefore, the protocol mandates a **60-day follow-up examination**. If the child still exhibits weakness or paralysis after 60 days, the case is clinically compatible with polio (if virological tests were inconclusive) or confirmed as polio (if wild poliovirus was isolated). 2. **Why other options are incorrect:** * **15 days:** This is the window for "adequate stool collection." Two stool samples must be collected 24–48 hours apart within 14 days of the onset of paralysis. * **30 days:** This is too early to determine if paralysis is permanent, as many non-polio AFP cases show significant recovery within a month. * **90 days:** While follow-up can occur later, the standard surveillance milestone for classification is 60 days. ### High-Yield Clinical Pearls for NEET-PG: * **AFP Surveillance Criteria:** Includes any child <15 years with sudden onset of flaccid paralysis or a person of any age where polio is suspected. * **Stool Samples:** Must be sent under "Reverse Cold Chain" (maintained at 2–8°C) to the laboratory. * **Zero Polio Status:** India was declared Polio-free by the WHO on **March 27, 2014**, after three consecutive years of zero indigenous cases (last case: Jan 13, 2011, in Howrah, West Bengal). * **Vaccine Change:** India switched from Trivalent OPV to **Bivalent OPV** (containing types 1 and 3) in April 2016, alongside the introduction of **Inactivated Polio Vaccine (IPV)**.
Question 149: Which of the following is NOT true regarding the surveillance of acute flaccid paralysis in the context of a national polio eradication program?
- A. Acute flaccid paralysis is defined in a child less than 15 years of age.
- B. All cases of acute flaccid paralysis should be reported irrespective of diagnosis within 6 months of onset.
- C. Two stool specimens should be collected within 14 days of paralysis onset, at least 24 hours apart.
- D. A follow-up examination should be conducted 30 days after the onset of paralysis. (Correct Answer)
Explanation: ### Explanation **Why Option D is the Correct Answer (The "False" Statement):** In the Acute Flaccid Paralysis (AFP) surveillance protocol, a follow-up clinical examination must be conducted **60 days** after the onset of paralysis, not 30 days. This follow-up is crucial to assess for **residual paralysis**, which is a hallmark of paralytic poliomyelitis. If the patient has residual weakness, died, or was lost to follow-up at the 60-day mark, the case is further scrutinized by the Expert Review Panel. **Analysis of Incorrect Options (True Statements):** * **Option A:** The standard WHO case definition for AFP surveillance includes any child **less than 15 years of age**. Additionally, any case of paralytic illness in a person of any age is reported if polio is suspected. * **Option B:** To ensure high sensitivity, the system requires reporting of **all cases** of sudden onset flaccid weakness, regardless of the suspected clinical diagnosis (e.g., Guillain-Barré Syndrome, transverse myelitis), provided it is reported within a reasonable timeframe for investigation. * **Option C:** "Adequate stool collection" is a key performance indicator. It requires **two stool specimens** collected **24 hours apart** within **14 days** of the onset of paralysis. This ensures maximum viral shedding detection. **High-Yield Clinical Pearls for NEET-PG:** * **AFP Surveillance Indicators:** 1. **Non-polio AFP rate:** Should be $\geq$ 2 per 100,000 children < 15 years (indicates system sensitivity). 2. **Stool Adequacy:** $\geq$ 80% of AFP cases should have two adequate stool samples. * **Zero Reporting:** Health facilities must submit a report every week even if "zero" cases of AFP were detected. * **Reverse Cold Chain:** Stool samples must be transported at 2-8°C to the laboratory to keep the virus viable for culture.
Question 150: If a mother is vaccinated for rubella in the preconception period, what is the recommended waiting period before conception to ensure optimal protection against rubella infection in the child?
- A. 1 month
- B. 2 months
- C. 6 months (Correct Answer)
- D. 12 months
Explanation: ### Explanation **Correct Answer: C. 6 months** **Concept:** The Rubella vaccine is a **live-attenuated vaccine** (RA 27/3 strain). The primary concern with administering live vaccines near or during pregnancy is the theoretical risk of the vaccine virus crossing the placenta and causing **Congenital Rubella Syndrome (CRS)**. While the CDC and WHO suggest a minimum waiting period of 28 days (1 month), the **National Guidelines in India** and several standard textbooks used for NEET-PG (like Park’s Preventive and Social Medicine) traditionally recommend a safer margin of **6 months** to ensure complete clearance of the virus and robust antibody development before conception. **Analysis of Options:** * **Option A (1 month):** This is the minimum period recommended by international bodies (CDC/WHO). However, for Indian competitive exams, the more conservative 6-month window is the standard "textbook" answer. * **Option B (2 months):** This is an intermediate duration and is not a standard guideline for Rubella. * **Option D (12 months):** This is unnecessarily long. Protective immunity is established much earlier, and delaying pregnancy for a year is clinically unwarranted. **High-Yield Clinical Pearls for NEET-PG:** * **Strain used:** RA 27/3 (Human diploid cell culture). * **Contraindication:** Pregnancy is an absolute contraindication for the MMR/Rubella vaccine. * **Accidental Vaccination:** If a pregnant woman is accidentally vaccinated, it is **not** an indication for Medical Termination of Pregnancy (MTP), as the actual risk of CRS from the vaccine strain is negligible. * **Post-partum Vaccination:** The best time to vaccinate a woman of reproductive age is immediately after delivery (post-partum), as there is no risk of pregnancy in the immediate period. * **Storage:** Must be stored at +2°C to +8°C and protected from light.
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Principles of Immunization
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Types of Vaccines
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Universal Immunization Program
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Cold Chain System
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Vaccine Storage and Handling
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Adverse Events Following Immunization
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National Immunization Schedule
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Polio Eradication
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Measles Elimination
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Tetanus Control
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New and Underutilized Vaccines
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Vaccination Coverage Assessment
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