Immunization and Vaccine-Preventable Diseases Practice Questions

Q: Typhoid revaccination is recommended every ___ years in an endemic area?

3. **Explanation:** The correct answer is **3 years (Option B)**. This recommendation primarily pertains to the **Ty21a (Oral)** and **Vi Polysaccharide (Injectable)** vaccines, which have been the mainstays of typhoid prevention in endemic regions like India. 1. **Why 3 years is correct:** The immunity provided by the Vi Polysaccharide vaccine and the Ty21a oral vaccine is not lifelong. Clinical studies show that protective antibody levels significantly decline after three years. Therefore, to maintain effective community and individual protection in endemic areas, a booster dose is required every 3 years. 2. **Why other options are incorrect:** * **1 year (A):** While some older whole-cell vaccines had very short durations, modern vaccines provide protection for at least 3 years; annual vaccination is unnecessary and not cost-effective. * **5 & 10 years (C & D):** By 5 to 10 years, the efficacy of polysaccharide and oral vaccines drops to negligible levels, leaving the individual susceptible to *Salmonella typhi*. **NEET-PG High-Yield Pearls:** * **Vi Polysaccharide Vaccine:** Given as a single IM/SC dose. Minimum age: 2 years. * **Ty21a (Oral) Vaccine:** Live attenuated vaccine. Schedule: 1 capsule on days 1, 3, and 5. Minimum age: 6 years. * **Typhoid Conjugate Vaccine (TCV):** This is the "new gold standard." Unlike the others, it is immunogenic in children **>6 months** of age and provides **longer-lasting immunity** (potentially up to 5 years or more), though the 3-year rule remains a common exam benchmark for traditional vaccines. * **Note:** Typhoid vaccines do not provide significant protection against Paratyphoid fever.

Q: What is the seroconversion rate after completing the 3-dose Hepatitis B vaccine series?

95%. ### 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).

Q: What is true regarding tetanus toxoid?

Absorbed toxoid is more beneficial.. ### Explanation **Correct Answer: B. Adsorbed toxoid is more beneficial.** **Why it is correct:** Tetanus toxoid is available in two forms: **Plain** (fluid) and **Adsorbed** (precipitated with aluminum salts). Adsorbed toxoid is superior because the aluminum adjuvant creates a "depot effect" at the injection site. This slows the release of the antigen, providing a more prolonged antigenic stimulus, which results in higher antibody titers and a longer duration of immunity compared to the plain vaccine. **Analysis of Incorrect Options:** * **Option A:** Plain toxoid is rapidly absorbed and eliminated, leading to a shorter duration of protection. It is rarely used today except in specific emergency situations where rapid (but transient) sensitization is needed. * **Option C & D:** These options relate to cold chain maintenance. Tetanus toxoid is **heat-stable but freeze-sensitive**. It should be stored at **+2°C to +8°C**. Freezing (0°C or below) destroys the potency of the vaccine by causing the adjuvant to aggregate. Therefore, while it *should* not be frozen, Option B is the more definitive statement regarding the biological efficacy of the toxoid types. **High-Yield NEET-PG Pearls:** * **Shake Test:** Used to determine if a freeze-sensitive vaccine (like TT, DPT, or HepB) has been damaged by freezing. If the vaccine is "frozen," the sediment settles rapidly after shaking. * **Immunization in Pregnancy:** To prevent neonatal tetanus, two doses of Tetanus-diphtheria (Td) are given to pregnant women (4 weeks apart), or one dose if they were immunized in the last 3 years. * **Type of Immunity:** Tetanus toxoid provides **Active Artificial Immunity**. * **Site of Injection:** Intramuscular (IM) in the deltoid muscle. Subcutaneous injection increases the risk of local reactions.

Q: Zero dose of polio vaccine is given at which point?

At birth. **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.

Q: Which vaccine should not be administered during pregnancy?

MMR. ### 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.

Q: Post-exposure vaccination is indicated for which of the following conditions?

Rabies. **Explanation:** The correct answer is **Rabies**. Post-exposure prophylaxis (PEP) is effective when the incubation period of a disease is long enough to allow the vaccine-induced immune response to develop before the pathogen reaches its target organ. **1. Why Rabies is Correct:** Rabies has a variable and often long incubation period (typically 1–3 months). Because the virus travels via retrograde axonal transport to the CNS, there is a "window of opportunity" to administer the vaccine after exposure. The vaccine induces active immunity (neutralizing antibodies) that intercepts the virus before it reaches the central nervous system. In most clinical scenarios, Rabies PEP also includes Rabies Immunoglobulin (RIG) for immediate passive protection. **2. Why Incorrect Options are Wrong:** * **Typhoid:** This is a bacterial infection (Salmonella Typhi) with a relatively short incubation period (7–14 days). Vaccination is used for pre-exposure prophylaxis (travelers or endemic areas) but is ineffective after exposure. * **Mumps:** Mumps is a viral infection where the vaccine is part of the routine MMR schedule. While some live vaccines (like Measles) can be used post-exposure if given within 72 hours, Mumps vaccination does not provide documented protection once exposure has occurred. **3. NEET-PG High-Yield Pearls:** * **Other Post-Exposure Vaccines:** Apart from Rabies, post-exposure vaccination is indicated for **Hepatitis B, Varicella, and Measles**. * **Tetanus:** Often confused with PEP; however, if a wound is prone to tetanus, we administer a booster or TIG based on immunization history. * **Rabies Schedule (Post-exposure):** For non-immunized individuals, the intramuscular (Essen) schedule is **0, 3, 7, 14, and 28 days**. * **Site of Injection:** Rabies vaccine should be given in the **deltoid muscle** (adults) or anterolateral thigh (children). It should **never** be given in the gluteal region as fat reduces vaccine efficacy.

Q: Which of the following is NOT an indicator for the elimination of neonatal tetanus?

Coverage of three antenatal visits is more than 90%. **Explanation:** The elimination of Neonatal Tetanus (NT) is defined by the World Health Organization (WHO) as reaching a level where the disease is no longer a major public health problem. India officially achieved "Maternal and Neonatal Tetanus Elimination" (MNTE) in 2015. **Why Option C is the correct answer:** While Antenatal Care (ANC) is vital for maternal health, **"three antenatal visits" is not a specific indicator** for NT elimination. The WHO criteria focus on specific interventions that directly prevent Clostridium tetani infection (immunization and clean delivery practices) rather than general ANC frequency. **Analysis of other options (Indicators for NT Elimination):** * **Option A:** The primary epidemiological goal for elimination is an incidence of ** 70% (often targeted at >75% in specific programs)** of deliveries must be conducted by Skilled Birth Attendants (SBA) or in institutional settings. * **Option C:** High immunization coverage is the backbone of prevention. The target is **> 90% coverage of at least two doses of Tetanus Toxoid (TT2/Td2)** or a booster dose among pregnant women. **High-Yield NEET-PG Pearls:** * **MNTE Strategy:** Uses the **"3 Clean"** approach (Clean hands, Clean surface, Clean cord care) and the **"5 Clean"** approach (adding Clean blade and Clean tie). * **Validation:** Elimination is validated at the **District level**, not just the National level. * **Current Protocol:** Under the National Immunization Schedule, TT has been replaced by the **Td (Tetanus and adult Diphtheria)** vaccine. * **Incubation Period:** Commonly follows the **"Rule of 7"** (symptoms typically appear 7 days after birth).

Q: Which of the following statements regarding the oral polio vaccine (OPV) is not true?

Excretion of the virus in stools can lead to disease in the unimmunized. ### 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.

Q: Rubella vaccination is contraindicated in all except?

Girls between 11-14 years. ### 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).

Q: Under the national polio eradication program, after how many days is a case of acute flaccid paralysis confirmed as polio by surveillance?

60 days. ### 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 1

Typhoid revaccination is recommended every ___ years in an endemic area?

Accepted Answer

3

Answer

1

Answer

5

Answer

10

Question 2

What is the seroconversion rate after completing the 3-dose Hepatitis B vaccine series?

Accepted Answer

95%

Answer

30%

Answer

50%

Answer

70%

Question 3

What is true regarding tetanus toxoid?

Accepted Answer

Absorbed toxoid is more beneficial.

Answer

Plain toxoid has a long duration of action.

Answer

Tetanus toxoid should never be frozen.

Answer

Tetanus toxoid should be stored at 0 degrees Celsius.

Question 4

Zero dose of polio vaccine is given at which point?

Accepted Answer

At birth

Answer

Before giving DPT

Answer

When a child is having diarrhea

Answer

When a child is having polio

Question 5

Which vaccine should not be administered during pregnancy?

Accepted Answer

MMR

Answer

Rabies

Answer

Hepatitis B

Answer

Diphtheria

Question 6

Post-exposure vaccination is indicated for which of the following conditions?

Accepted Answer

Rabies

Answer

Typhoid

Answer

Mumps

Answer

None of the above

Question 7

Which of the following is NOT an indicator for the elimination of neonatal tetanus?

Accepted Answer

Coverage of three antenatal visits is more than 90%

Answer

Incidence rate of neonatal tetanus < 0.1 per 1000 live births

Answer

More than 75% of deliveries conducted by trained birth attendants

Answer

Tetanus toxoid (TT2) injection coverage in pregnant mothers is more than 90%

Question 8

Which of the following statements regarding the oral polio vaccine (OPV) is not true?

Accepted Answer

Excretion of the virus in stools can lead to disease in the unimmunized

Answer

Useful in epidemics

Answer

Provides a rapid antibody response

Answer

Protective even in the presence of maternal antibodies

Question 9

Rubella vaccination is contraindicated in all except?

Accepted Answer

Girls between 11-14 years

Answer

Patient on immunosuppressants

Answer

Girl with leukemia

Answer

Pregnancy

Question 10

Under the national polio eradication program, after how many days is a case of acute flaccid paralysis confirmed as polio by surveillance?

Accepted Answer

60 days

Answer

15 days

Answer

30 days

Answer

90 days

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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