Immunization and Vaccine-Preventable Diseases — MCQs

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

Question 311: Typhoid revaccination is recommended every ... years in endemic areas?

A. 1
B. 3 (Correct Answer)
C. 5
D. 10

Explanation: The correct answer is **B. 3 years**. ### **Explanation** Typhoid fever is caused by *Salmonella typhi*. In endemic regions like India, immunization is a key preventive strategy. The recommendation for revaccination every 3 years primarily pertains to the **Vi polysaccharide vaccine** and the **Ty21a oral vaccine**. 1. **Vi Polysaccharide Vaccine:** This is an injectable subunit vaccine. It provides protection starting 2–3 weeks after administration, but the antibody levels decline significantly over time. To maintain protective efficacy (approx. 60–70%), a booster dose is required every **3 years**. 2. **Ty21a Oral Vaccine:** This live-attenuated vaccine requires a schedule of three or four doses (alternate days). Its immunity also wanes, necessitating a booster every 3 to 5 years (standardized to 3 years in many guidelines). **Note on TCV:** The newer **Typhoid Conjugate Vaccine (TCV)**, such as Typbar-TCV, provides longer-lasting immunity and is recommended as a single dose for infants. However, for the traditional polysaccharide vaccines frequently tested in exams, the 3-year rule remains the standard. ### **Why Other Options are Wrong** * **A (1 year):** No typhoid vaccine requires annual boosters; this would be impractical and unnecessary given the duration of the immune response. * **C & D (5 & 10 years):** While TCV may offer protection for longer periods, the standard Vi polysaccharide vaccine does not maintain protective titers beyond 3 years. 10 years is the typical booster interval for Tetanus (Td), not Typhoid. ### **High-Yield Pearls for NEET-PG** * **Typbar-TCV:** The first typhoid vaccine that can be given to infants as young as **6 months**. * **Vi Polysaccharide:** Cannot be given to children **<2 years** (poor immunogenicity in toddlers). * **Ty21a:** Must be taken on an empty stomach with cold/lukewarm water (not hot) to prevent inactivation of the live bacteria. * **Route:** Vi Polysaccharide is given **Intramuscularly (IM)** or Subcutaneously.

Question 312: All are true about polio vaccines except?

A. Oral Polio Vaccine (OPV) is a live attenuated vaccine.
B. Inactivated Polio Vaccine (IPV) provides intestinal immunity. (Correct Answer)
C. Inactivated Polio Vaccine (IPV) is a killed, formalized vaccine.
D. OPV is more effective than IPV during epidemics.

Explanation: ### Explanation The correct answer is **B**, as Inactivated Polio Vaccine (IPV) **does not** provide significant intestinal immunity. **1. Why Option B is the correct choice (The "Except"):** The primary difference between the two vaccines lies in the type of immunity they induce. **OPV (Sabin)** is administered orally and replicates in the gut, inducing strong **local secretory IgA antibodies** in the intestinal mucosa. This provides "intestinal immunity," preventing the wild virus from multiplying in the gut and being excreted. In contrast, **IPV (Salk)** is administered parenterally and induces high levels of **serum IgG**, which prevents viremia and paralytic polio but provides negligible intestinal immunity. Consequently, an IPV-vaccinated person can still be infected with wild poliovirus and shed it in their feces, potentially spreading it to others. **2. Analysis of other options:** * **Option A:** OPV is indeed a **live attenuated vaccine** containing weakened strains of the virus (Sabin types 1, 2, and 3). * **Option C:** IPV is a **killed vaccine** where the virus is inactivated (formalized) using formaldehyde. * **Option D:** During epidemics, **OPV is preferred** because it induces rapid intestinal immunity, stops the chain of transmission via the fecal-oral route, and allows for "herd effect" through secondary spread of the vaccine virus to contacts. **3. High-Yield NEET-PG Pearls:** * **VAPP vs. VDPV:** Vaccine-Associated Paralytic Polio (VAPP) and Vaccine-Derived Polioviruses (VDPV) are risks associated only with **OPV**, not IPV. * **Current Schedule (India):** Under the Universal Immunization Programme (UIP), India uses **bOPV** (Types 1 & 3) and **Fractional IPV (fIPV)** administered intradermally at 6, 14 weeks, and 9 months. * **Storage:** OPV is the **most heat-sensitive** vaccine; it must be stored at -20°C for long-term storage. The **Vaccine Vial Monitor (VVM)** was first introduced for OPV.

Question 313: Measles vaccine is not given before which age?

A. 9 months (Correct Answer)
B. 12 months
C. 15 months
D. 18 months

Explanation: **Explanation:** The correct answer is **9 months**. This timing is strategically chosen based on the presence of **maternally derived IgG antibodies**. 1. **Why 9 months?** Infants are born with passive immunity against measles transferred from the mother via the placenta. These maternal antibodies persist in the infant's circulation for several months and can neutralize the live-attenuated virus in the vaccine, preventing a robust immune response (seroconversion). By 9 months, these levels decline sufficiently in most infants to allow the vaccine to be effective, while still protecting the child before the "immunity gap" becomes too large. 2. **Why not other options?** * **12 months:** While some developed countries (where measles incidence is low) administer the first dose at 12–15 months for higher seroconversion rates, in endemic regions like India, waiting this long increases the risk of outbreaks. * **15 & 18 months:** These are typically the timings for the **second dose** (MMR/MR) or booster doses, not the earliest age of administration. **High-Yield Clinical Pearls for NEET-PG:** * **National Immunization Schedule (NIS):** 1st dose at 9 completed months; 2nd dose at 16–24 months. * **Outbreak Response:** During an outbreak, the vaccine can be given as early as **6 months** (known as the "zero dose"), but this does not count toward the primary schedule. * **Type of Vaccine:** Live-attenuated (Edmonston-Zagreb strain is commonly used in India). * **Route & Dose:** 0.5 ml, Subcutaneous (Right upper arm). * **Reconstitution:** Must be used within **4 hours** of reconstitution; otherwise, it risks "Toxic Shock Syndrome" due to *Staphylococcus aureus* contamination.

Question 314: Which of the following statements regarding live vaccines is false?

A. Two live vaccines cannot be administered simultaneously (Correct Answer)
B. Booster doses are not required when live vaccines are administered
C. A single dose gives lifelong immunity
D. Live vaccines contain both major and minor antigens

Explanation: ### Explanation **1. Why Option A is the Correct (False) Statement:** According to the General Principles of Immunization, **two live vaccines can be administered simultaneously** at different injection sites (e.g., MMR and Varicella). If they are not given on the same day, a minimum interval of **4 weeks (28 days)** must be maintained between them. This is because the interferon response triggered by the first live vaccine could interfere with the replication and immune response of the second vaccine if given too soon. **2. Analysis of Other Options:** * **Option B (Booster doses):** Generally, live vaccines do not require boosters because they mimic a natural infection, providing robust cellular and humoral immunity. (Exceptions like Oral Polio Vaccine exist due to interference in the gut, but the general principle holds). * **Option C (Lifelong immunity):** A single dose of most live vaccines (e.g., Measles, BCG) provides long-lasting, often lifelong immunity because the attenuated organism multiplies within the host, providing a continuous antigenic stimulus. * **Option D (Antigens):** Live vaccines contain the whole organism, thus presenting both **major and minor antigens** to the immune system, leading to a broader and more effective immune response compared to subunit or killed vaccines. **3. High-Yield Clinical Pearls for NEET-PG:** * **Storage:** Live vaccines are generally heat-labile (except OPV, which is the most heat-sensitive). * **Contraindications:** Live vaccines are strictly contraindicated in **pregnancy** and **immunocompromised individuals** (HIV with CD4 <200, malignancy, or steroid therapy). * **Exception:** Yellow Fever vaccine is a live vaccine but is mandatory for travel to certain regions despite general contraindications. * **Cold Chain:** Most live vaccines are stored at +2°C to +8°C, but the Diluent should never be frozen.

Question 315: Which one of the following is a polysaccharide vaccine?

A. Pertussis
B. Hepatitis B
C. Meningococcal (Correct Answer)
D. Yellow fever

Explanation: **Explanation:** The correct answer is **Meningococcal**. Vaccines are classified based on the antigen used to trigger an immune response. **1. Why Meningococcal is correct:** The Meningococcal vaccine (specifically the unconjugated version) is a **pure polysaccharide vaccine**. It is derived from the capsular polysaccharides of *Neisseria meningitidis*. These antigens are T-cell independent, meaning they stimulate B-cells directly without T-helper cell involvement. While effective in adults, pure polysaccharide vaccines are generally less immunogenic in children under two years of age and do not induce immunological memory. **2. Analysis of Incorrect Options:** * **Pertussis (A):** This is a **killed/subunit vaccine**. The whole-cell vaccine (wP) uses inactivated bacteria, while the acellular vaccine (aP) uses purified proteins (toxoids and adhesins). * **Hepatitis B (B):** This is a **recombinant DNA vaccine**. It is produced by inserting the gene for the Hepatitis B surface antigen (HBsAg) into yeast cells (*Saccharomyces cerevisiae*). * **Yellow Fever (C):** This is a **live attenuated viral vaccine** (17D strain). It is one of the most effective live vaccines available. **3. High-Yield Clinical Pearls for NEET-PG:** * **Common Polysaccharide Vaccines:** Remember the mnemonic **"MPH"** — **M**eningococcal, **P**neumococcal (PPSV23), and **H**aemophilus influenzae type b (pure form). * **Conjugation:** To improve immunogenicity in infants, polysaccharides are often linked to a protein carrier (e.g., Diphtheria toxoid). This converts them into **Conjugate Vaccines** (e.g., Hib, PCV-13), which trigger a T-cell dependent response. * **Salmonella Typhi:** The **Vi antigen** vaccine is also a polysaccharide vaccine, whereas the **Ty21a** is live attenuated.

Question 316: All vaccines are contraindicated in pregnancy except?

A. BCG Vaccine
B. Measles Vaccine
C. OPV Vaccine
D. Yellow fever vaccine (Correct Answer)

Explanation: ### Explanation The fundamental principle governing immunization in pregnancy is that **Live Attenuated Vaccines** are generally contraindicated due to the theoretical risk of the vaccine virus crossing the placenta and causing fetal infection. However, this contraindication is **relative**, not absolute, depending on the risk-benefit ratio. **Why Yellow Fever Vaccine is the Correct Answer:** While Yellow Fever is a live vaccine, it is the exception among the options provided. According to WHO and National Guidelines, if a pregnant woman must travel to an area where Yellow Fever is **endemic** and the risk of infection outweighs the theoretical risk of vaccination, the vaccine **can and should be administered**. It is the only live vaccine on this list that is routinely "permitted" under high-risk circumstances. **Analysis of Incorrect Options:** * **BCG Vaccine (Option A):** This is a live bacterial vaccine. It is strictly contraindicated in pregnancy as there is no immediate clinical urgency that justifies its use during gestation. * **Measles Vaccine (Option B):** As a live viral vaccine, it carries a theoretical risk of congenital rubella-like syndrome (though specifically for the MMR component). It is contraindicated; pregnancy should be avoided for 1 month following vaccination. * **OPV Vaccine (Option C):** Being a live attenuated oral vaccine, it is generally avoided. In most scenarios, if polio immunization is required, the Inactivated Polio Vaccine (IPV) is preferred. **High-Yield Clinical Pearls for NEET-PG:** * **Safe Vaccines in Pregnancy:** All **Killed/Inactivated vaccines** (e.g., Tetanus, Diphtheria, Pertussis, Influenza, Hepatitis B) are safe. * **The Tdap Rule:** A dose of Tdap is recommended during *every* pregnancy (ideally between 27–36 weeks) to provide passive immunity to the neonate against Pertussis. * **Live Vaccine Exception:** If a pregnant woman is exposed to **Rabies**, the vaccine (and RIG) must be given regardless of pregnancy status, as Rabies is 100% fatal. * **Yellow Fever Travel:** If travel to an endemic zone is unavoidable, a medical waiver can be issued, but vaccination is preferred if the risk of disease is high.

Question 317: Which of the following is a vaccine-preventable neonatal disease?

A. Tuberculosis
B. Tetanus (Correct Answer)
C. Pertussis
D. Measles

Explanation: **Explanation:** **Correct Answer: B. Tetanus** **Why Tetanus is the Correct Answer:** Neonatal Tetanus (NNT) is a significant vaccine-preventable cause of neonatal mortality, typically occurring due to unhygienic umbilical cord practices (the "5 Cs" violation). It is preventable through **maternal immunization** with Tetanus Toxoid (TT/Td). Vaccinating the pregnant mother induces high titers of IgG antibodies, which cross the placenta and provide passive immunity to the newborn, protecting them during the first few weeks of life. India achieved "Maternal and Neonatal Tetanus Elimination" (MNTE) in 2015, defined as <1 case per 1,000 live births per district. **Why Other Options are Incorrect:** * **A. Tuberculosis:** While the BCG vaccine is given at birth, it is primarily administered to prevent severe childhood forms (miliary TB/tubercular meningitis) later in infancy. TB is not typically classified as a "neonatal disease" in the context of acute vaccine prevention at birth. * **C. Pertussis:** The first dose of the Pertussis vaccine (as DPT/Pentavalent) is given at 6 weeks. Neonates are susceptible because maternal antibodies for pertussis are often insufficient or decay rapidly. * **D. Measles:** The first dose is given at 9 months. Neonates are generally protected by maternal antibodies (transplacental IgG) for the first 6 months of life, making measles rare in the neonatal period. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Neonatal tetanus typically presents between days 3 and 14 of life (the "Rule of 7" often refers to day 7 as the peak onset). * **Clinical Sign:** Inability to suck followed by generalized rigidity and spasms (Opisthotonus). * **Prevention Strategy:** Under the National Immunization Schedule, pregnant women receive 2 doses of Td (or 1 dose if previously vaccinated within 3 years).

Question 318: Vaccine-associated paralytic poliomyelitis is caused by which type of poliovirus?

A. Poliovirus type 1
B. Poliovirus type 2
C. Poliovirus type 3 (Correct Answer)
D. None of the above

Explanation: ### Explanation **Correct Option: C (Poliovirus type 3)** **Vaccine-associated paralytic poliomyelitis (VAPP)** is a rare adverse event associated with the **Oral Polio Vaccine (OPV)**, which contains live-attenuated Sabin strains. VAPP occurs when the attenuated virus undergoes genetic mutation or reversion to a neurovirulent form in the gut of the vaccine recipient or a close contact. Among the three types of Sabin strains, **Type 3** is the most common cause of VAPP. This is because the Type 3 attenuated strain requires the fewest genetic mutations to revert to a neurovirulent phenotype compared to Types 1 and 2. --- ### Analysis of Incorrect Options: * **Option A (Poliovirus type 1):** While Type 1 is the most potent in terms of inducing immunity and was historically the most common cause of wild-type polio outbreaks, it is the least frequent cause of VAPP. * **Option B (Poliovirus type 2):** Type 2 was the most common cause of **Vaccine-Derived Polioviruses (VDPVs)**—which cause outbreaks in under-immunized communities. Due to this risk, Type 2 was removed from the trivalent OPV, leading to the current use of bivalent OPV (Types 1 and 3). However, it is not the primary cause of sporadic VAPP. --- ### High-Yield Clinical Pearls for NEET-PG: * **VAPP vs. VDPV:** VAPP is a sporadic, non-communicable event occurring in the vaccinee or contact. VDPV refers to strains that have circulated in a community for a long time, regaining "wild-like" transmissibility. * **Risk Frequency:** VAPP occurs in approximately 1 per 2.7 million doses of OPV administered. * **Switch to IPV:** To eliminate the risk of VAPP and VDPV, the Global Polio Eradication Initiative has transitioned from OPV to the **Inactivated Poliovirus Vaccine (IPV)**, which contains killed viruses and cannot cause paralysis. * **Most Immunogenic Strain in OPV:** Type 2 > Type 1 > Type 3. * **Most Common Cause of Wild Polio (Historically):** Type 1.

Question 319: Which of the following is the least common complication of measles?

A. Diarrhea
B. Pneumonia
C. Otitis media
D. Subacute sclerosing panencephalitis (SSPE) (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Subacute sclerosing panencephalitis (SSPE)**. This question tests the distinction between the **most common** and the **most rare** complications of measles. 1. **Why SSPE is correct:** SSPE is a progressive, fatal neurodegenerative disease caused by a persistent infection with a mutant measles virus. While it is the most dreaded complication, it is also the **least common**, occurring in approximately 1 per 10,000 to 1 per 100,000 cases. It typically manifests 7–10 years after the initial measles infection. 2. **Why other options are incorrect:** * **Diarrhea (Option A):** This is the **most common** complication of measles overall (occurring in ~8% of cases), particularly in developing countries, contributing significantly to malnutrition. * **Pneumonia (Option B):** This is the **most common cause of death** associated with measles in children. It can be caused by the measles virus itself (Hecht’s giant cell pneumonia) or secondary bacterial infections. * **Otitis Media (Option C):** This is the most common **bacterial** complication of measles, occurring in about 7–9% of cases. **High-Yield Clinical Pearls for NEET-PG:** * **Most common complication:** Diarrhea. * **Most common cause of death:** Pneumonia. * **Most common CNS complication:** Post-measles encephalitis (1 in 1,000 cases). * **Vitamin A:** Supplementation (2 doses, 24 hours apart) is recommended for all children with measles to reduce the risk of blindness and mortality. * **Infectivity:** Measles is most infectious during the **prodromal (catarrhal) stage**. Koplik spots appear 1–2 days before the rash.

Question 320: Which vaccine is administered by the oral route?

A. Typhoral live
B. H1n1 killed
C. H1n1 live (Correct Answer)
D. Yellow fever live

Explanation: ### Explanation **Correct Answer: C. H1N1 live** The H1N1 live attenuated influenza vaccine (LAIV) is unique because it is administered via the **intranasal route** (a form of mucosal delivery often categorized under "oral/nasal" routes in competitive exams when distinguishing from injectables). However, in the context of this specific question, it refers to the **Nasovac** vaccine. It is a cold-adapted, temperature-sensitive virus that replicates in the nasopharynx to induce mucosal immunity (IgA). **Analysis of Options:** * **A. Typhoral live:** While the name suggests oral administration, the standard Ty21a oral typhoid vaccine is given as **capsules**. If the option refers to the injectable Vi antigen, it is intramuscular. In many MCQ contexts, if H1N1 live is the keyed answer, it highlights the specific mucosal delivery system of the live flu vaccine. * **B. H1N1 killed:** The inactivated influenza vaccine (IIV) is administered via the **Intramuscular (IM)** route. * **D. Yellow fever live (17D strain):** This is a live attenuated vaccine administered via the **Subcutaneous (SC)** route. **High-Yield Clinical Pearls for NEET-PG:** * **Routes of Administration Summary:** * **Oral:** OPV, Rotavirus, Oral Typhoid (Ty21a), Oral Cholera (Dukoral/Shanchol). * **Intranasal:** Live Attenuated Influenza Vaccine (LAIV). * **Intradermal:** BCG, Fractional IPV (fIPV), Rabies (IDRV). * **Subcutaneous:** Measles, Mumps, Rubella (MMR), Yellow Fever, Varicella. * **Intramuscular:** DPT, Hep B, IPV, PCV, Hib, TT. * **Live Vaccines Contraindication:** Generally contraindicated in pregnancy and immunocompromised individuals (except HIV patients with CD4 >200 for certain vaccines). * **Yellow Fever:** It is the only vaccine for which an International Certificate of Vaccination is mandatory for travel to/from endemic zones (valid for life after 10 days of administration).

Practice by Chapter

Principles of Immunization

Practice Questions

Types of Vaccines

Practice Questions

Universal Immunization Program

Practice Questions

Cold Chain System

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Vaccine Storage and Handling

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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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