Immunization and Vaccine-Preventable Diseases Practice Questions

Q: Which is the strain of the Japanese encephalitis vaccine?

Nakayama strain. **Explanation:** The correct answer is **C. Nakayama strain**. Japanese Encephalitis (JE) vaccines are categorized into inactivated and live-attenuated types. The **Nakayama strain** (and the Beijing-1 strain) are the classic strains used in the production of the mouse-brain-derived inactivated JE vaccine. While many countries have transitioned to the **SA-14-14-2 strain** (a live-attenuated vaccine derived from primary hamster kidney cells), the Nakayama strain remains the historical and frequently tested prototype for inactivated JE vaccines. **Analysis of Incorrect Options:** * **A. Jeryl Lynn strain:** This is the live-attenuated strain used in the **Mumps** vaccine (part of the MMR/MMRV vaccine). * **B. Oka strain:** This is the live-attenuated strain used in the **Varicella** (Chickenpox) and Herpes Zoster vaccines. * **C. 17D strain:** This is the live-attenuated strain used for the **Yellow Fever** vaccine, known for providing long-lasting immunity (up to 10 years or life). **High-Yield Clinical Pearls for NEET-PG:** * **SA-14-14-2:** This is currently the most widely used strain in India’s Universal Immunization Programme (UIP) for the live-attenuated JE vaccine. * **JE Vaccination Schedule (UIP):** Two doses are given—the 1st dose at 9 months (with Measles/MR) and the 2nd dose at 16–24 months (with the DPT booster). * **Vector:** JE is transmitted by the **Culex tritaeniorhynchus** mosquito, which breeds in stagnant water (paddy fields). * **Amplifier Host:** The **Pig** acts as the primary amplifier host for the virus.

Q: How many doses of the MMR vaccine are typically recommended in childhood immunization schedules?

One dose. **Explanation:** The correct answer is **One dose (Option A)**, specifically within the context of the **National Immunization Schedule (NIS)** in India, which is the primary reference for NEET-PG. **1. Why Option A is Correct:** Under the current Universal Immunization Programme (UIP) in India, the **Measles-Rubella (MR)** vaccine has replaced the standalone Measles vaccine. However, where the **MMR** (Measles, Mumps, Rubella) vaccine is specifically utilized in public health programs, it is traditionally administered as a **single dose at 9 completed months** (range 9-12 months). In the NIS, the second dose provided at 16-24 months is typically the MR vaccine. The question specifically asks for the "typical" recommendation in standard childhood schedules; in the Indian context, the primary protection against Mumps is often covered by a single dose if MMR is used. **2. Why Other Options are Incorrect:** * **Option B (Two doses):** While the IAP (Indian Academy of Pediatrics) recommends two doses of MMR (at 9 months and 15 months), the NEET-PG follows the **UIP/WHO guidelines** unless specified otherwise. In the UIP, the second dose is MR, not MMR. * **Options C & D:** Three or four doses are not standard for the MMR vaccine in any primary childhood schedule. Booster requirements beyond the second dose are not routinely indicated for healthy children. **3. High-Yield Clinical Pearls for NEET-PG:** * **Type of Vaccine:** MMR is a **Live Attenuated** vaccine. * **Route & Site:** Subcutaneous (SC) injection, usually in the right upper arm. * **Diluent:** Sterile water (must be used within 4 hours of reconstitution). * **Contraindications:** Pregnancy, severely immunocompromised states (e.g., advanced HIV/AIDS), and history of anaphylaxis to neomycin. * **Mumps Component:** The most common strain used is the **Jerryl Lynn strain**. * **Rubella Component:** The **RA 27/3 strain** is used, grown on human diploid cells.

Q: What is the efficacy of the Measles vaccine after the second dose?

99%. ### Explanation The efficacy of the Measles vaccine is highly dependent on the number of doses administered and the age at which they are given. **1. Why 99% is the Correct Answer:** The Measles vaccine (Live Attenuated, Edmonston-Zagreb strain) is highly immunogenic. While a single dose administered at 9 months provides approximately **95%** protection, a small percentage of children fail to seroconvert (primary vaccine failure). The **second dose** is administered to catch those who did not respond to the first dose. After the completion of a two-dose schedule, the cumulative efficacy reaches **99%**, providing near-total protection against the virus. **2. Analysis of Incorrect Options:** * **90% (Option A):** This is lower than the standard efficacy of even a single dose. * **95% (Option B):** This is the efficacy typically associated with a **single dose** of the measles vaccine when given after 9 months of age. * **100% (Option D):** No vaccine is 100% effective due to biological variations in host immune responses and potential cold chain failures. **3. High-Yield Clinical Pearls for NEET-PG:** * **Schedule:** Under the National Immunization Schedule (NIS) in India, Measles (as MR vaccine) is given in 2 doses: 1st dose at **9-12 months** and 2nd dose at **16-24 months**. * **Type of Vaccine:** Live attenuated vaccine. * **Reconstitution:** Must be reconstituted with **Sterile Water** (Diluent). Once reconstituted, it must be used within **4 hours**; otherwise, it must be discarded due to the risk of *Staphylococcus aureus* contamination (Toxic Shock Syndrome). * **Cold Chain:** It is highly heat-sensitive and must be stored at **+2°C to +8°C** (though it can be frozen at the regional level). * **Contraindication:** Severe immunocompromised states and pregnancy. History of anaphylaxis to neomycin or gelatin.

Q: Which of the following statements about measles is true?

Otitis media is the most common complication.. ### Explanation **Correct Option: B. Otitis media is the most common complication.** In children, **Otitis media** is the most frequent complication associated with measles. While pneumonia is the most common cause of measles-related *death* (especially in developing countries), middle ear infection remains the most common overall morbidity. **Analysis of Incorrect Options:** * **A. The incubation period is 5 days:** This is incorrect. The incubation period for measles is typically **10–14 days** (10 days to the onset of fever and 14 days to the appearance of the rash). * **C. It is caused by an orthomyxovirus:** This is incorrect. Measles is caused by an RNA virus belonging to the **Paramyxoviridae** family (Genus: *Morbillivirus*). Orthomyxoviruses cause Influenza. * **D. A large number of carriers exist:** This is incorrect. Measles is characterized by the **absence of a carrier state**. It is an obligatory human disease with no animal reservoir, which makes it a candidate for potential eradication. **NEET-PG High-Yield Pearls:** * **Koplik’s Spots:** Pathognomonic sign; small bluish-white spots on an erythematous base found on the buccal mucosa opposite the lower 2nd molars during the pre-eruptive stage. * **SSPE (Subacute Sclerosing Panencephalitis):** The most serious, late-onset neurological complication (occurring years after infection). * **Infectivity:** Highly contagious from **4 days before to 5 days after** the appearance of the rash. * **Vitamin A:** Supplementation is recommended for all children with acute measles to reduce the risk of blindness and mortality.

Q: All of the following are used for the transportation of vaccines except?

ILR. **Explanation:** The core concept tested here is the distinction between **storage equipment** and **transportation equipment** within the Cold Chain system. **Why ILR (Ice-Lined Refrigerator) is the correct answer:** An ILR is a **storage device**, not a transportation device. It is the "backbone" of the cold chain at the District and PHC levels. It is designed to maintain a temperature of +2°C to +8°C even during power outages (for up to 20+ hours) due to the tubes of water/ice lining its walls. Because of its size, weight, and requirement for a continuous power source, it is never used for the physical movement of vaccines between locations. **Analysis of Incorrect Options (Transportation Tools):** * **Vaccine Van:** These are specially refrigerated vehicles used for the bulk transport of vaccines from the State or Regional stores to District stores. * **Cold Box:** These are large, insulated containers used for transporting large quantities of vaccines (e.g., from District to PHC) or for emergency storage during power failures. They can maintain the cold chain for several days. * **Vaccine Carriers:** These are smaller insulated containers used to carry small quantities of vaccines (16-20 vials) from the PHC to the sub-centers or outreach session sites (the "last mile" of delivery). **High-Yield Clinical Pearls for NEET-PG:** * **Most Heat Sensitive Vaccine:** Oral Polio Vaccine (OPV). * **Most Heat Resistant Vaccine:** Tetanus Toxoid (TT) / Td. * **Most Cold/Freeze Sensitive Vaccine:** Hepatitis B (followed by DPT/Pentavalent). These must **never** be stored in the freezer or in direct contact with ice packs. * **The "Shake Test":** Used to determine if a freeze-sensitive vaccine (like DPT or Hep B) has been damaged by sub-zero temperatures. * **Placement in ILR:** OPV and Measles are kept at the bottom (coldest part), while Td and Hepatitis B are kept at the top to prevent freezing.

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 the minimum vaccine coverage required in successive birth cohorts for the elimination of measles?

>95%. **Explanation:** The correct answer is **D (>95%)**. **1. Why >95% is correct:** Measles is one of the most highly infectious human diseases, with a Basic Reproduction Number ($R_0$) typically ranging between **12 and 18**. This means a single infected individual can spread the virus to 12–18 susceptible people. To achieve **Elimination** (interruption of indigenous transmission in a geographical area), the level of **Herd Immunity** must be high enough to break the chain of transmission. Using the formula for Herd Immunity Threshold ($HIT = 1 - 1/R_0$), measles requires a population immunity of approximately 92–94%. To account for vaccine efficacy (which is not 100%), the WHO recommends a sustained coverage of **$\geq$95%** with two doses of measles-containing vaccine (MCV) in every district and every birth cohort. **2. Why other options are incorrect:** * **A and B (>70% to >80%):** These levels are insufficient for measles. While 80% coverage might reduce mortality, it allows for periodic outbreaks because the "critical wall" of protected individuals is too low to stop the virus from circulating. * **C (>90%):** While 90% is a target for many other vaccines (like Polio or DPT), it is still below the threshold required to eliminate measles due to its extreme transmissibility. **3. High-Yield Facts for NEET-PG:** * **Elimination vs. Eradication:** Measles is targeted for *elimination* in India (Regional target: 2023, now updated). *Eradication* refers to global extinction (only Smallpox has been eradicated). * **Vaccine Schedule (India):** 1st dose at 9–12 months; 2nd dose at 16–24 months (as MR vaccine). * **MCV1 vs. MCV2:** One dose provides ~85% protection; two doses provide ~97% protection. * **Vitamin A:** Administered along with Measles vaccine to reduce complications and severity.

Question 1

Which is the strain of the Japanese encephalitis vaccine?

Accepted Answer

Nakayama strain

Answer

Jeryl Lynn strain

Answer

Oka strain

Answer

17D vaccine

Question 2

How many doses of the MMR vaccine are typically recommended in childhood immunization schedules?

Accepted Answer

One dose

Answer

Two doses

Answer

Three doses

Answer

Four doses

Question 3

What is the efficacy of the Measles vaccine after the second dose?

Accepted Answer

99%

Answer

90%

Answer

95%

Answer

100%

Question 4

Which of the following statements about measles is true?

Accepted Answer

Otitis media is the most common complication.

Answer

The incubation period is 5 days.

Answer

It is caused by an orthomyxovirus.

Answer

A large number of carriers exist.

Question 5

All of the following are used for the transportation of vaccines except?

Accepted Answer

ILR

Answer

Vaccine van

Answer

Cold box

Answer

Vaccine carriers

Question 6

Which vaccine can be stored at -10°C temperature?

Accepted Answer

Measles

Answer

Polio

Answer

BCG

Answer

DPT

Question 7

An 11-month-old child has received two doses of DTP and polio vaccine. The child presents for further immunization 5 months after the last dose. What is the recommended course of action?

Accepted Answer

Repeat the whole course

Answer

Repeat the second dose and continue the rest of the course

Answer

Give the third dose and continue the course

Answer

Give only the booster dose

Question 8

Pulse Polio Immunization is administration of Oral Polio Vaccine (OPV) to:

Accepted Answer

All children between 0-5 years of age on a single day, irrespective of their previous immunization status

Answer

Children in the age group of 0-1 year only who have not been immunized earlier

Answer

Children in the age group of 12-24 months only, as the booster dose

Answer

All children between 0-5 years of age, whenever there is an outbreak of poliomyelitis

Question 9

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 10

What is the minimum vaccine coverage required in successive birth cohorts for the elimination of measles?

Accepted Answer

>95%

Answer

>70%

Answer

>80%

Answer

>90%

Immunization and Vaccine-Preventable Diseases — MCQs

Immunization and Vaccine-Preventable Diseases — MCQs

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