Vaccine Immunology and Types (Toxoid, Conjugate, Subunit, mRNA, Cold Chain) MCQs

Microbiology · 31 free questions with answers & explanations.

1. mRNA vaccines (BNT162b2 / mRNA-1273) for SARS-CoV-2 utilize lipid nanoparticles (LNPs) for delivery. The mRNA encodes the spike protein. An essential modification in these mRNA vaccines that increases stability and reduces innate immune activation is:
2. Conjugate vaccines (e.g., Hib vaccine, PCV13, MCV4) link polysaccharide antigens to carrier proteins. The immunological advantage of conjugation over plain polysaccharide vaccines is:
3. A 2-year-old child develops invasive Hib meningitis despite two prior 'Hib' doses given at 6 and 10 weeks. Investigation reveals the vaccine was stored at -5°C (below 0°C freeze) before administration. The most likely cause of vaccine failure is:
4. mRNA COVID-19 vaccines (BNT162b2, mRNA-1273) differ from conventional protein subunit vaccines in a key immunological advantage. This is:
5. Pneumococcal polysaccharide vaccine (PPSV23) is immunologically inferior to PCV13 (13-valent conjugate vaccine) in children under 2 years. The reason is:
6. Hib (Haemophilus influenzae type b) conjugate vaccine uses polyribosylribitol phosphate (PRP) polysaccharide conjugated to a carrier protein. Why is conjugation to a carrier protein essential for efficacy in infants?
7. OPV (oral polio vaccine) is stored at −20°C in the cold chain. A technician discovers the vaccine vial temperature indicator (VVM) has turned dark (inner square darker than outer circle). What action should be taken?
8. The Hib (Haemophilus influenzae type b) conjugate vaccine generates a T-cell dependent immune response. In contrast, the unconjugated Hib polysaccharide vaccine (HbPS) fails to protect infants <2 years. What is the immunological principle that explains why conjugation to a carrier protein (e.g., tetanus toxoid) overcomes this limitation?
9. During cold chain monitoring, a vaccine vial monitor (VVM) on a polio OPV vial shows the inner square darker than the outer circle. A healthcare worker is about to use this vial. What is the correct action?
10. The cold chain requirement for oral polio vaccine (OPV) is more stringent than for inactivated polio vaccine (IPV). OPV is stored at −15°C to −25°C in the cold chain. The key reason is:
11. Conjugate vaccines (e.g., Hib, pneumococcal PCV13, meningococcal MCV4) are superior to polysaccharide vaccines in infants under 2 years because:
12. The Hib (Haemophilus influenzae type b) conjugate vaccine elicits T-cell-dependent immunity in infants under 2 years, unlike the plain polysaccharide vaccine. This is achieved by:
13. The cold chain storage temperature requirement for OPV (oral poliovirus vaccine) in India under the UIP cold chain system is:
14. The PCV13 (13-valent pneumococcal conjugate vaccine) uses carrier protein CRM197 conjugated to capsular polysaccharides. Compared to the 23-valent polysaccharide vaccine (PPSV23), what is the key immunological advantage of the conjugate vaccine in infants?
15. In the cold chain, the vaccine vial monitor (VVM) on an OPV vial changes colour from a white inner square lighter than the outer circle to a dark inner square matching or darker than the outer circle. What does this indicate?
16. The BCG vaccine is a live attenuated vaccine derived from Mycobacterium bovis. In a child with DiGeorge syndrome (thymic aplasia), administering BCG carries a specific risk. What is this risk?
17. A 2-year-old child receives her first dose of Hib conjugate vaccine (PRP-T). Which immunological mechanism explains why conjugate vaccines produce T-cell-dependent immunity, unlike plain polysaccharide vaccines, in children <2 years?
18. The oral polio vaccine (bOPV — bivalent types 1 and 3) is stored at −15 to −25°C in the cold chain. During a health camp, power failure occurs for 20 hours; the vaccine container has a vial monitor (VVM) that shows the inner square darker than the outer circle. What action should be taken?
19. A conjugate vaccine against Haemophilus influenzae type b (Hib) links polysaccharide antigen to a carrier protein. The immunological rationale for conjugation is to:
20. Which of the following correctly describes the mechanism of action of mRNA-based COVID-19 vaccines?
21. Oral poliovirus vaccine (OPV) is stored at what temperature in the primary cold chain, and what is the 'shake test' used to assess?
22. The recombinant hepatitis B vaccine (Engerix-B) is an example of which vaccine type, and why does it not cause hepatitis B infection?
23. A new meningococcal vaccine is described as a 'glycoconjugate vaccine' where the polysaccharide is covalently linked to a carrier protein. What is the primary immunological advantage of conjugation compared to plain polysaccharide vaccines?
24. An mRNA-based COVID-19 vaccine (BNT162b2) uses modified uridine in place of uridine in the mRNA sequence. What is the primary reason for this modification?
25. The cold chain requires that oral polio vaccine (OPV) be stored at which temperature, and what is the vaccine vial monitor (VVM) used for?
26. A child receives the primary series of diphtheria-tetanus-pertussis (DTP) vaccine. The protective antigen in diphtheria component is the toxoid. Which cellular mechanism is MOST responsible for long-term immunological protection after toxoid vaccination?
27. Haemophilus influenzae type b (Hib) conjugate vaccine generates T-cell-dependent immunity compared to plain polysaccharide vaccine. The key modification enabling this is:
28. mRNA vaccines for COVID-19 (BNT162b2, mRNA-1273) are formulated with lipid nanoparticles (LNPs). The primary role of LNPs is:
29. During cold chain monitoring, a freeze indicator in a vaccine box has been triggered. The concerned vaccine that is MOST damaged by freezing is:
30. A traveller receives a meningococcal ACWY conjugate vaccine. Two years later, serum bactericidal antibody (SBA) titres are checked and found to be ≥1:128. What does this SBA titre indicate?
31. The outer membrane vesicle (OMV) component of the 4CMenB (Bexsero) meningococcal B vaccine provides protection primarily against which strain?