Vaccine failure and adverse events following immunization (AEFI) MCQs With Answer

Vaccine failure and adverse events following immunization (AEFI) are critical topics for B. Pharm students involved in immunization safety and pharmacovigilance. This introduction highlights causes of primary and secondary vaccine failure, host and vaccine-related factors, cold chain and storage errors, antigenic drift, and immunization error–related reactions. It also explains AEFI classification, causality assessment, surveillance systems, management of serious events such as anaphylaxis, and risk-minimization strategies including proper handling, documentation, and reporting. Understanding these concepts strengthens clinical judgment, regulatory awareness, and safe vaccine practice. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the best definition of primary vaccine failure?

• Loss of protection many years after vaccination due to waning immunity
• Failure to mount an adequate immune response after complete vaccination
• Adverse event caused directly by vaccine constituents
• Incorrect vaccine administration resulting in local reaction

Correct Answer: Failure to mount an adequate immune response after complete vaccination

Q2. Secondary vaccine failure is best described as:

• Immediate allergic reaction after the first dose
• Failure to seroconvert after initial vaccination
• Loss of protective immunity over time despite initial adequate response
• Adverse event due to vaccine contamination

Correct Answer: Loss of protective immunity over time despite initial adequate response

Q3. Which vaccine-related factor most commonly contributes to vaccine failure in immunization programs?

• Antigenic drift of the pathogen
• Cold chain breaches and improper storage/handling
• Patient noncompliance with oral medications
• Simultaneous administration of two different vaccines

Correct Answer: Cold chain breaches and improper storage/handling

Q4. According to WHO, AEFI is defined as:

• Any confirmed allergic reaction caused by vaccine components
• Any untoward medical occurrence following immunization, not necessarily causal
• Only serious reactions that require hospitalization after vaccination
• Only events proven to be caused by immunization

Correct Answer: Any untoward medical occurrence following immunization, not necessarily causal

Q5. Which of the following constitutes a “serious” AEFI?

• Mild local pain lasting 24 hours
• Low grade fever < 38.5°C
• Hospitalization, life-threatening event, or death
• Transient injection site redness without functional impairment

Correct Answer: Hospitalization, life-threatening event, or death

Q6. The most common non-serious AEFIs reported after many vaccines are:

• Guillain–Barré syndrome and encephalopathy
• Injection site reactions and transient fever
• Permanent neurologic deficits
• Severe anaphylaxis requiring ICU care

Correct Answer: Injection site reactions and transient fever

Q7. Which historical example best illustrates vaccine-associated enhanced disease?

• Intussusception after rotavirus vaccine introduction in all settings
• Severe respiratory disease after formalin-inactivated RSV vaccine
• Anaphylaxis after penicillin co-administration with vaccine
• Autoimmune hepatitis following hepatitis B immunization

Correct Answer: Severe respiratory disease after formalin-inactivated RSV vaccine

Q8. What is the recommended minimum observation time after routine vaccination to monitor for immediate severe reactions in most settings?

• No observation required; patient can leave immediately
• 5 minutes
• 30 minutes
• 48 hours of hospital observation

Correct Answer: 30 minutes

Q9. First-line emergency treatment for anaphylaxis following immunization is:

• Intramuscular epinephrine
• Oral antihistamine only
• Intravenous antibiotics
• Subcutaneous insulin

Correct Answer: Intramuscular epinephrine

Q10. The recommended storage temperature for most routine vaccines in the cold chain is:

• Below −20°C
• 2–8°C
• Room temperature (20–25°C)
• Above 30°C to preserve potency

Correct Answer: 2–8°C

Q11. Which vaccine has been associated with a small increased risk of intussusception in some post-marketing studies?

• Inactivated polio vaccine (IPV)
• Rotavirus vaccine
• BCG vaccine
• Oral cholera vaccine

Correct Answer: Rotavirus vaccine

Q12. Common categories used in causality assessment of AEFI include:

• Immediate, delayed, chronic, and acute
• Certain, probable/likely, possible, unlikely, and unclassifiable
• Mild, moderate, severe, and fatal only
• Local, systemic, neuro, and allergic

Correct Answer: Certain, probable/likely, possible, unlikely, and unclassifiable

Q13. Which passive vaccine safety surveillance system is used in the United States?

• Vaccine Adverse Event Reporting System (VAERS)
• European Pharmacovigilance Database (EUDRA)
• WHO Vaccine Safety Net
• National Adverse Event Registry of India (NAERI)

Correct Answer: Vaccine Adverse Event Reporting System (VAERS)

Q14. The difference between active and passive surveillance for AEFI is that passive surveillance:

• Proactively seeks cases through data collection
• Relies on spontaneous reporting by healthcare providers and patients
• Is always more sensitive than active surveillance
• Requires clinical trials rather than routine monitoring

Correct Answer: Relies on spontaneous reporting by healthcare providers and patients

Q15. A definite contraindication to administering live attenuated vaccines is:

• Mild upper respiratory infection without fever
• Current use of high-dose systemic corticosteroids or severe immunosuppression
• History of controlled allergy to unrelated food
• Age over 65 years

Correct Answer: Current use of high-dose systemic corticosteroids or severe immunosuppression

Q16. Maternal antibodies interfering with infant vaccine response is most relevant for which vaccine given very early?

• Measles vaccine given before 9 months
• Influenza vaccine in elderly
• Tdap booster at adolescence
• HPV vaccine in adults

Correct Answer: Measles vaccine given before 9 months

Q17. Lot-to-lot variation causing vaccine failure is primarily due to problems in:

• Cold chain monitoring at the clinic only
• Manufacturing processes and quality control
• Patient genetic polymorphisms
• Co-administration with other vaccines

Correct Answer: Manufacturing processes and quality control

Q18. An immunization error-related reaction is defined as a reaction that occurs due to:

• A natural progression of the disease prevented by the vaccine
• Incorrect handling, storage, preparation, or administration of the vaccine
• An unavoidable allergic reaction to vaccine antigen
• Antigenic mismatch between circulating strain and vaccine

Correct Answer: Incorrect handling, storage, preparation, or administration of the vaccine

Q19. Which AEFI should be reported immediately to public health authorities?

• Mild transient headache resolving in hours
• Death occurring shortly after vaccination
• Slight local redness at injection site
• Minor fever responsive to paracetamol

Correct Answer: Death occurring shortly after vaccination

Q20. Which commonly used vaccine adjuvant is associated with increased local reactogenicity but good immunogenicity?

• Aluminum salts (alum)
• Polysorbate 80
• Sodium chloride
• Penicillin

Correct Answer: Aluminum salts (alum)

Q21. The most appropriate laboratory method to confirm an immune response to a vaccine is:

• Culturing the vaccine strain from blood
• Measuring specific antibody seroconversion or neutralizing antibody titers
• Complete blood count only
• Electrolyte panel

Correct Answer: Measuring specific antibody seroconversion or neutralizing antibody titers

Q22. Vaccine failure due to antigenic drift is most typically a problem with which pathogen?

• Poliovirus
• Influenza virus
• Mycobacterium tuberculosis
• Clostridium tetani

Correct Answer: Influenza virus

Q23. The best practical methods to prevent cold chain breaches include:

• Using vaccine vial monitors, continuous temperature loggers, and trained staff
• Leaving vaccines at room temperature overnight routinely
• Freezing all vaccines to extend shelf life
• Storing different vaccines together without monitoring

Correct Answer: Using vaccine vial monitors, continuous temperature loggers, and trained staff

Q24. Which type of vaccine formulation is particularly damaged by accidental freezing?

• Aqueous oral vaccines without adjuvant
• Aluminum-adjuvanted (adsorbed) vaccines
• Lyophilized live vaccines that require reconstitution
• Viral vector vaccines stored at −80°C

Correct Answer: Aluminum-adjuvanted (adsorbed) vaccines

Q25. You should suspect secondary vaccine failure when a vaccinated person develops the target infection:

• Within hours of vaccination
• Several years after completing the recommended schedule despite prior protection
• Only if exposed to laboratory-contaminated vaccine
• Only in cases of documented immunization error

Correct Answer: Several years after completing the recommended schedule despite prior protection

Q26. A key criterion in causality assessment for an AEFI is:

• Temporal relationship between vaccination and event
• Patient’s socioeconomic status
• Manufacturer marketing claims
• Historical vaccination rates in the community

Correct Answer: Temporal relationship between vaccination and event

Q27. Which documentation elements are essential to record at the point of vaccine administration?

• Patient diet details and shoe size
• Vaccine name, batch/lot number, manufacturer, expiry date, route, site, and administrator details
• Only the date of visit with no vaccine details
• Brand of non-related medications patient is taking

Correct Answer: Vaccine name, batch/lot number, manufacturer, expiry date, route, site, and administrator details

Q28. Two live attenuated vaccines that are not given on the same day should be separated by at least:

• 7 days
• 14 days
• 28 days
• No separation is ever required

Correct Answer: 28 days

Q29. Which statement about vaccination in pregnancy is correct?

• Live attenuated vaccines are routinely recommended in pregnancy
• Inactivated influenza and Tdap vaccines are recommended during pregnancy when indicated
• All vaccines are contraindicated in pregnancy
• No vaccines provide benefit to the neonate when given to the mother

Correct Answer: Inactivated influenza and Tdap vaccines are recommended during pregnancy when indicated

Q30. Which global organization provides guidelines and tools for AEFI surveillance and causality assessment?

• World Health Organization (WHO)
• Local community health worker groups only
• Private pharmaceutical marketing boards
• International Olympic Committee

Correct Answer: World Health Organization (WHO)

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