On evaluating an influenza vaccine, it demonstrated an efficacy of 95% in randomized controlled trials and an effectiveness of 90% in post-marketing surveillance studies. Which of the following statement is incorrect?

Appeared in: INI-CET EXAM -2026

Explanation

The statement that a vaccine provides 'absolute and complete protection' is incorrect.
Vaccine efficacy and effectiveness are statistical measures of risk reduction, not guarantees of immunity.
A 95% efficacy or 90% effectiveness still implies that a small percentage of vaccinated individuals may contract the disease (breakthrough infection), although it is often less severe.

Option A: This is a correct statement that accurately defines the 95% vaccine efficacy observed in the randomized controlled trial.
Option B: This is a correct statement that accurately defines the 90% vaccine effectiveness observed in real-world, post-marketing studies.
Option D: This is a correct and fundamental principle in epidemiology. Real-world factors almost always result in effectiveness being lower than the efficacy measured in ideal trial conditions.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Difference between Vaccine Efficacy and Vaccine Effectiveness as background academic context rather than a clinical decision trigger.
Nurses play a vital role in public health by educating patients about vaccine benefits and limitations, helping to manage expectations and combat misinformation.
Understanding efficacy vs. effectiveness allows nurses to accurately answer patient questions like, 'If the vaccine is 90% effective, why did my vaccinated friend still get sick?'.
This knowledge is crucial for building trust and encouraging vaccine uptake, which is a cornerstone of preventive medicine and achieving herd immunity.

How to Approach the Question

First, identify the core task: find the INCORRECT statement. This means you are looking for the option that is factually wrong.
Next, define the key terms from the stem: 'Efficacy' (performance in ideal, controlled trial conditions) and 'Effectiveness' (performance in real-world, general population conditions).
Evaluate each option against these definitions. Option A correctly defines the 95% efficacy. Option B correctly defines the 90% effectiveness.
Evaluate Option D, which states effectiveness can be lower than efficacy. This is a known principle in epidemiology and is supported by the numbers given (90% < 95%). This statement is correct.
Finally, evaluate Option C. The words 'absolute' and 'complete' imply 100% protection. Since the efficacy/effectiveness are 95%/90%, this statement is a clear contradiction and therefore the incorrect statement the question is asking for.

Concept Tested & Keywords

Concept Tested: Difference between Vaccine Efficacy and Vaccine Effectiveness
Stem keywords: influenza vaccine, efficacy, effectiveness, randomized controlled trials, post-marketing surveillance
Lead-in keywords: incorrect
Negative lead-in flag: The question asks for the INCORRECT statement, meaning three options are correct facts and one is false.

Q5Ij0OT4ZUa1WvdwOTIbuv

E6 Ghai Essential Pediatrics(pp 26-904 of 913) p. 186-188

E6 Medicine Harrison 22e Part 1 p. 1590-1592

E6 Pharmacology Nursing Lilley 11e Part 3 p. 153-155

Practise the full INI-CET EXAM -2026

Attempt every question from this paper in a timed mock, then review the full solution for each one.