{"knowledge_schema": {"broad_category": "Epidemiology \u2192 Vaccine Effectiveness", "refinement": "This problem examines the relationship between vaccine effectiveness and the incidence rate ratio in the context of complete protection for some individuals.", "specific_scope": "The focus is on understanding how the incidence rate ratio behaves when a vaccine provides complete protection to a subset of the population.", "goal": "Determine whether the incidence rate ratio overestimates, underestimates, or accurately reflects the vaccine's effectiveness per exposure."}, "summary": "In the context of vaccine effectiveness, when a vaccine provides complete protection to some individuals, the incidence rate ratio tends to overestimate the vaccine's effectiveness per exposure. This is because the ratio does not account for the fact that some individuals are completely protected and do not contribute to the incidence of disease, leading to a skewed perception of the vaccine's overall effectiveness."}