This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Systemic Bacteriology (Gram Positive Bacilli, Gram Negative Bacilli), Subject name: Microbiology
The protective titre of antitoxin to diphtheria following vaccination is 
Select and explain. 
A. 0.01 IU/ml, B. 0.05 IU/ml, C. 0.1 IU/ml, D. 0.5 IU/ml
A: 0.01 IU/ml
Answer: A: 0.01 IU/ml 
Explanation: Active immunization by vaccination with diphtheria toxoid is the key in preventing diphtheria. . Serum antitoxin concentration of 0.01 IU/mL is usually accepted as the minimum protective level. 0.01 IU/mL is considered to provide basic protection and 0.1 IU/ml is considered to provide complete or total protection.