Microbiology The protective titre of antitoxin to diphtheria following vaccination is A 0.01 IU/ml B 0.05 IU/ml C 0.1 IU/ml D 0.5 IU/ml 💡 Explanation The protective titre of antitoxin to diphtheria following vaccination is ✓ Correct Answer: A. 0.01 IU/ml