Diphtheria toxin–mediated disease most commonly affects which age group?

• A. Under 1 year
• B. Over 60 years
• C. 1-10 years
• D. 11-20 years

Answer: (C)

Diphtheria toxin–mediated disease shows a pattern where susceptibility is driven by vaccination status and duration of protective immunity. The vaccine is given in infancy with boosters, so protection is strongest in those who have completed the vaccination series and received boosters. When immunity is incomplete or waning, young children are the most at risk. In populations with vaccination, the highest incidence tends to be among school-age children, roughly five to nine years old, which falls within the broader 1–10-year range. Infants under one may still have some maternal protection, and older children and adults often have booster-induced or prior exposure–related protection, making them less commonly affected. Therefore, the age group most commonly affected is the 1–10 years range.