Breakthrough diphtheria in a fully immunized child in a resource-limited setting: A case report from Somalia

Diphtheria is a vaccine-preventable disease that has become uncommon in populations with high immunization coverage. However, breakthrough infections may still occur, particularly in resource-limited settings, posing diagnostic and public health challenges.

We report a clinically suspected case of diphtheria with culture-confirmed Corynebacterium diphtheriae in a fully immunized three-year-old male child from Somalia who presented with a two-day history of high-grade fever, sore throat, and poor oral intake. Two siblings developed similar symptoms during the same period. Clinical examination revealed cervical swelling with a characteristic "bull neck" appearance and a thick gray pseudomembrane covering hyperemic tonsils. Throat swab cultures from the patient and his siblings confirmed Corynebacterium diphtheriae. The child was admitted to an isolation unit and treated with intravenous penicillin and supportive care, followed by oral erythromycin on discharge. Diphtheria antitoxin was not administered due to unavailability. Household contacts received prophylactic antibiotics. The patient and his siblings showed marked clinical improvement without complications. Toxigenicity testing was not available; therefore, the case does not meet WHO criteria for laboratory-confirmed toxigenic diphtheria.

This case highlights that diphtheria can occur despite complete immunization, particularly in resource-limited settings. Clinicians should maintain a high index of suspicion for diphtheria when classical clinical features are present, regardless of vaccination history. Early recognition, isolation, and appropriate antimicrobial therapy remain essential to prevent complications and transmission.