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

Abstract

Introduction

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.

Case presentation

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.

Conclusion

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.

Introduction

Diphtheria is an acute toxin-mediated infection caused by Corynebacterium diphtheriae, primarily affecting the upper respiratory tract and characterized by pseudomembrane formation, cervical lymphadenopathy, and potential systemic complications. The widespread use of diphtheria toxoid–containing vaccines has led to a marked decline in global disease incidence, and diphtheria is now considered rare in populations with high immunization coverage [1]. Nevertheless, the disease has not been eliminated and continues to pose a public health threat in low-resource settings.

Protective immunity against diphtheria depends on completion of the primary vaccination series and timely booster doses. Although vaccination is highly effective, immunity may wane over time, and declining antibody levels have been documented years after childhood immunization [2], [3]. Several studies have demonstrated that a proportion of children classified as fully immunized may have suboptimal seroprotection, leaving them susceptible to infection [4], [5].

Breakthrough diphtheria infections in vaccinated individuals, although uncommon, have been reported, including cases occurring in young children [6]. These cases raise important concerns regarding waning immunity, individual variation in immune response, and potential programmatic challenges such as cold-chain disruptions. Overreliance on vaccination history may delay diagnosis, as clinicians may not initially consider diphtheria in immunized patients presenting with sore throat and fever [7].

In resource-limited settings, diagnostic and management challenges are further compounded by limited laboratory capacity, delayed access to specialized care, and constraints in public health surveillance. This report describes a clinically suspected case of diphtheria with microbiological isolation of Corynebacterium diphtheriae in a fully immunized three-year-old child in Somalia, occurring in a resource-limited setting with symptomatic household contacts, and highlights the continued relevance of diphtheria as a differential diagnosis regardless of immunization status.

Case presentation

A three-year-old male child, reported by his caregivers to be fully immunized according to the national Expanded Programme on Immunization, was brought to an outpatient clinic with a two-day history of high-grade fever, sore throat, and poor oral intake. Vaccination status was verified by review of the child’s immunization card, which documented receipt of three age-appropriate diphtheria-containing vaccine doses administered according to the national EPI schedule at 6, 10, and 14 weeks of age. The parents also reported reduced appetite and increased irritability. Two siblings, aged 5 and 7 years, developed similar symptoms during the same period. According to caregiver report and available records, both were age-appropriately immunized.

On examination, the child appeared ill and febrile. Vital signs were otherwise within age-appropriate ranges. Physical examination revealed prominent cervical swelling, producing a characteristic “bull neck” appearance (Fig. 1). Oropharyngeal examination demonstrated markedly hyperemic and enlarged tonsils covered by a thick grayish pseudomembrane that was firmly adherent to the underlying tissue (Fig. 2, Fig. 3). There was no stridor, drooling, or signs of respiratory distress. Cardiovascular, respiratory, abdominal, and neurological examinations were unremarkable.

Fig. 1.

Cervical swelling (“bull neck”) in a 3-year-old child with diphtheria.

Fig. 2.

Oropharyngeal examination of a child showing enlarged tonsils with white-grayish exudates.

Fig. 3.

Oropharyngeal examination of a 3-year-old child showing erythematous and swollen tonsils with adherent white-grayish patches consistent with pseudomembranous pharyngitis.

Initial laboratory investigations showed elevated inflammatory markers, including leukocytosis and an increased C-reactive protein level, consistent with an acute infectious process. Given the characteristic clinical findings and household clustering, diphtheria was suspected. Throat swab specimens were obtained from the patient and his symptomatic siblings. All samples grew Corynebacterium diphtheriae using standard culture and biochemical identification methods available at the reference laboratory. Toxigenicity testing was not available due to local laboratory limitations. Therefore, although Corynebacterium diphtheriae was isolated, the case could not be classified as WHO laboratory-confirmed toxigenic diphtheria.

The child was admitted to an isolation unit to prevent further transmission. Treatment was initiated with intravenous penicillin, along with intravenous fluids for hydration and paracetamol for fever control. Diphtheria antitoxin was not administered because it was unavailable at the treating facility, reflecting a common limitation in resource-constrained healthcare settings. The patient was closely monitored for potential complications, including airway obstruction and cardiac involvement. Clinical improvement was observed within 48 h, with resolution of fever and improved oral intake.

The patient was discharged in stable condition on oral erythromycin to complete the recommended course of antibiotic therapy. Exposed household contacts were given prophylactic erythromycin and advised to seek care if symptoms developed. Microbiological sampling of asymptomatic contacts and systematic review or administration of booster vaccination were not fully feasible because of limited laboratory capacity, lack of toxigenicity testing, and resource constraints affecting follow-up. The family was counseled regarding infection control measures, disease transmission, and warning signs requiring urgent medical attention.

At follow-up three days after discharge, the child and his siblings showed marked clinical improvement, with complete resolution of fever and throat symptoms and no evidence of complications.

Discussion

This case illustrates a rare but clinically significant occurrence of diphtheria in a fully immunized child in a resource-limited setting. Despite the effectiveness of diphtheria vaccination, breakthrough infections continue to occur, emphasizing that vaccination does not confer absolute protection [1], [8]. In this patient, the presence of classical clinical features, including pseudomembranous pharyngitis and cervical lymphadenopathy, was essential for early clinical suspicion and timely diagnosis.

Breakthrough diphtheria in vaccinated individuals has been attributed to waning immunity, individual variation in immune response, and potential programmatic challenges such as interruptions in recommended vaccine storage and transport conditions (cold-chain maintenance), which may reduce vaccine potency before administration, as well as delayed booster doses [3], [5].Serological studies have demonstrated that a subset of children with documented vaccination may lack protective antibody levels, placing them at risk for infection [5]. However, anti-diphtheria antibody titers were not measured in our patient because serologic testing was not available in our setting; therefore, individual seroprotection could not be assessed. Accordingly, waning immunity or suboptimal seroprotection can only be considered possible explanations for disease occurrence despite documented immunization.

Previous reports have documented severe and even fatal diphtheria in fully immunized children, highlighting the danger of excluding diphtheria solely based on vaccination history [6], [7]. Delayed diagnosis may increase the risk of complications and facilitate transmission. In this case, prompt recognition based on clinical findings enabled early isolation and initiation of appropriate antimicrobial therapy, likely contributing to the favorable outcome.

Household clustering of cases, as observed here, reflects the high transmissibility of Corynebacterium diphtheriae in close-contact settings. Early identification, treatment of contacts, and implementation of infection control measures are essential to interrupt transmission, even in vaccinated populations [8]. A key limitation in this case was the unavailability of toxigenicity testing; therefore, despite culture isolation of Corynebacterium diphtheriae, the case does not fulfill WHO criteria for laboratory-confirmed toxigenic diphtheria.

Management of close contacts may differ depending on whether exposure is to toxigenic or nontoxigenic Corynebacterium diphtheriae. Ideally, close-contact management in suspected diphtheria includes clinical monitoring, microbiological sampling of contacts where feasible, antibiotic prophylaxis, and assessment of vaccination status with administration of age-appropriate booster or catch-up doses when indicated. In our setting, not all of these measures were feasible because of limited laboratory capacity, lack of toxigenicity testing, and resource constraints affecting follow-up and vaccination review. For this reason, a pragmatic precautionary approach was adopted, and exposed household contacts were managed as potentially at risk on the basis of clinical suspicion and exposure history. Nevertheless, early administration of appropriate antibiotics and strict isolation remain critical components of care and can significantly reduce morbidity and mortality [1], [9]. In standard practice, close-contact management may include microbiological sampling, antibiotic prophylaxis, and review of vaccination status with administration of age-appropriate booster or catch-up doses when indicated. In our setting, cultures were not obtained from asymptomatic contacts and booster vaccination was not systematically reviewed or administered because of limited laboratory capacity, lack of toxigenicity testing, constrained vaccine access, and follow-up limitations. As a result, contact management was based on a pragmatic precautionary approach centered on exposure history, symptom monitoring, and antibiotic prophylaxis [5], [9].

This case underscores the importance of maintaining clinical vigilance and strengthening surveillance systems in low-resource settings. An additional limitation was the unavailability of anti-diphtheria antibody testing, which prevented assessment of the child’s post-vaccination serologic protection.

Conclusion

This report describes a clinically suspected case of diphtheria with culture-confirmed Corynebacterium diphtheriae in a fully immunized three-year-old child in Somalia. Because toxigenicity testing was unavailable, the case does not meet WHO criteria for laboratory-confirmed toxigenic diphtheria. Despite adherence to the recommended immunization schedule, the child developed classical manifestations of diphtheria, emphasizing that vaccination, while highly effective, does not eliminate disease risk. Clinicians should maintain a high index of suspicion for diphtheria in children presenting with pseudomembranous pharyngitis and cervical lymphadenopathy, regardless of immunization status. Early recognition, isolation, and timely initiation of antimicrobial therapy were key to the favorable outcome observed. Strengthening surveillance systems, ensuring vaccine quality and booster coverage, and improving clinician awareness are essential to prevent diphtheria-related morbidity and transmission in resource-limited settings.

Author agreement

We, the undersigned authors, confirm that:

• 1.This manuscript is original and has not been published previously.
• 2.The manuscript is not under consideration for publication in any other journal.
• 3.All authors have made significant contributions to the work.
• 4.All authors have read and approved the final version of the manuscript.
• 5.All authors agree to its submission and publication in this journal.

CRediT authorship contribution statement

Salad Abdullahi Farah: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation. Abdullahi Hassan Elmi: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Project administration, Methodology, Data curation, Conceptualization. Fartun Abdullahi Hassan Orey: Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Consent for publication

Written informed consent was obtained from the patient’s parents for publication of this case report and accompanying images.

Ethics approval and consent to participate

The case report was prepared in accordance with ethical standards and the principles of the Declaration of Helsinki.

Funding

No funding was received for this work.

Declaration of Competing Interest

The authors declare that there are no known financial or personal relationships that could have appeared to influence the work reported in this case report.