Diphtheria is an acute infectious disease driven by exotoxins released by Corynebacterium diphtheriae following mucosal colonization [1][2]. The pathogen primarily targets the upper respiratory tract, where toxin-mediated tissue destruction facilitates local pathology and potential systemic dissemination [2]. It is classified as a vaccine-preventable bacterial illness whose severity and lethality are directly determined by strain-specific toxin production [1].
Disease overview
BacterialDiphtheria
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Evidence-backed informationEN 6/7 applicable sections · ZH 5/7 applicable sectionsUpdated Sep 3, 2026
Diphtheria is a contagious bacterial infection caused by toxin-producing strains of Corynebacterium diphtheriae [1][2]. While many infections remain asymptomatic or follow a mild course, severe presentations carry substantial mortality risk, particularly among unvaccinated populations [1][2]. Historically widespread before the 1930s, the disease persists globally, with contemporary outbreaks increasingly linked to declining immunization coverage and disrupted health systems [2]. Sustained vaccination programs remain the foundational strategy for population-level control [2].
Read the full clinical and epidemiological profile7
Symptom onset typically occurs two to seven days post-exposure and progresses gradually [1][2]. Initial manifestations commonly feature fever, sore throat, hoarseness, cervical lymphadenopathy, and generalized fatigue [1][2]. Within two to three days, necrotic respiratory epithelium consolidates into a dense, grey pseudomembrane that can mechanically obstruct the airway and impair deglutition [1][2]. Systemic toxin absorption may trigger myocarditis, peripheral neuropathy, renal impairment, and thrombocytopenia, with untreated fatality rates approaching thirty percent in susceptible cohorts [2].
Before the introduction of diphtheria vaccine and widespread vaccination in the 1930s, cases occurred throughout the world, and the disease was a major cause of childhood morbidity and mortality [2][3]. Combination diphtheria vaccines introduced through the Essential Programme on Immunization beginning in 1974 have been estimated to have prevented more than 90% of cases between 1980 and 2000 [2]. No WHO region is completely free from diphtheria, and areas with low coverage of diphtheria toxoid-containing vaccine allow the bacterium to circulate, increasing the likelihood of outbreaks [2]. In recent years, outbreaks have been occurring with increasing frequency despite the availability of a safe and effective vaccine, often when civil unrest interrupts vaccination and healthcare access or when under-vaccination leaves immunity gaps [2][3].
Pathogen dispersal occurs principally through direct person-to-person contact via respiratory droplets generated during coughing or sneezing [2]. Secondary spread is facilitated by contact with contaminated fomites or direct touch of infected cutaneous ulcers [1]. Silent transmission chains are sustained by asymptomatic carriers and chronic colonizers, enabling community-level propagation even in the absence of overt clinical cases [1][2].
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Susceptibility is concentrated among individuals lacking adequate vaccine-derived immunity, including those who are completely unvaccinated or have received incomplete primary series [2]. Elevated exposure probability applies to households and communities characterized by overcrowding and substandard hygiene practices [2]. Structural vulnerabilities further amplify risk in regions experiencing humanitarian emergencies or infrastructure degradation, where routine immunization access is severely compromised [2].
Vaccination with diphtheria toxoid-containing vaccine is the cornerstone of prevention, and currently available vaccines are very effective at preventing disease [2][4]. WHO recommends a three-dose primary series beginning as early as 6 weeks of age, with subsequent doses given at minimum 4-week intervals, followed by three booster doses preferably during the second year of life (12–23 months), at 4–7 years, and at 9–15 years, with at least 4 years between boosters to achieve long-term protection [4]. Combination diphtheria vaccines integrated into national immunization programmes have prevented the great majority of expected cases in recent decades [2]. Because vaccinated individuals can still become colonized and transmit the bacterium, vaccination alone is estimated to interrupt transmission in only about 28% of outbreak settings, so immunization must be paired with case isolation, antibiotics, and—where indicated—diphtheria antitoxin to limit morbidity [3]. Strengthening routine immunization, reaching all children with the primary series plus boosters, and sustaining coverage within primary health care are the central public-health strategies [2][4].
- 1Wikipedia contributors. Diphtheria - Wikipedia [Internet]. Wikipedia. cited 3 Sept 2026.Available from: https://en.wikipedia.org/wiki/Diphtheria
- 2World Health Organization. Diphtheria [Internet]. cited 3 Sept 2026.Available from: https://www.who.int/news-room/fact-sheets/detail/diphtheria
- 3Truelove SA et al. Clinical and Epidemiological Aspects of Diphtheria: A Systematic Review and Pooled Analysis. Clin Infect Dis. 2020 Jun 24. PMID: 31425581. doi: 10.1093/cid/ciz808.PubMed: https://pubmed.ncbi.nlm.nih.gov/31425581/
- 4World Health Organization. Diphtheria [Internet]. cited 3 Sept 2026.Available from: https://www.who.int/health-topics/diphtheria
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Austria
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Chongqing, China
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Shanghai, China
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Xinjiang, China
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Provincial statutory infectious disease monthly report
Zhejiang, China
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Italy
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