Diphtheria is a serious infection caused by toxin-producing strains of Corynebacterium diphtheriae that kill healthy tissue, most commonly in the respiratory system [1][3][4]. The bacterial toxin damages the airway lining and can disseminate throughout the body [1][4].
Disease overview
Bacterial Evidence-backed information EN 5/7 applicable sections · ZH 5/7 applicable sections Updated Oct 23, 2026
Diphtheria is a contagious bacterial disease that has largely receded since vaccine introduction but re-emerges where immunization coverage falters [1][2]. Outbreaks have increased in frequency in recent years owing to under-vaccination, and no WHO region is entirely free of the disease [1]. Systematic review evidence indicates a median incubation of 1.4 days and a basic reproductive number of 1.7–4.3, underscoring continued transmission risk [2].
Read the full clinical and epidemiological profile 6
Symptoms generally appear 2–5 days after exposure and often begin gradually with sore throat, fever, and swollen neck glands [1][3][4]. Within 2–3 days, dead tissue may form a thick grey or white coating over the nose, tonsils, and throat, impairing breathing and swallowing and sometimes producing a barking cough [3][4]. Severe disease arises from toxin effects, with rare hematogenous spread causing injury to heart, kidneys, and nerves [3][4].
Diphtheria is a contagious disease caused by toxin-producing bacteria that can spread from person to person via respiratory droplets when an infected person coughs or sneezes, and some infected individuals remain asymptomatic yet still transmit the bacteria [1]. Before the introduction of the diphtheria vaccine and widespread vaccination in the 1930s, cases occurred throughout the world, but the disease all but disappeared following vaccine introduction; no WHO region is completely free from diphtheria, and areas with low immunization coverage allow the bacteria to circulate and increase outbreak likelihood [1]. Recent outbreaks have occurred with increasing frequency due to under-vaccination and civil unrest interrupting healthcare access, and a systematic review of 266 included studies estimated the basic reproductive number at 1.7–4.3, with asymptomatic carriers causing 76% fewer cases than symptomatic ones over the course of infection [1].
The bacterium passes between people primarily through respiratory droplets from coughing or sneezing, and can also spread via direct contact including touching infected sores [1][3][4]. Some infected persons remain without symptoms yet still transmit the organism [1][4]. Vaccinated individuals may become colonized and transmit, so vaccination alone interrupts transmission in only a minority of outbreak settings [2].
Vaccination with diphtheria toxoid–containing preparations is the principal preventive measure and is included in essential immunization programmes everywhere [1][4]. WHO recommends three primary doses beginning as early as 6 weeks of age followed by boosters in early childhood, at 4–7 years, and at 9–15 years, with at least four years between boosters [4]. Three doses are about 87% effective against symptomatic disease and lower transmission by roughly 60%, but because vaccinated persons can still carry and spread the bacterium, isolation and antibiotics remain necessary in outbreaks [2]. Strengthening routine immunization and reaching all children with primary and booster doses is essential to close immunity gaps [1][4].
- 1 World Health Organization. Diphtheria [Internet]. cited 23 Oct 2026. Available from: https://www.who.int/news-room/fact-sheets/detail/diphtheria
- 2 Truelove 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/
- 3 World Health Organization. Diphtheria [Internet]. cited 23 Oct 2026. Available from: https://www.who.int/news-room/questions-and-answers/item/diphtheria
- 4 World Health Organization. Diphtheria [Internet]. cited 23 Oct 2026. Available from: https://www.who.int/health-topics/diphtheria
- A36
- 1C15
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