image: Image of Corynebacterium diphtheriae bacteria, a pathogen causing diphtheria by coloured transmission electron micrograph.
Credit: ALFRED PASIEKA/SCIENCE PHOTO LIBRARY
Despite a steady decline in reported cases following a large outbreak in 2022, diphtheria is still being reported in Europe, with the number of cases higher than before 2020. An ECDC Rapid Risk Assessment [1] issued today highlights how ongoing circulation of diphtheria caused by Corynebacterium diphtheriae (C. diphtheriae) may affect some populations who are more vulnerable to infection and recommends tailored public health response measures to protect those most at risk.
A total of 234 cases of diphtheria have been reported across the European Union/European Economic Area (EU/EEA) since January 2023. A significant proportion of these cases has been among people more vulnerable to diphtheria, such as people experiencing homelessness, people residing, working or volunteering in transitional housing centres, migrants [2], and people who use and inject drugs.
‘The fact that we see diphtheria infections acquired by vulnerable populations in the EU/EEA indicates ongoing unnoticed transmission in the community. This is a cause for concern, and calls for more intense efforts to address barriers to vaccination among these vulnerable groups. Effective vaccination programmes have helped to almost eliminate diphtheria, but this also means that healthcare workers may be less likely to recognise the symptoms. Increasing awareness of symptoms, quick diagnosis and prompt public health action are essential’, says Bruno Ciancio, Head of ECDC’s Unit for Directly-Transmitted and Vaccine-Preventable Diseases.
Before 2020, the EU/EEA averaged 21 cases of diphtheria each year. In 2022, 320 cases were reported, many among recently arrived migrants who had been exposed to diphtheria on their journey. Most cases were associated with three sequence types: ST377, ST384 and ST574.
Since the end of 2022, six European countries (Austria, Czechia, Germany, Norway, Poland and Switzerland) have diagnosed 82 diphtheria cases caused by one of the diphtheria sequence types identified during the 2022 outbreak. At least 25 of these cases affected people experiencing homelessness, people who use or inject drugs, people who had not been vaccinated against diphtheria and older adults.
Although ECDC assesses the risk to the general population as very low, thanks to high vaccination coverage against diphtheria in most EU/EEA countries, this risk increases to moderate for groups who are more vulnerable to infection.
If infected, people who have not been vaccinated against diphtheria may present with skin infections or respiratory diphtheria. Respiratory diphtheria can be fatal in 5−10% of cases. In highly-vaccinated populations, most infections are asymptomatic or mild. It is very rare for diphtheria to occur in fully vaccinated individuals and vaccination against diphtheria is part of routine national immunisation programmes in Europe.
The rarity of diphtheria infection and the many ways in which it can manifest mean that clinicians may struggle to identify and diagnose infections. It is essential to increase awareness of diphtheria among clinicians and those working with vulnerable populations to ensure that diphtheria is properly diagnosed and treated, and that cases are notified to public health authorities.
ECDC is issuing the following recommendations to reduce the risk of severe infection in the most vulnerable individuals and to stop the circulation of C. diphtheriae in the community:
- Increase awareness among healthcare workers and people working with vulnerable populations of the various clinical presentations of the illness.
- Apply health promotion activities tailored to populations more likely to be exposed to diphtheria and promote engagement with these groups.
- Ensure equitable access to vaccination including by offering vaccinations to members of groups more vulnerable to infection.
- Regularly assess the availability of diphtheria antitoxin (DAT) for treatment locally/nationally.
- Improve surveillance to promptly detect cases and understand transmission patterns.
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References/notes to editors:
[1] ECDC Rapid Risk Assessment ‘Diphtheria caused by Corynebacterium diphtheriae ST574 in the EU/EEA, 2025’
Available from: https://www.ecdc.europa.eu/en/publications-data/diphtheria-caused-corynebacterium-diphtheriae-st574-eueea-2025
[2] A migrant, as defined by the European Migration Network, is ‘a person who either: (i) establishes their usual residence in the territory of an EU/EFTA Member State for a period that is, or is expected to be, of at least 12 months, having previously been usually resident in another EU/EFTA Member State or a third country; or (ii) having previously been usually resident in the territory of the EU/EFTA Member State, ceases to have their usual residence in the EU/EFTA Member State for a period that is, or is expected to be, of at least 12 months.’ Migrants are therefore a highly heterogeneous group, and it is difficult to generalise about their health and social needs.