Open Outbreak

Diphtheria

Also known as: Corynebacterium diphtheriae, respiratory diphtheria

Diphtheria is a bacterial infection that usually spreads from person to person through close contact and respiratory droplets. It is preventable with vaccines, but outbreaks still happen where routine immunization is weak or disrupted. The illness often starts like a sore throat and fever, then in severe cases forms a thick grey or white coating in the throat that can block breathing. The toxin made by the bacteria can also damage the heart and nerves. WHO says diphtheria is fatal in about 5% to 10% of cases, with higher risk in young children, and that death rates can be much higher where diphtheria antitoxin is hard to obtain. Treatment is urgent: diphtheria antitoxin plus antibiotics, along with supportive care. Recent WHO notices show large outbreaks in parts of Africa and earlier outbreaks in Yemen, Bangladesh, Afghanistan, Laos and Thailand. The main public health protection is high vaccine coverage and fast care for suspected cases.

Key facts

TransmissionPerson to person through close physical contact and respiratory droplets; WHO also notes transmission by direct contact.
Incubationunknown
Case fatalityUsually 5% to 10% according to WHO; can be as high as 40% where access to diphtheria antitoxin is poor.
Reproduction numberunknown
VaccineYes. Diphtheria toxoid-containing vaccines are used routinely and greatly reduce illness and death.
TreatmentPrompt diphtheria antitoxin plus antibiotics; WHO outbreak pages mention erythromycin, amoxicillin and azithromycin in response settings, with supportive care as needed.
ReservoirHumans are the main reservoir for Corynebacterium diphtheriae; WHO outbreak pages also note some disease can be caused by Corynebacterium ulcerans.
Endemic regionsNo single fixed region from the sources. WHO notices in this session describe outbreaks in the African Region, Guinea, Nigeria, Yemen, Bangladesh, Afghanistan, Laos and Thailand, especially where vaccine coverage is low.

Transmission

Diphtheria spreads mainly from one person to another. WHO says transmission happens through close physical contact and through the air in respiratory droplets, such as those released when an infected person coughs or breathes at close range. Outbreak risk rises where many people are unvaccinated, where care is delayed, and where crowded living conditions make close contact common. WHO’s Guinea notice says community protection usually needs very high routine coverage, around 80% to 85%, and that chronically low vaccine uptake can leave whole areas vulnerable. In practice, this means homes, schools, camps, and clinics can all become settings for spread if sick people are not recognized early. The sources used here do not give a reliable single incubation period or reproduction number, so those are listed as unknown rather than guessed.

Symptoms and severity

Diphtheria often begins gradually, with a sore throat and fever. WHO says severe illness can produce a thick grey or white patch at the back of the throat. This can block the airway and make it hard to breathe or swallow. A barking cough and swelling of the neck may also appear. Young children are at higher risk of severe disease. WHO states that diphtheria is fatal in about 5% to 10% of cases overall, and that death rates can rise much higher where diphtheria antitoxin is not available. In the 2023 Guinea outbreak, WHO reported 58 deaths among 538 reported cases by 2023-10-13, and most cases were in children [age] to 4 years. These outbreak figures are not the same as the long-term average risk, but they show how dangerous diphtheria can become when vaccination and case management are weak.

Treatment and vaccines

Diphtheria is a medical emergency. WHO says treatment involves diphtheria antitoxin plus antibiotics. The antitoxin is important because it neutralizes toxin that is still circulating, while antibiotics help clear the bacteria and reduce onward spread. In WHO’s Guinea report, suspected and confirmed cases were treated with amoxicillin and azithromycin, and direct contacts also received antibiotic prophylaxis. In Nigeria, WHO reported laboratory resistance to penicillin in tested isolates from that outbreak, while isolates remained susceptible to erythromycin, which then became the drug of choice there. Vaccine prevention remains the main long-term control tool. WHO repeatedly describes diphtheria as a vaccine-preventable disease and notes that vaccination dramatically reduces illness and death. The literature review returned in this session also supports routine diphtheria vaccination policy. The sources used here do not provide one global estimate of vaccine effectiveness, so none is added.

Where it occurs

Diphtheria can appear anywhere if immunity in the community falls, but recent WHO notices in this session show it is especially affecting places with weak routine immunization, conflict, displacement, or strained health services. WHO reported a large multi-country problem in the African Region in 2025, with suspected cases across eight countries: Algeria, Chad, Guinea, Mali, Mauritania, Niger, Nigeria, and South Africa. Separate WHO notices document outbreaks in Guinea and Nigeria in 2023. Older WHO Disease Outbreak News items in the archive show outbreaks in Yemen and Cox’s Bazar in Bangladesh in 2017, Afghanistan in 2003, and Laos and Thailand in 1996. This pattern suggests diphtheria is not limited to one continent. Instead, it tends to re-emerge where vaccination coverage is too low and public health response is delayed. The sources here support describing recurrent outbreaks, not a fixed modern endemic map.

Recent history

This site’s archive says diphtheria has appeared in 7 WHO notice records since 1996. The older archive items show events in 1996, 2003, and 2017, then a clear return in 2023 and 2025. WHO reported a major rise in Nigeria in 2023, with thousands of suspected cases and a confirmed case fatality ratio of 6.1% in the later 2023 update. WHO also reported an outbreak in Guinea in 2023, with 538 reported cases and 58 deaths by 2023-10-13. The largest recent signal in the sources from this session is the 2025 WHO African Region report: from 2025-01-01 to 2025-11-02, 20,412 suspected cases and 1,252 deaths were reported across eight countries, and WHO noted that several countries had ongoing outbreaks since 2023. Taken together, these notices suggest not a single isolated outbreak, but a broader regional resurgence linked to immunity gaps and limited access to confirmation and care.

What to watch

The main warning sign is spread into new areas with low vaccination coverage, especially if health services are already under strain. WHO’s recent notices repeatedly link outbreaks to under-immunized populations, so falling DTP coverage or missed child vaccination campaigns would be concerning. Another signal is evidence of sustained transmission in crowded settings such as camps, schools, or densely populated districts. Delays in diagnosis matter too, because throat disease can worsen quickly and patients may need antitoxin urgently. Resistance patterns also deserve attention: WHO’s Nigeria report found penicillin resistance in tested isolates and reliance on erythromycin, so any broader resistance to first-line drugs would complicate treatment. Finally, supply problems would raise concern. WHO notes that case fatality can become much higher when access to diphtheria antitoxin is poor. In short, watch for new countries affected, more severe outbreaks in children, reduced vaccine uptake, antibiotic resistance, and shortages of antitoxin or outbreak-response vaccines.

Related outbreaks

Updated