Diphtheria is caused by toxin-producing bacteria. WHO says it usually affects the upper respiratory tract and less often the skin. The toxin can damage tissues in the respiratory tract and can also affect the heart and nerves.
How does diphtheria spread?
WHO describes person-to-person spread when an infected person coughs or sneezes. Some infected people may not show manifestations of disease but can still transmit the bacteria. Others develop illness ranging from mild disease to severe complications.
This means symptoms alone cannot identify everyone who may transmit the infection. Investigation of a suspected case and management of close contacts belong with public-health and clinical teams.
What symptoms does WHO describe?
Symptoms usually begin 2–5 days after exposure. WHO lists sore throat, fever, swollen neck glands and weakness among typical symptoms. Within 2–3 days after infection, dead tissue in the respiratory tract can form a thick grey coating over the nose, tonsils or throat, making breathing and swallowing difficult.
A grey coating and difficulty breathing or swallowing are serious findings. They cannot be safely assessed through an article and require urgent professional evaluation.
Why can diphtheria become severe?
The toxin produced by the bacteria causes most severe disease and deaths. WHO lists inflammation of the heart and damage to nerves among the complications. It reports that, among unvaccinated people without adequate treatment, diphtheria can be fatal in around 30% of cases, with children younger than five at greater risk of dying.
This population estimate should not be used to predict the outcome for an individual child. Early recognition and appropriate treatment materially affect risk.
Who is at risk?
WHO says anyone who is not immune because they are unvaccinated or under-vaccinated is at risk. Diphtheria can reappear when population vaccination coverage becomes low. Interrupted health services, overcrowding and poor hygiene can increase the opportunity for infection and outbreaks.
No WHO region is completely free from diphtheria. Areas with low coverage allow the bacteria to circulate, which places unvaccinated and under-vaccinated people at risk.
What does WHO say about treatment?
WHO stresses prompt testing and early treatment when diphtheria is suspected because delay increases the risk of complications and death. Treatment usually includes diphtheria antitoxin and antibiotics. The antitoxin neutralizes toxin circulating in the blood, while antibiotics stop bacterial replication, reduce toxin production and help prevent transmission.
WHO also notes that some strains have shown resistance to antimicrobial medicines. The choice and delivery of treatment therefore require qualified clinical and public-health management; families should not try to select antibiotics themselves.
What happens to close contacts?
WHO says contacts of a diphtheria case should receive preventive antibiotics and have their vaccination status checked. People who are not fully vaccinated should be offered vaccination. These measures are coordinated by health professionals because the definition of a relevant contact and the recommended response depend on the situation.
How does vaccination prevent diphtheria?
Community-wide vaccination with high coverage is WHO’s most effective prevention measure. WHO recommends a full primary series followed by three booster doses through childhood and adolescence to sustain long-term protection. Diphtheria vaccine is commonly given in combination with vaccines against diseases such as tetanus and pertussis.
The exact product and schedule vary by country. Parents should follow the current national immunization schedule and discuss missed doses or contraindications with an appropriate vaccination service.
Why do booster doses matter?
WHO explains that multiple doses and boosters are needed to produce and sustain immunity. Under-vaccination across successive groups of children can permit cases and outbreaks even though a safe and effective vaccine exists.
What do WHO’s coverage figures show?
WHO estimated that 85% of infants worldwide received the recommended three-dose primary series in 2025. That left nearly 20 million infants with no doses or an incomplete series, with substantial differences between and within countries. WHO also reported that national use of all three recommended booster doses was incomplete.
Coverage figures describe populations rather than an individual child’s protection. A child’s vaccination record should be checked against the current schedule used where the child receives care.
Why are surveillance and rapid response important?
WHO connects vaccination with surveillance that can identify and confirm cases and close immunity gaps. When outbreaks occur, it works with countries on response activities and on strengthening routine immunization. These measures help limit spread and protect people who remain susceptible.
When is urgent assessment needed?
Seek urgent medical care when diphtheria is suspected, especially with breathing or swallowing difficulty, a thick coating in the throat, marked neck swelling or serious weakness. Contact the health service before arrival when possible so it can advise on infection-control arrangements. Emergency breathing difficulty requires immediate emergency assistance.
Can a person spread diphtheria without obvious illness?
Yes. WHO states that some infected people may not develop manifestations of disease but can still transmit the bacteria. This is one reason that public-health teams assess contacts rather than waiting for everyone to develop the typical throat findings.
Someone with mild symptoms can also be infected. A family’s observation of symptoms is useful information, but it cannot replace testing, contact assessment or instructions from the health authorities managing a suspected case.
Why is diphtheria described as both respiratory and toxin-related?
The bacteria can infect the upper respiratory tract and produce a thick coating that obstructs breathing or swallowing. At the same time, the toxin can move through the body and damage the heart and nerves. Treating the bacterial infection and neutralizing circulating toxin therefore have different purposes in WHO’s description of care.
Antitoxin works on toxin circulating in the blood; it cannot reverse tissue damage that has already occurred. This helps explain WHO’s emphasis on starting appropriate treatment promptly when the disease is suspected rather than waiting for severe complications.
References
- World Health Organization. Diphtheria, 15 July 2026. Source reviewed 4 October 2026.