A massive, multi-country diphtheria outbreak that has been raging across Sub-Saharan Africa since 2023 has grown large enough to trigger a new Level 2 Travel Health Notice from the U.S. Centers for Disease Control and Prevention, issued June 2, 2026, covering seven countries: Chad, Guinea, Niger, Nigeria, Mali, Mauritania, and Somalia. The notice instructs all travelers to affected areas to ensure they are up to date on diphtheria vaccination before departure — a recommendation that highlights a troubling gap in American adult immunization, since diphtheria boosters are required every 10 years and many adults have not received one since childhood.
The scale of this outbreak is difficult to overstate. From January to November 2025 alone, a total of 20,412 suspected diphtheria cases, including 1,252 deaths, were reported across eight WHO African Region member states — Algeria, Chad, Guinea, Mali, Mauritania, Niger, Nigeria, and South Africa — giving an average case fatality ratio of 6 percent. Several of these countries have been experiencing ongoing outbreaks since 2023, meaning this outbreak has now lasted more than two full years without being contained. Women, children aged 5 to 18 years, and young adults under 30 were the most affected populations, confirming that the immunity gap extends well beyond early childhood.
The WHO's Rapid Risk Assessment, published in March 2026, confirmed that the global risk from this ongoing outbreak is assessed as low for most countries — but specifically flagged the risk posed by international travel of susceptible populations from the WHO African Region. In other words: travelers to these countries who are not fully vaccinated face real exposure risk.
What Diphtheria Is and Why It Was Considered Conquered
Diphtheria is a bacterial infection caused by Corynebacterium diphtheriae, a toxin-producing organism that colonizes the respiratory tract and, in unvaccinated individuals, produces a thick, leathery membrane in the back of the throat and upper airway. This pseudomembrane can grow large enough to obstruct breathing completely, causing suffocation — historically the most common cause of diphtheria death in children. The diphtheria toxin itself, which enters the bloodstream, can cause severe damage to the heart muscle (myocarditis), the nervous system (neuropathy), and the kidneys.
Before the development of the diphtheria antitoxin in 1894 and the introduction of widespread vaccination in the 1920s and 1930s, diphtheria was one of the leading causes of childhood death in the United States. The widespread adoption of the DTP and later DTaP and Td vaccines effectively eliminated endemic diphtheria from the developed world — but elimination requires sustained vaccination coverage. In countries where routine childhood immunization has been disrupted by conflict, poverty, or logistical failure, diphtheria can re-emerge with devastating speed.
The current African outbreak illustrates exactly this dynamic. Laboratory confirmation remained low due to shortages of diagnostic supplies and limited testing capacity. At the same time, the global shortage of diphtheria antitoxin and uneven clinical capacity to provide this essential treatment posed significant challenges for effective case management. The antitoxin shortage is particularly alarming: unlike antibiotics, which can reduce bacterial transmission and are available, diphtheria antitoxin is a biologic product that neutralizes the circulating toxin in the blood. Without it, severe cases cannot be managed adequately even with optimal supportive care.
What Travelers and American Adults Need to Know
For Americans planning summer travel to any of the seven countries listed in the CDC's June 2, 2026 travel notice, the action is straightforward: verify your diphtheria vaccination status before departure. The Td (tetanus and diphtheria) and Tdap vaccines are both available at pharmacies, travel medicine clinics, and primary care offices. Adults who have not received a Td booster within 10 years should receive one before any travel to an outbreak region. The Tdap vaccine is preferred for anyone who has never received it, as it also provides pertussis (whooping cough) protection.
Beyond travel, this outbreak is a reminder that diphtheria vaccination is not a childhood formality — it is an ongoing adult immunization responsibility. A 2025 CDC national immunization survey found that fewer than 60 percent of American adults had received a Td or Tdap booster within the recommended 10-year window. Given that diphtheria has not been eliminated globally, and given that international travel creates real exposure pathways, maintaining adult booster coverage is both a personal and a community-level responsibility.
For those already in outbreak-affected countries, the CDC recommends avoiding contact with anyone exhibiting symptoms including fever, sore throat, difficulty swallowing, change in voice, shortness of breath, weakness, or fatigue. Avoiding touching wounds of others and washing hands frequently are also recommended. Anyone who develops these symptoms after returning from an outbreak area should seek medical care immediately and specifically inform their healthcare provider of their travel history.
Frequently Asked Questions
Q: Which countries are affected by the current diphtheria outbreak?
A: The CDC's June 2, 2026 travel alert covers Chad, Guinea, Niger, Nigeria, Mali, Mauritania, and Somalia. South Africa and Algeria have also reported cases in the broader regional outbreak.
Q: How many people have died in the current diphtheria outbreak?
A: WHO reported 1,252 confirmed deaths among 20,412 suspected cases in Africa from January to November 2025, with a case fatality ratio of approximately 6%.
Q: How often do American adults need a diphtheria booster?
A: Every 10 years with a Td (tetanus and diphtheria) booster. Adults who have never received a Tdap vaccine should get that first, as it additionally covers pertussis (whooping cough).
Q: Is diphtheria a risk in the United States?
A: Endemic diphtheria has been eliminated from the U.S. However, imported cases from travelers remain a risk, particularly in unvaccinated individuals. Vaccination is the definitive protection.
Q: What are the symptoms of diphtheria?
A: Fever, sore throat, difficulty swallowing, a gray or white membrane forming in the back of the throat, change in voice quality, shortness of breath, weakness, and fatigue. Symptoms typically appear 2 to 5 days after exposure.
