With suspected cholera cases in Yemen nearing one million, the WHO is now reporting an outbreak of another deadly disease—diphtheria.

While diphtheria is endemic in Yemen—with an average of 50 suspected cases annually—the disease has recently made an “alarming comeback in the war torn country.” In the last three months, nearly 200 people have been clinically diagnosed and 20 people have died--mostly children and young adults. According to one WHO report, 15 cases received 2 doses of diphtheria vaccine (the WHO recommends 3 doses of the diphtheria toxoid vaccine followed by a booster), 8 cases received one dose, and the remaining cases “did not have any vaccination history.” Thirteen of 21 governorates have been impacted, and the WHO has warned that the outbreak is “spreading fast,” emphasizing the importance of unhindered access to ports so that medical supplies can continue to be brought in.

Yemen—the Current Situation

Yemen is currently in the midst of what the UN has labeled the world’s worst humanitarian crisis, with 17 million people in need of food and many hospitals on the brink of collapse. A brutal civil war has hindered access to clean water and sanitation services, fueling a cholera outbreak that has seen 959,810 suspected cases—over half of which are under the age of 17—and has killed over 2,200 individuals. Now, a three-week military blockade of sea and airports has made a dire situation worse, delaying a WHO delivery of 17 tons of medical supplies, which finally arrived in Sana’a—the largest city in Yemen—on November 27th. Among those medical supplies are 1,000 vials of diphtheria antitoxin, which are needed to treat the rising number of suspected diphtheria cases.

What is Diphtheria?

Diphtheria is caused by the bacterium Corynebacterium diphtheriae, and is primarily transmitted from person to person via respiratory droplets, but can also be transmitted through touching open sores of someone with diphtheria, or by fomites (ie., objects with the bacteria on them). Once infected, the bacterium produces an exotoxin that interferes with protein synthesis in a variety of different cell types, including nerve and muscle cells, leading to cell damage and death. Symptoms include weakness, swollen glands, sore throat and fever. Severe inflammation and the formation of a pseudomembrane in the nose and throat can lead to airway obstruction, and systemic absorption of the toxin can lead to serious complications such as myocarditis, polyneuritis, and renal failure. Treatment includes the administration of antitoxin and antibiotics, as well as isolation of the individual until they are no longer contagious.

Early treatment of diphtheria with antitoxin is critical, as mortality increases from 4% in those treated within 24-48 hours of the onset of illness to 16.1% at 72 hours. However, no antitoxin was available before the WHO delivery on Monday, and its delay likely facilitated at least some of the 20 deaths. Additionally, the disease can easily be prevented by the diphtheria vaccine. However, the vaccine has been in short supply in Yemen. While a vaccination campaign targeting 300,000 children began in late November—with plans to scale up to 3 million children and young adults in December—the ongoing conflict is likely to complicate efforts.

Diphtheria—Other Outbreaks

In the past, diphtheria had been a major cause of morbidity and mortality in children, with up to half of all those infected dying prior to the availability of treatment. Use of the vaccine has nearly eliminated the incidence of disease in some countries—for example, the US recorded 206,000 cases in 1921 before the widespread use of vaccines, but has reported less than 5 cases in the past decade. However, cases continue to occur globally, with 7,097 cases reported to the WHO in 2016, and diphtheria is a “significant child health problem in countries with poor EPI (expanded programme on immunization) coverage.”

Yemen has seen an outbreak of diphtheria before—in 1981-1982, an outbreak led to 149 cases. One of the stated risk factors during this outbreak was low community vaccination coverage. Other countries have also seen diphtheria outbreaks in the past few decades, including India and a massive epidemic in countries of the former Soviet Union. This epidemic primarily affected adults, who had been vaccinated as children but, due to waning immunity and lack of adult revaccination, had become susceptible to infection. Contributing factors included disruption of vaccine supply during the breakup of the Soviet Union, crowded urban populations, and population movement. One prospective case control study following the reemergence of diphtheria in the Republic of Georgia found that lack of diphtheria immunization “was the strongest risk factor for diphtheria.” Earlier this year, a diphtheria outbreak was reported in Venezuela “amid a major economic crisis that has sparked shortages of basic medications and vaccines.”

What is next for Yemen?

Cholera often accompanies conflict situations, as the major risk factors of this disease—including water contamination and population dislocation—are often present during conflict. However, protracted conflict like the situation in Yemen often leads to the “breakdown of health systems, flight of trained staff, failure of existing disease control programs, and destroyed infrastructure,” leaving populations more vulnerable to diseases such as diphtheria due to poor vaccine coverage. As the situation becomes bleaker and bleaker in Yemen—and if critical supplies such as vaccines continue to be blocked by military forces—it is likely that more and more vaccine-preventable diseases will continue to arise.

Outbreak Observatory aims to collect information on challenges and solutions associated with outbreak response and share it broadly in near-real time to allow others to learn from these experiences in order to improve global outbreak response capabilities.

Photo: Petri dish with a mixed culture of Corynebacterium diphtheria

Photo courtesy of CDC/ Dr. Theo Hawkins