The evaluation was drawn up by the General Department of Preventive Medicine under the Health Ministry Friday, in accordance with the findings of infection and epidemiology experts.

Tran Duy Hung, head of the Department of General Infectious Diseases under the National Hospital for Tropical Diseases in Hanoi, said diphtheria has been absent in northern Vietnam over the years thanks to the expanded program on immunization.

Yet the disease has not been eliminated in Vietnam, and sometimes still appears in remote areas of the nation, especially in the Central Highlands, he said.

For the past five years, provinces in the region have repeatedly reported cases of diphtheria and related fatalities.

So far this month, Dak Nong Province diagnosed 12 people with the disease, including one patient in critical condition, after a nine-year-old girl died last week.

Last year, Dak Lak Province reported four cases, with one death. In 2018, five locals were diagnosed with the disease in Kon Tum Province, with two reported fatalities.

In 2017, Quang Nam Province, which borders Kon Tum, recorded seven cases, all children, with one death. In 2016, Kon Tum reported a suspected death by diphtheria.

Gia Lai Province in 2015 reported at least five cases and one fatality.

Explaining the current situation in Dak Nong, Nguyen Thanh Truong, deputy director of Ho Chi Minh City Hospital for Tropical Diseases, said: "This is most likely because the vaccination rate in this area is too low."

Health authorities in Dak Nong have also confirmed the vaccination rate for diphtheria in the province falls around 50 percent.

Diphtheria is an infection caused by the bacterium Corynebacterium diphtheria. The disease spreads through either the air or direct contact.

Symptoms include fever, a sore throat, swallowing difficulties and development of white patches in the throat, which could block the airway. Complications include myocarditis, kidney problems, respiratory failure, inflammation of nerves, coma and death.

It is not too difficult to treat patients with diphtheria, as long as they are brought to hospital in time for diagnosing, said Truong.

But the disease can become serious if the bacterium mutates, and once that happens, it could kill the patient in 24-48 hours, he said.

"If vaccinations are well implemented, there would be no outbreaks. What should be questioned here is the preventive medicine performance in localities that have reported outbreaks," he said.

Huynh Minh Tuan, head of the Infection Control Department at the University Medical Center HCMC, said in some cases, adults who had already received vaccinations should repeat the procedure because their immune systems may have deteriorated, making them susceptible to infection.

For now, HCMC is the second locality in Vietnam to report a diphtheria outbreak after Dak Nong, after a 20-year-old man in the city was diagnosed with the bacteria.

Authorities have yet to track down the source of transmission for both the case in HCMC and the outbreak in Dak Nong.