Doctor Nguyen Van Vinh Chau, director of the HCMC Hospital for Tropical Diseases, said the boy, whose name has not been disclosed, was transferred to the hospital at 3 a.m. Sunday, the seventh day after he contracted diphtheria. The disease had triggered heart complications by then. He died 11 hours after being admitted. He had not been vaccinated against diphtheria, Chau said.

The earlier dead victims were a nine-year-old girl and a 13-year-old boy from Dak Nong Province and a four-year-old boy from Gia Lai Province, all in the Central Highlands region hit by the diphtheria outbreak since June.

The HCMC hospital is currently treating two other cases of diphtheria, also from the Central Highlands. The two have been receiving treatment for more than a month and their health condition is now stable.

Vietnam has reported 200 diphtheria cases in the first eight months of this year, mainly in the Central Highlands and the nearby Quang Tri Province in central Vietnam.

Low vaccination rates have been blamed for the repeated incidence of diphtheria outbreaks in the region. The General Department of Preventive Medicine under the Health Ministry said last June the vaccination rate for diphtheria in the Central Highlands was just 48-50 percent, leaving the region susceptible to reoccurring outbreaks.

In Vietnam, children under two are given free five-in-one vaccine shots that include diphtheria.

Diphtheria is an infection caused by the Corynebacterium diphtheria bacterium. It spreads through the air and direct contact.

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