Hanoi  - Low vaccination rates in Vietnam decades ago are behind an unusual outbreak of measles among adults, a government official said Friday.

About 150 people have been hospitalized since late December and up to 10 were in critical condition in Hanoi and surrounding provinces.

Nguyen Huy Nga, head of Vietnam's Department of Preventive Medicine, said that while measles usually strikes children, none of the patients in Vietnam were under 15.

"About 20 or 30 years ago, very few Vietnamese people were vaccinated," Nga said. "Now, when they grow up, they encounter the germs."

Nga said vaccination rates had been especially low in rural and mountainous areas and some of the victims were students from such areas who moved to Hanoi and became infected.

Universal vaccination campaigns in recent decades in Vietnam have prevented measles outbreaks. But Nga said some of this year's victims had been vaccinated as children, indicating the duration of inoculations was not as long as expected.

The Vietnamese newspaper Tuoi Tre (Youth) reported this week that the outbreak was the worst in 29 years. Several patients in Hanoi have developed complicating infections, including meningitis and encephalitis.

The National Institute of Hygiene and Epidemiology (NIHE) and Hanoi's Department of Health held a meeting Thursday on measures to combat the disease.

Institute head Nguyen Tran Hien was quoted by the Vietnamese press as saying that vaccinated children and adults are safe and only adults who knew they had never been inoculated and had not had the disease should seek vaccinations.

Measles is an extremely contagious disease that spreads through respiration. Symptoms include fever, cough, runny nose, red eyes and a bright red rash covering the entire body.

In developed countries, the disease is rarely fatal, but because of its high rate of contagion, vaccination is considered important.

The fatality rate in underdeveloped countries can be high, and recent vaccination campaigns in Africa are credited with saving hundreds of thousands of children's lives per year. (dpa)