Tsunami-stricken Indonesia has escaped major disease outbreaks so far but hundreds of thousands of people are at high risk due to poor conditions in refugee camps, the World Health Organization said Monday.

Health officials have feared epidemics since the December 26 disaster that may have killed 230,000 people in Aceh province and left hundreds of thousands homeless, forcing them to live in makeshift outdoor camps with poor sanitation.

“It’s too soon to declare any sort of victory, there’s still plenty of threat and we have to be careful because the situation is still precarious,” said Bob Dietz, the WHO spokesman in Aceh.

United Nations officials credited a swift response to the tsunami disaster with preventing epidemics that some feared could cause a second wave of death after the tsunami, in which nearly 300,000 people died or disappeared around the Indian Ocean region.

The tsunami destroyed hospitals and medical clinics and killed doctors and nurses. Refugees camps lack enough toilets and clean water is in short supply, keeping the risk of disease high.

People will remain at risk as long as they are not transferred to shelters with better access to health care, said Eigil Sorensen, the WHO special envoy to Indonesia.

WHO and other international health organizations have said measles and the mosquito-borne disease malaria are the most dangerous illnesses threatening the camp population in Aceh, the province at the northern tip of Sumatra island that bore the brunt of the tsunami.

Measles kills more children than any other vaccine-preventable disease, according to UNICEF. The virus weakens the immune system and children who survive measles can be left with permanent disabilities, including brain damage, blindness and deafness.

Working with the Indonesian Ministry of Health, WHO has launched an intensive campaign to offer measles vaccination in Banda Aceh and surrounding areas, aiming to immunize 65,000 children by the end of this week, said Pem Namgyal, WHO medical officer for vaccine-preventable diseases.

Pools of stagnant water were a common sight in Aceh after the tsunami, which pushed walls of water into coastal cities and towns. Relief workers have been spraying with pesticides to hold down the mosquito population, which raised concerns about outbreaks of malaria and dengue fever.

Health officials said the most prevalent diseases found among Acehnese living in the camps were less deadly illnesses such as diarrhea, respiratory problems and skin infections.

“These are the sort of regular illnesses found in other locations with problems of hygiene, although they are not deadly diseases, but it could potentially lead to more serious problems if there are no efforts to improve the camp conditions,” said Gunawan, deputy chief of Indonesia’s Red Crescent in Aceh.