UNICEF (search) on Monday confirmed two cases of measles (search) in survivors of Indonesia's tsunami, raising fears that the highly contagious and potentially deadly viral infection could take hold on devastated Sumatra (search) island.

The U.N. children's agency is in the midst of a campaign to vaccinate 600,000 people against the disease, which can be deadly to children if not treated, said UNICEF Indonesia spokesman John Budd. The mass vaccination drive in the Sumatra region began last week and is expected to take three weeks to complete.

Clauvia Hudspeth, a UNICEF official in Banda Aceh (search), said there were two cases of the infection in the province, which was the hardest-hit area in the tsunami zone. She gave no more details.

Measles kills more children than any other vaccine-preventable disease, according to UNICEF.

The virus weakens the immune system and renders children highly susceptible to fatal complications from diarrhea, pneumonia, and encephalitis (search). Children who survive measles can be left with permanent disabilities, including brain damage, blindness and deafness.

Budd, in Jakarta, reported the first case involving a child on Sumatra earlier Monday.

"In this situation, it is deadly to children," Budd said. "But we have to keep this in perspective — it is a single case."

There have so far been no major outbreaks of disease since the Dec. 26 disaster that killed more than 150,000 across southern Asia and Africa — including more than 100,000 in Indonesia.