GENEVA, SWITZERLAND - A mass vaccination campaign is getting underway to stop diphtheria from spreading among Rohingya refugees in Cox’s Bazar, Bangladesh.

Diphtheria, a disease that was eliminated from Bangladesh decades ago, is rapidly spreading among Rohingya refugees in Cox’s Bazar. The World Health Organization reports more than 110 suspected cases, including six deaths, have been clinically diagnosed.

Health officials warn these cases could be just the tip of the iceberg. They say the refugees are extremely vulnerable to diseases as they have low vaccination coverage and are living in congested, unsanitary settlements that are breeding grounds for infectious diseases.

WHO spokeswoman, Fadela Chaib, said her agency is working with the Bangladesh Ministry of Health and Family Welfare, the U.N. Children’s Fund and partners to contain the spread of diphtheria, a highly infectious respiratory disease. She said this is being done through treatment and prevention.

“For example, WHO assisted for the basic training of vaccinators in several places in Cox’s Bazar for a vaccination campaign targeting all children up to six years with pentavalent DPT vaccine and pneumonia vaccines, which protect against diphtheria and other respiratory diseases,” she said.

The campaign is set to last two weeks. The U.N. reports more than 645,000 Rohingya have fled to Cox’s Bazar since August 25 to escape violence and persecution in Myanmar. Children account for more than half of this refugee population.

As a preventive measure, WHO and partners previously provided more than 700,000 people in Cox’s Bazar with oral cholera vaccine to protect them from that disease. They also recently completed a mass campaign to vaccinate more than 350,000 children against measles and rubella.