In a dramatic policy shift, Haiti has agreed to support a massive vaccination program to slow a cholera outbreak that has claimed more than 6,000 lives and sickened almost a half-million people.

Beginning in January, Boston-based Partners in Health will provide two dosages of the oral vaccine Shanchol to 100,000 Haitians living in two vulnerable communities: a neighborhood in Port-au-Prince, where potable water and latrines are luxuries, and to an isolated rural village in the lower Artibonite Valley region. The disease outbreak was first detected in the region a year ago this moth.

“We need to bring every resource available to stop the epidemic,’’ said Dr. Paul Farmer, a Harvard University professor who co-founded Partners In Health and serves as deputy U.N. Special Envoy for Haiti.

On the eve of last year’s presidential election, former President René Préval declined to launch a similar vaccination program, fearing social unrest. Government health officials said the program was not adopted because there weren’t sufficent vaccines for everyone.

President Michel Martelly, who was elected in March, and Prime Minister Garry Conille have voiced support for the new vaccination campaign.

“President Martelly is definitely behind the vaccine and so encouraged his ministry of health,’’ said Dr. Louise Ivers, senior policy adviser for Partners In Health. She believes continued deaths and advocacy from health groups helped shape the new policy.

The group is launching the program with Haiti’s health ministry and the GHESKIO Center, a well-respected Haitian aid group known for its groundbreaking work with HIV/AIDS patients in Haiti.

Partners In Health, which spends about $500,000 a month to treat cholera patients, says Haiti’s epidemic is the world’s largest. The decision to vaccinate Haitians comes as the country struggles to bring cholera under control, access to portable water and latrines in the country’s post-earthquake camps sharply decline and as international aid dollars wither.

“There is a steady erosion of support of people coming and leaving,’’ said Farmer, who calls it the “Attention Deficit Disorder” of humanitarian work. “Wavering attention, short cycle of interest.”

Still, getting the international community to pay for the vaccine, which costs $1.85 per dose, remains a challenge. The United Nations has struggled to raise $300 million for cholera outreach in recent months. At the same time, those opposed to vaccinations, are concerned that it will detract from public campaigns for better sanitary measures in Haiti, and from the need to promote potable water and improved sanitary conditions in a country were many people lack both.

A recent a survey of 626 camps with 502,000 homeless quake victims by water and sanitation experts, showed that access to potable water had gone from 48 percent in March to 7 percent in August. Meanwhile, the percentage of camps with available hand washing stations went from, 20 percent to 12 percent during the same period.

Conille, a medical doctor, said tackling cholera is among his top priorities. He wants to launch an army of young Haitians — one for every 200 households — to educate communities about prevention and treatment of waterborne disease.

“I see this, despite the fact that it has had a devastating effect, as an opportunity for us to quickly strengthen our system and address other big public health issues,’’ he said.