Mexican regulators are to approve this week a new vaccine from GlaxoSmithKline against rotavirus, a disease that causes diarrhea and kills up to 600,000 children a year, sources at the international AIDS conference here said on Wednesday.

A company official in London confirmed that a decision was expected “imminently,” after researchers spoke about the landmark approval.

Mexico’s approval of Rotarix, an oral vaccine, would mark the reversal of the history of vaccine development in the last 50 years, in which new products have been launched in the United States and Europe and only later in the developing world.

Medical experts hope its rollout will save hundreds of thousands of lives a year.

The highly infectious disease can cause severe vomiting and diarrhea leading to dehydration. It kills between 400,000 and 600,000 children a year worldwide, mainly in poor countries.

Almost every child is exposed to rotavirus by age five. But 82 percent of rotavirus deaths occur in less developed countries, where children have limited access to healthcare and often arrive at the clinic too late.

The issue of getting medicines to people in the developing world has dominated discussions at the 15th International AIDS Conference in Bangkok, with doctors and policymakers debating the feasibility of rolling out anti-AIDS drugs to millions in need.

In 1998, a rotavirus vaccine marketed in the United States by Wyeth was withdrawn for fears it could cause a sometimes deadly bowel obstruction, causing wariness about the concept and forcing drug developers to conduct much larger safety trials for new vaccines.

Besides GSK, U.S. pharmaceuticals group Merck and Co is also testing a new rotavirus vaccine.