Years of American-led investment in AIDS programs has reduced the number of people killed by the disease to the lowest levels in more than three decades and provided life-saving medicines for some of the world's most vulnerable people. But in the past six months, the sudden withdrawal of US funding has caused a "systemic shock," UN officials warned Thursday, adding that if the funding isn't replaced, there could be more than 4 million AIDS-related deaths and 6 million more HIV infections by 2029, the AP reports.