U.S. public health officials tracked the early cases around the country that followed. But a series of setbacks in the administration’s response — including clunky early testing protocols, slow vaccine distribution, a lack of federal funding to help state and local governments respond to the outbreak, and patchy communication with communities most affected by the virus — allowed the disease to gain a foothold among men who have sex with men, particularly those who have had multiple partners in a short period of time.

Epidemiologists, public health officials and doctors now fear the government cannot eliminate the disease in that community, and they’re warning that they are running out of time to stop the virus from spreading in the U.S. population more broadly.

“We now have so many infections in so many corners of the Earth that it will be very difficult to chase this down with vaccination campaigns,” said Sara Sawyer, a professor at the University of Colorado in Boulder who studies the spread of animal viruses to humans. “Not only do we not have enough vaccines, but if even some people go undetected or don’t have symptoms, they’re going to continue to spread it.”