At its core, the resurgence of the once-defeated disease of measles in the US is a failure of communication.

As the number of cases has risen in the United States—which has historically been at the forefront of global-health campaigns—it has also risen around the world. By 2017, the disease that killed half a million people annually at the turn of the century was down to 110,000 cases. Now, the first three months of the year saw a 300 percent increase from the same period a year ago, according to a report from UNICEF.

The global-health organization Gavi ties the issue together, citing a storm of seemingly disparate factors: disinformation campaigns in Europe, a collapsing health system in Venezuela, and pockets of low immunization in Africa. In South Sudan, where hundreds of measles cases have been reported in recent months, efforts to vaccinate people after the country’s civil war appear to have been thwarted because of the difficulty of keeping vaccines cool—not because people are refusing them.

Though the United States’ own outbreaks are unrelated to one another in a physical sense, they are linked to a growing online disinformation movement. In a statement on Thursday, the CDC said the outbreak in New York is significant in part due to “misinformation in the communities about the safety of the measles/mumps/rubella vaccine. Some organizations are deliberately targeting these communities with inaccurate and misleading information about vaccines.”