The United States is working to drill down on whether outbreaks of measles are related, officials with the World Health Organization said on April 23.
U.S. officials are carrying out whole genome sequencing from samples to try to figure out whether the 2025 outbreak that spread in Texas is linked to other outbreaks, including an ongoing outbreak in Utah, the officials with the organization, known as the WHO, said at a press briefing.
"This is not something easy," Daniel Salas, executive manager of an immunization program at the Pan American Health Organization, a regional WHO office, said, adding: "There is no country that has done this before."
The WHO in 2000 declared measles to be eliminated in the United States. That designation, which means that measles does not spread in a sustained fashion across 12 months, has held to the present day.
Chains of measles transmission have been spreading for months across various parts of the world since early 2025. The WHO's Pan American Health Organization has already removed the measles elimination designation from Canada due to the ongoing transmission.
The U.S. Department of Health and Human Services said when the postponement was announced that U.S. officials requested it to allow more time to analyze measles data, including genomic sequencing.
Jarbas Barbosa, director of the Pan American Health Organization, said during Thursday's briefing that sustained transmission can appear to happen if there was one outbreak in one state, followed by a second outbreak in another state, and a third outbreak in a third state.
"But you need to review the case[s] to see if all these outbreaks are epidemiologically linked," Barbosa said.
Officials also provided more details on the work the United States is carrying out.
Salas said that with the sequencing, the United States "is trying to find the blanks that that may exist between the southeast outbreak, the initial southeast outbreak that was closed—I mean it is closed, they're having a new one—and the outbreak[s] in Utah and South Carolina."
He added: "There is not enough information about the ... tracing of context that can eventually link that. So they're trying to eventually—this is not something that has been done before—they're trying hard to find mutations in that other part of the virus that we usually do not analyze, so that they can eventually ... show that the outbreaks are linked or not."
The CDC declined to provide comment by time of publication.
South Carolina officials said during a separate briefing this week that there is no reason to believe the outbreak in the state was related to other outbreaks in the country.
A spokesperson for the Utah Department of Health and Human Services told The Epoch Times in an email in January that most of the cases in Utah did not have a direct link to other outbreaks, such as the one in Texas.
"While two early Utah cases were genetically similar to the Texas strain, they did not result in further transmission," the spokesperson said. "More recent sporadic cases appear genetically closer to those identified in Colorado and North Dakota."