US makes case to maintain measles eradication status as infections rise

By Julie Steenhuysen

CHICAGO, Jan 6 (Reuters) – U.S. officials are building on the possibility that an ongoing measles outbreak in South Carolina and other states is unrelated to last year’s massive outbreak in Texas, as it tries to maintain its status as the disease’s leader after recording the most confirmed infections in three decades.

To be considered measles-free by the World Health Organization, a country must not have locally transmitted cases of the same strain for 12 months or longer.

Scientists studying the issue say eradication assessments may not be ironclad because it is difficult to be certain that all cases potentially related to the Texas outbreak have been reported.

A large outbreak of measles in Texas began in January 2025 and spread to several states, followed by large outbreaks along the Arizona-Utah border and in South Carolina that continue to cause infections.

In November, the Pan American Health Organization — part of the WHO — determined that Canada had lost measles-eradication status after nearly three decades after failing to contain a year-long outbreak of the vaccine-preventable disease.

PAHO will evaluate US measles data this year, which includes 2,065 confirmed cases, to see if it can maintain the measles elimination status it has had since 2000.

Former US public health officials have described measles eradication status as a leading indicator of the nation’s health.

It must be proved that the cases are not related

The United States will have to prove ongoing measles cases are not related to the Texas outbreak, and were instead brought into the country by infected travelers, said William Moss, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.

State public health officials have used traditional methods of interviewing infected people to identify chains of infection, as well as viral genotype — a segment of the virus’s DNA — to see if the cases are related. That still may not be enough to link the cases to a larger outbreak, experts said.

Kelly Oakson, who leads next-generation sequencing at the Utah Public Health Laboratory, said none of the patients interviewed in Utah reported travel to Texas or contact with people in Texas, but many provided incomplete information.

Based on the state’s detailed genetic analysis, however, she said the Utah strain is “different enough” from the Texas outbreak to suggest they are unrelated.

“We don’t think there’s a direct link,” she said in an email, adding that the state is working with the CDC, Texas and Arizona to characterize transmission patterns.

In addition, the Centers for Disease Control and Prevention is analyzing the entire genetic code of virus samples to determine whether the outbreaks are related, a new technique that has not traditionally been used to assess measles transmission.

Preliminary evidence from a CDC analysis, which has not been made public, suggests the outbreaks are unrelated, according to two sources who have seen the data.

In a Dec. 5 post on X, CDC Acting Director Jim O’Neill said there was no epidemiological evidence linking the Texas outbreak and ongoing cases in South Carolina.

A U.S. Health and Human Services spokesperson confirmed that the CDC has found no epidemiological evidence linking the ongoing outbreak in Texas, but that several recent U.S. cases share the same genotype and have no known source of infection, “which may indicate ongoing domestic transmission.”

Possible differences in cases

Infectious disease doctor at the University of North Carolina. Noel Brewer, who has seen CDC data, said preliminary evidence suggests that new cases stopped in July in Texas and that there was a three-week gap before the Utah-Arizona outbreak began.

“None of the cases have linked the two outbreaks in any clear way,” said Brewer, who chairs an independent committee that analyzes U.S. data and reports to PAHO whether it agrees with the U.S. assessment.

The CDC’s inability to link the outbreak, Brewer said, may simply reflect that the virus is spreading widely in the United States and that it is “not possible at this time to track all cases.”

There are many gaps in epidemiologic knowledge of U.S. outbreaks and not all cases are identified or reported, Johns Hopkins Moss said, so you may miss cases linking the two outbreaks.

In addition, many large US outbreaks are occurring in communities that do not trust the public health system and may be less likely to report cases or participate in investigations.

This can lead scientists to falsely conclude that the two viruses are different when it was just a sampling problem, Moss said.

Former CDC director of the National Center for Immunization and Respiratory Diseases, Dr. Demetrius Daskalakis said PAHO will make a call based on the evidence received.

“If they don’t believe the strength of one piece of data, and there are other compelling factors that say America has lost abolition, that means America has lost abolition.”

(Reporting by Julie Steenhuysen; Editing by Carolyn Humer and Bill Berkrot)