Measles Outbreaks and U.S. Elimination Status Under Scrutiny

U.S. officials are currently trying to establish that the measles outbreaks in South Carolina and other states are not connected to last year’s significant outbreak in Texas. This effort is crucial for maintaining the country’s claim of having eliminated the disease, especially after recording the highest rate of confirmed infections in thirty years.

According to the World Health Organization, a country can be considered measles-free only if it has not seen any locally transmitted cases of the same strain for a year or more.

Experts examining this situation suggest that the evaluation of elimination might not be entirely foolproof, as it’s challenging to confirm whether all potential cases related to the Texas outbreak have been accounted for.

A large measles outbreak emerged in Texas at the start of January 2025, subsequently spreading to multiple states, including significant incidences near the Arizona-Utah border and ongoing cases in South Carolina.

In November, the Pan American Health Organization (PAHO), part of the WHO, announced that Canada had lost its measles elimination status after nearly thirty years, mainly due to being unable to control a year-long outbreak of this vaccine-preventable illness.

This year, PAHO will analyze the U.S. measles data, which has reported 2,065 confirmed cases, to determine if the U.S. can continue its measles elimination status held since 2000.

Former public health officials in the U.S. have emphasized that maintaining measles elimination status is a vital measure of national health.

William Moss, a professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health, stated that the U.S. must demonstrate that the current measles cases are unrelated to the Texas outbreak and instead originated from infected travelers.

Public health officials in various states have employed traditional methods, like interviewing infected individuals to trace transmission paths and comparing the viral genotype—part of the virus’s DNA—to establish connections between cases. However, experts argue that this may not necessarily link cases within large outbreaks.

Kelly Oakeson, head of next-generation sequencing at the Utah Public Health Laboratory, pointed out that none of the patients interviewed in Utah reported traveling to Texas or having contact with Texas residents, although they provided incomplete information.

From the state’s thorough genetic testing, Oakeson noted that the measles strain in Utah appears “different enough” from the Texas outbreak, indicating they might not be related.

He mentioned that they don’t believe a direct connection exists, and the state has been collaborating with the CDC and officials from Texas and Arizona to better understand transmission dynamics.

The CDC is also analyzing the complete genetic code of virus samples, a newer method not typically used for assessing measles transmission. Preliminary findings from this CDC analysis suggest that the outbreaks may not be linked, as indicated by two sources familiar with the data.

On December 5, the acting director of the CDC, Jim O’Neill, stated in a post on X that there is no epidemiological evidence connecting the Texas outbreak to the ongoing cases in South Carolina.

A spokesperson for the U.S. Department of Health and Human Services confirmed the CDC’s findings regarding the absence of connections to Texas. However, they noted that many recent U.S. cases share the same genotype without identifiable sources of infection, which might indicate ongoing domestic transmission.

Dr. Noel Brewer, an infectious disease specialist at the University of North Carolina, who has reviewed the CDC’s data, mentioned that early indications point to a halt in new cases in Texas by July, followed by a gap of about three weeks before the outbreaks in Utah and Arizona began.

Brewer explained that no definitive cases link the two outbreaks at this point and mentioned his role in an independent committee tasked with analyzing U.S. data and reporting to PAHO regarding the U.S. evaluation.

He pointed out that the CDC’s challenges in establishing links might also reflect the broader circulation of the virus across the U.S., suggesting it’s currently “not possible to track all cases.”

Johns Hopkins’ Moss addressed the many uncertainties in epidemiological data related to U.S. outbreaks, noting that not all cases are identified or reported, leading to missed connections between outbreaks.

Moreover, many larger outbreaks are occurring in communities that might distrust the public health system, which could make individuals less inclined to report cases or cooperate with investigations.

This situation might result in misconceptions about whether two viruses are different when, in reality, it’s just a sampling issue, Moss explained.

Dr. Demetre Daskalakis, the former director of the CDC’s National Center for Immunization and Respiratory Diseases, who resigned last August over concerns regarding U.S. vaccine policies, stated that PAHO will determine the outcome based on the evidence presented.

He noted that if PAHO finds weaknesses in certain data aspects and identifies compelling reasons to believe the U.S. has lost its measles elimination status, it could indeed mean that status has been lost.