U.S. health authorities are seeking to demonstrate that recent measles outbreaks in South Carolina and other states are not linked to last year’s major outbreak in Texas, as the country works to retain its measles elimination status.
Under World Health Organization criteria, a country is considered measles-free if it records no locally transmitted cases of the same virus strain for at least 12 months. The United States has held that designation since 2000, despite recording its highest number of confirmed measles infections in three decades.
A large outbreak that began in Texas in January 2025 spread to several states before subsiding. Subsequent outbreaks later emerged along the Arizona–Utah border and in South Carolina, raising concerns among scientists and international health bodies about whether the virus continues to circulate domestically.
This year, the Pan American Health Organization (PAHO), a regional arm of the WHO, will review U.S. measles data involving 2,065 confirmed cases to determine whether the country can maintain its elimination status. In November, PAHO stripped Canada of the designation after a prolonged outbreak of the vaccine-preventable disease.
Also Read:Â US Panel Considers Delaying Newborn Hepatitis B Vaccine
Health experts caution that linking or separating outbreaks with certainty remains challenging. While U.S. officials argue that the newer cases were introduced through international travel rather than domestic transmission, scientists note that incomplete reporting and gaps in case investigations could complicate that assessment.
Public health agencies have relied on patient interviews and genetic comparisons of virus samples to trace transmission chains. Some states have also employed more advanced genetic sequencing to analyse entire viral genomes, a method not traditionally used in measles investigations.
In Utah, officials said genetic evidence suggests the strain circulating there differs from the one identified in Texas. However, researchers acknowledge that incomplete data and underreporting particularly in communities with low trust in public health systems could obscure links between outbreaks.
The Centers for Disease Control and Prevention has indicated that it has found no clear epidemiological evidence tying the South Carolina cases to the Texas outbreak. At the same time, officials noted that several recent cases share the same genotype without a known source, a factor that could point to ongoing domestic transmission.
Independent experts reviewing the data said preliminary findings suggest a gap between the end of the Texas outbreak and the emergence of later cases, though they warned that missing information could still affect conclusions.
