A measles outbreak spanning Texas, New Mexico and Oklahoma reached at least 453 cases Friday and might be linked to cases in other states and across borders.

Kansas health officials have confirmed 23 measles cases, marking an outbreak for the state as infections in at least 17 states have led to the most cases in the U.S. in a single year since 2019. The Kansas outbreak is spread across 6 southwest counties,

Texas and New Mexico health departments said on Friday that the number of measles cases in their states rose 20% since their last reports three days ago, as experts warn they expect the outbreak to further spread in coming weeks.

Confirmed measles cases in the US grew by 28% in a week to reach 483 this year, worsening a deadly outbreak that has already surpassed last year’s total.

A measles case was confirmed in a person who traveled to Washington, D.C., on an Amtrak train, according to the D.C. Department of Health.

Those vaccinated in the early years of the measles vaccine might not have full protection against the highly contagious virus.

Kansas and Ohio health officials have confirmed several measles cases among mostly unvaccinated children and adults, as the total number of states reporting measles outbreaks reaches 18.

Measles, one of the world's most contagious illnesses, was declared eliminated from the United States in 2000, several decades after the introduction of a highly effective vaccine.