The outbreak would have to spread continuously for more than a year to undo the U.S.’s achievement.

The number of cases reported in Texas' historic measles outbreak has risen to 663 cases in 26 counties, as of April 29. Of those, 87 patients have been hospitalized, and two school-aged children have died since the outbreak began in January.

The Texas Department of State Health Services reported Tuesday its measles cases, which date back to late January, had grown to 663 cases as of Tuesday, marking a jump of 17 cases since the state’s last update as 87 of the patients have been hospitalized while two school-aged children have been confirmed dead from the illness.