Texas public health officials on Friday reported an additional 22 measles cases in the ongoing outbreak, for a total of 646 outbreak cases. The state’s Department of State Health Services estimates that one percent of the total cases — or fewer than 10 cases — are actively infectious.

When measles began spreading earlier this year in northwest Texas, it didn't take long for the state to reach 50 cases for the first time in three decades. That milestone was a far cry from the 1,097 measles cases that Texas reported back in 1992,