Texas health officials reported 17 new measles cases on Tuesday, bringing the total confirmed cases since late January to 663. The state’s public health department estimates that fewer than 10 of the confirmed cases — about 1% — are “actively infectious.

Nearly all measles infections seen during the Texas outbreak are among individuals who have not been vaccinated, or whose vaccination status is unknown.

As more counties are being impacted by the ongoing measles outbreak and added to the growing list of counties across Texas, here's what to know.