She’d heard about the large measles outbreak in northwest Texas. Since January, more than 159 people are known to have been infected, and the outbreak has resulted in two deaths and dozens of hospitalizations.

As measles continue to spread in the U.S., here's who is at risk and who's immune from one of the most contagious viruses in the world.

Philadelphia hospital patients were also warned about possible exposure to the highly contagious virus just days after a warning for Dulles airport travelers.