How common are measles deaths in the United States as vaccination rates fall?

A fourth person with measles has died in Pennsylvania, the state announced Tuesday — marking the first time in decades the United States has recorded so many deaths in a single year.

Measles deaths have been extremely rare in the United States because most people are protected by a highly effective vaccine. But as vaccination rates decline nationally and measles cases rise globally, experts say the death toll from measles may continue to grow in the United States this year and beyond.