PIERRE, S.D. (DRG News) – The number of measles cases in the U.S. this year is approaching levels not seen in 25 years.

The Centers for Disease Control and Prevention says this year’s total is well over 600 cases. The vast majority have been in New York, in populations who typically don’t vaccinate.

South Dakota state epidemiologist Dr. Josh Clayton says measles is a serious, highly contagious respiratory disease.

Clayton says the MMR vaccine is very effective.

He says measles has a low mortality rate.

Clayton says the time between exposure and symptom onset is usually 7 to 14 days.

Nearly half of the states in the U.S. have reported cases of measles, but South Dakota isn’t one of them.