Measles is unbelievably contagious — and so far in 2018, people in 21 states have reported cases of the viral respiratory illness.

Between January 1 and July 14 of this year, 107 people in 21 states — plus the District of Columbia — were reported to have measles, according to a Centers for Disease Control and Prevention report released Wednesday.

These are the states affected by the measles outbreak:

  • Arkansas
  • California
  • Connecticut
  • Florida
  • Illinois
  • Indiana
  • Kansas
  • Louisiana
  • Maryland
  • Michigan
  • Missouri
  • Nevada
  • New Jersey
  • New York
  • North Carolina
  • Oklahoma
  • Oregon
  • Pennsylvania
  • Tennessee
  • Texas
  • Washington
  • The District of Columbia
Measles positivepinterest
jarun011//Getty Images


What is measles?

Measles is an acute viral respiratory illness, according to the CDC. It's spread through the air, meaning coughing and sneezing can pass the virus from one person to the next.

Symptoms of measles include high fever, coughing, stuffy nose, and a rash that spreads from the head all the way down the body. "Patients are considered to be contagious from four days before to four days after the rash appears," the CDC says.

Here's the good news: The measles, mumps, and rubella (MMR) vaccine is incredibly safe and effective. One dose is around 93 percent effective; two doses, per the CDC's recommendations, are around 97 percent effective.

Measles outbreaks in previous years

The U.S. has seen 107 measles cases in the first seven-and-a-half months of 2018, which seems high compared to previous years: There were 118 cases in all of 2017; 86 cases in 2016; and 188 cases in 2015.

But it's nothing compared to what happened in 2014, when the U.S. experienced a record-setting 667 measles cases in 27 states — "the greatest number of cases since measles elimination was documented in the U.S. in 2000," according to the CDC. (The virus was declared eliminated thanks, in part, to the country's vaccine program.)

In prior measles outbreaks, most people who got sick were unvaccinated.