Health officials say a suspected measles case in King County has been confirmed.

RELATED: New vaccine from UW could end annual flu shots

Public Health Seattle and King County said Wednesday that the man in his 50s was hospitalized but has been released.

Health officials warn he came in contact with hundreds of people. Doctors say it’s a red alert for anyone in King County who has not been vaccinated against measles.

Officials say the man had recently traveled to Vancouver, Washington, where a measles outbreak is happening, but it’s not clear if that’s where he was infected.

Update: Investigation confirms measles case in King County residenthttps://t.co/2KHdIG9QoS — Public Health – Seattle & King County (@KCPubHealth) January 24, 2019

“Measles is a highly contagious disease and if you don’t have immunity, you can get it just by being in a room where a person with measles has been,” said Dr. Jeff Duchin, Health Officer for Public Health – Seattle & King County. “Fortunately, the measles vaccine is very effective. Two doses of measles, mumps and rubella (MMR) vaccine provides over 95 percent protection against measles and that protection is long lasting.”

RELATED: 23 confirmed measles cases in Clark County, 20 not immunized

Officials have identified several locations in Auburn, Kent and Covington, including two crowded high school basketball games at Kentlake High School on Jan. 10 and 12, visited by the infected person last week. People who visited those locations during the dates and times listed at this link may have been exposed. The measles virus can remain in the air for up to two hours after someone leaves the area.

Health officials in Clark County as of Wednesday said they had confirmed 23 measles cases since the beginning of the year.

The school district there said anyone who even thinks they may have been exposed to any one of the confirmed measles cases to stay away from their campuses, unless they have proof they’ve been vaccinated.

Additional reporting from The Associated Press