The Oregon Health Authority (OHA) and Clackamas County warned that a measles exposure at Kaiser Permanente's Mt. Talbert Medical Office may have affected visitors Saturday, Aug. 29.

Anyone on the first floor of the office at 10100 S.E. Sunnyside Road in Clackamas between 10:31 a.m. and 6:07 p.m. that day should check their vaccination records and watch for symptoms, officials said Wednesday, Sept. 2, according to OregonLive.

The warning arrives as area families send children back to school. The West Linn-Wilsonville School District opened its year Sept. 1, according to the Wilsonville Spokesman. Lake Oswego High School students return Tuesday, Sept. 8, per the school's calendar.

Oregon has recorded 50 measles cases so far in 2026, according to OHA. The Mt. Talbert alert came one day after officials announced possible exposures at three Legacy Health facilities in Multnomah County.

Dr. Brad Olson, a Legacy Health pediatrician, said the return to classrooms raises the stakes because the virus spreads quickly among people who are not immune.

"People should prepare for a surge of measles cases this winter, unfortunately," Olson told OregonLive. "Everyone who's eligible for the measles vaccine should get it and should get it now."

An unvaccinated person exposed to someone with measles has about a 90% chance of becoming infected, Olson said. The virus can linger in the air for up to two hours after an infected person leaves a room. Someone with measles can spread it starting four days before the rash appears.

Symptoms show up seven to 21 days after exposure. They often begin with fever, cough, runny nose and red eyes. The rash comes several days later.

Two doses of the measles, mumps and rubella (MMR) vaccine are about 97% effective. An MMR shot given within 72 hours of exposure can reduce the severity of illness, Olson said.

After that window, the vaccine cannot change the course of infection from that exposure.

OHA said parents may want to consider an early MMR dose for infants while measles circulates in Oregon. Babies can receive the shot as young as 6 months old.

Children vaccinated before their first birthday still need two additional doses after turning 1.

People born after 1957 who have never had measles and have not been vaccinated should get the MMR vaccine as soon as possible, OHA said.

Anyone who develops symptoms within three weeks of a known exposure should call a health care provider before visiting a clinic or hospital. That gives staff time to isolate a potentially infectious patient.

Measles can cause pneumonia, brain swelling and death. Infants, children younger than 5, pregnant people and those with weakened immune systems face the highest risk. The U.S. has recorded more than 2,900 cases in 2026, the most in 35 years, according to CDC data cited by OregonLive.