Oregon measles outbreak grows to 25 cases in 3 counties

Oregon health officials said Thursday a Willamette Valley measles outbreak has grown to 25 residents — all unvaccinated.

The outbreak is unusual, despite the highly contagious nature of the disease, in part because it is easily controlled through vaccination. But vaccination rates have declined in recent years, health officials say, leading to repeated outbreaks.

The latest outbreak emerged two months ago, when the state reported that an unvaccinated adult contracted the virus in Marion County. The adult then spread measles to an unvaccinated child in the same household.

To date, there are 16 cases in Marion County, eight in Clackamas County and one in Multnomah County, according to Dr. Paul Cieslak, medical director at the Oregon Health Authority. Five of those cases involve adults over 20 years old, while the rest are under 20, he said.

The outbreak is now the state’s largest since 2019, Cieslak said. That year, the state confirmed 28 cases. (Clark County, just across the Columbia River, saw a “much larger outbreak” that year, he added.)

Measles is a highly infectious virus that spreads through the air and can linger for up to two hours after someone who is infectious has left the area, according to health authorities. People are contagious with measles for up to four days before a rash appears and up to four days after. That means a person might not yet know that they have measles and can unknowingly transmit it to others.

Symptoms include fever, cough, runny nose and red eyes, usually followed by a rash that starts on the face and spreads to the rest of the body. These symptoms begin seven to 21 days after exposure to the infection.

Officials said the spread of measles — which can be fatal — poses the highest risk to those who have not received a measles vaccination, pregnant people, infants younger than 1, and people with weakened immune systems.

Before the measles vaccine was available, an average of 400 to 500 people died of the virus each year in the United States, according to the Centers for Disease Control and Prevention. In 2000, after three decades of vaccination efforts, the U.S. eradicated the virus.

Cieslak said that before 2019, Oregon’s last measles outbreak was in the 1990s, which he attributes to the state’s “very high vaccination rates and very high population levels of immunity.”

“Unfortunately, we’ve seen an erosion in the percentage of people who are getting vaccinated against measles,” he said.

Last school year, Oregon had the second highest non-medical exemption rate in the country, according to the Centers for Disease Control and Prevention. Officials say the measles-mumps-rubella vaccine is highly effective against measles, but only if enough people are vaccinated.

Before 2000, about 1% of the state’s kindergartners would obtain a nonmedical exemption from school vaccination required, according to Cieslak. But that number has steadily risen, he said. Nearly 9% of the state’s kindergarteners during the last school year had a nonmedical exemption.

“That is threatening our herd immunity,” Cieslak said, referring to the prevalence of immunity to a disease across a large population. “Measles is perhaps the most contagious disease that we know of. … It takes very high levels of population immunity in order to stem the transmission of this contagious disease.”

Dr. Sarah Present, health officer for Clackamas County, said large numbers of people who are not vaccinated against measles can put their communities at risk.

“Measles is a serious disease. It’s not just a little rash. There are very frequent complications,” she said. “It can be a significant burden to not be able to go to school when you’re exposed to this illness. Of course, the burden of getting the illness is greater.”

Officials urge people experiencing symptoms of measles to call a health care provider or urgent care center ahead of time to arrange a plan that avoids exposing others in the facility to the disease.

— Kristine de Leon covers the retail industry, small business and data enterprise stories. Reach her at [email protected].

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