Measles on the rise as immunization rates decline ahead of back-to-school

Last school year, Oregon enrolled more kindergarteners with nonmedical vaccination exemptions than it ever has.

Statewide, almost 9% of kindergarteners had a nonmedical exemption for one or more vaccines required by state law, according to the Oregon Health Authority — marking the second consecutive year of declining immunization rates.

The influx of unvaccinated individuals has contributed to the resurgence of diseases that were previously under control in the U.S. Across the state, Clackamas, Marion and Multnomah counties are currently experiencing outbreaks of measles. And with the first day of school right around the corner, the surge could hardly come at a worse time.

Measles in Marion County

During the 2023-24 school year, about 7% of Marion County kindergarteners were waived from one or more vaccine requirements for reasons unrelated to a medical condition.

This is lower than the state average — as well as the about 10% rates recorded by neighboring Clackamas and Linn counties — but it’s a stark increase from just over a generation ago. In the 2000-2001 school year, only 1.5% of kindergarteners statewide had nonmedical vaccine exemptions.

Vaccination requirements vary by age, but looking at immunization rates among kindergarteners helps health authorities understand trends. Barring documented exemptions, students entering kindergarten are required to have received vaccines for a slew of infectious diseases, such as measles, chickenpox, polio and more.

The effect of declining immunization rates is obvious. As of Aug. 18, Marion County reported 20 of the 30 measles cases in the state. All reported cases have been in unvaccinated individuals, and 23 cases were in school-aged children. Two individuals required hospitalization, but their ages were not announced.

Dr. Paul Cieslak, Oregon Health Authority medical director for communicable diseases and immunizations, said state and county epidemiologists have seen waves of measles cases since about mid-June. This represents the largest outbreak since 2019, when 28 cases were linked to a larger outbreak in Clark County, Washington.

“Before 2019, you have to go all the way back to the early 1990s to see case counts this high,” Cieslak said. “The reason is we maintained 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.”

Community immunity in decline

The vaccine that protects against measles is called the MMR vaccine. It is given in two doses years apart, and also protects against mumps and rubella.

According to the U.S. Centers for Disease Control and Prevention, two doses of the MMR vaccine are 97% effective at preventing measles, and one dose is 93% effective. The target rate for community immunity is about 95% of a population.

Community immunity, which is also known as herd immunity, is the point at which a sufficient amount of the population is immune to a disease that it is unlikely to spread from one person to another. In this scenario, a disease has so little opportunity to proliferate in a population that even individuals who are too young to be vaccinated, have an illness that prevents them from receiving the vaccine or who, in rare cases, the vaccine didn’t work for, are protected.

Community immunity protects everyone, and no one in particular.

Nationally, just over 93% of kindergarteners were vaccinated for measles in the 2023-24 school year – a slight increase from the prior school year. Still, it is the third year in a row that U.S. kindergarteners have been below the target rate of 95%.

In Oregon, the situation has been exacerbated.

In the 2023-24 school year, just under 92% of Oregon kindergarteners were vaccinated for measles. The state has fallen behind national trends for years, but Oregon kindergarteners haven’t been this vulnerable in more than a decade.

While the trend is worrying, there is still some good news — across all grades, 95% of Oregon students have received both doses of the MMR vaccine, and 96% of students have in Marion County.

Nonmedical exemptions on the rise

While state law requires students to have certain vaccines before they can be enrolled in school, certain medical conditions can prohibit individuals from receiving vaccines, or students’ guardians can get a nonmedical exemption.

In Oregon, nonmedical exemptions can be granted by completing an online vaccine education module that takes between 15 minutes to an hour to complete, or by asking a health care provider to sign a vaccine education certificate.

Nonmedical exemptions cover any reason a child’s guardian chooses not to vaccinate, other than a medical condition that prohibits the child from receiving a vaccine. The state doesn’t require guardians to specify the reason they are claiming an exemption, be it for religious purposes, personal beliefs or otherwise.

As overall immunization rates in Oregon have fallen, instances of nonmedical exemptions have increased.

Statewide, more than 7% of kindergarteners claimed nonmedical exemptions for their second measles vaccines in the 2023-24 school year, and just over 6% did in Marion County. While counts of exemptions for medical reasons aren’t vaccine-specific, 0.1% of vaccine exemptions were for medical reasons both state and countywide.

What about Woodburn?

Measles is a highly contagious, airborne virus, and while 96% of K-12 students across all of Marion County have been vaccinated for the disease, outbreaks can still occur when the virus breaks into communities with large amounts of unvaccinated individuals.

Looking only at K-12 schools in Woodburn, including private and charter schools, 91.5% of students have received both doses of the MMR vaccine on average.

Expanding the area to include schools in Mt. Angel, Silverton, Gervais and other nearby cities, about 89% of students between nearly 50 schools have received both doses.

Back to School

With students set to return to school in a few weeks, public health officials are urging parents and guardians “to get their children vaccinated against the highly infectious virus before classes begin,” according to a release from the Oregon Health Authority.

While the OHA and counties are closely monitoring the situation, officials face an uphill battle in trying to contain a measles outbreak.

“Measles is highly contagious and easily transmitted. The virus can remain in the air for up to two hours after an infected person has left the room,” Marion County Public Health Officer Caroline Castillo said. “The best way to protect your family from measles is to get vaccinated.”