On Feb. 6, Multnomah County health officials sent 5,000 letters to parents, warning that if they do not vaccinate their kids in the next two weeks, they won't be allowed to attend school.

But while Oregon law requires children in preschool and elementary school to be up to date on immunizations, parents can sign non-medical exemptions that allow their kids to forego vaccinations and stay in school.

"As long as they have completed the Oregon process for obtaining a non-medical exemption, these students will be allowed to attend school," says Lisa Ferguson, who oversees the communicable diseases department in Multnomah County.

"The caveat to that," she adds, "is that if there is a measles exposure at their school when they were present and they are not up to date with their MMR [measles, mumps, and rubella vaccine], they would be excluded for 21 days past the exposure."

According the Oregon Health Authority, last year 4,349 children were kept out of school statewide for failing to get vaccinations. The agency sent 24,725 exclusion orders to Oregon parents with unvaccinated children last year.

The year before that, OHA spokesperson Delia Hernandez says, 29,932 letters went home to Oregon parents.

In Multnomah County in 2017, 6,612 exclusion order letters were sent to  parents. In 2018, that number was 5,725.

Hernandez attributes the decline to a 2016 change in Oregon law that says parents seeking non-medical vaccine exemptions for their children must watch an online video or get education from a health care provider.

Before the law change, in 2016, 41,045 Oregon parents were sent exclusion orders—9,899 of those parents were in Multnomah County.

Despite the decrease in unvaccinated children, the region is facing the worst measles outbreak in recent memory. There are now 54 confirmed cases in the Vancouver-Portland area, four of which are in Oregon.

"This year's School Exclusion Day reminder has taken on added urgency as the Pacific Northwest confronts the worst preventable measles outbreak in more than two decades," Stacy de Assis Matthews, school law coordinator for OHA, said in a statement. "Immunizations are the most effective way to stop the spread of measles and other communicable diseases that put children and others at risk."