After health officials near Portland, Oregon, declared a public health emergency over a measles outbreak that affects mostly young children, the viral infection continues to spread.

Clark County, Washington, identified 34 cases and nine suspected cases; 24 of those are among children younger than 10 years old, officials said Sunday. In at least 30 cases, the infected people were not vaccinated to prevent measles. The immunization status of the other four is not known.

The county has one of the lowest vaccination rates in the state: More than 22 percent of public school students did not complete their vaccinations, The Oregonian reported, citing state records.

Measles is so contagious that 90 percent of unvaccinated people who come in contact with an infected person will get the virus, according to the Centers for Disease Control and Prevention. The virus can spread four days before and after symptoms appear.

Officials identified airports, including the Portland International Airport, health care facilities, schools and churches as locations where people might have been exposed to this outbreak.

More:Measles outbreak grows in area with low vaccination rate, most patients not immunized

The measles two-dose vaccine is 97 percent effective against the virus, according to the CDC.

People infected develop a red spotted rash that starts inside the mouth and spreads all over the body. Symptoms include fevers as high as 104 degrees, cough, runny nose and red, watery eyes.

People choosing not to vaccinate have become a global health threat in 2019, the World Health Organization reported this month. The CDC recognized that the number of children who aren't being vaccinated by 24 months old has been gradually increasing.

Some parents opt not to vaccinate because of the discredited belief vaccines are linked to autism. The CDC said that there is no link and that there are no ingredients in vaccines that could cause autism.

More:These 15 U.S. cities are hot spots for kids not getting vaccines

Contributing: Brett Molina and Joel Shannon. Follow Ashley May on Twitter: @AshleyMayTweets