Public Health – Seattle & King County confirmed a new measles case in a King County adult who was on the same flight as a person previously diagnosed with measles in a case announced October 17.
Health officials believe the individual was exposed during that flight. According to Public Health, the person later visited several public locations while contagious, including Toyota of Renton, Valley Medical Center, YangGuoFu Malatang restaurant, and the Disney on Ice event at ShoWare Center in Kent.
This marks the 12th measles case in a Washington state resident this year. Public Health has also responded to several cases involving travelers visiting King County.
The individual had been vaccinated against measles, Public Health confirmed.
Nationally, about 92% of cases this year have been among unvaccinated people, while 4% had received one dose and 4% had received two doses of the MMR vaccine, according to Public Health.
“While it’s possible for someone who’s been vaccinated to get measles, it’s rare,” Dr. Sandra J. Valenciano, health officer for Public Health – Seattle & King County, said in a statement. “Vaccinated people who get measles are generally less likely to spread it to others and less likely to have severe outcomes. The measles vaccine remains a very effective tool and has been safely used for over 50 years.”
People infected with measles can spread the virus before symptoms or a rash appear. The airborne virus can linger for up to two hours after an infected person leaves an area.
Public Health released a timeline of potential exposure locations and times on its website.
The flight transmission between the October 17 case and the new infection demonstrates measles’ extraordinary contagiousness in enclosed aircraft cabins where recirculated air and proximity to infected passengers creates ideal transmission conditions.
The adult patient’s vaccination status contradicts common assumptions that immunized individuals enjoy complete protection, though breakthrough cases remain rare and typically produce milder symptoms than infections in unvaccinated people.
The public location visits including Toyota of Renton, Valley Medical Center, YangGuoFu Malatang restaurant, and Disney on Ice at ShoWare Center created multiple exposure opportunities affecting potentially hundreds of people at each venue.
The 12th Washington state resident case in 2025 represents concerning uptick compared to typical years when measles cases numbered in single digits or zero, reflecting national trends where declining vaccination rates enable outbreaks.
The traveler cases involving King County visitors complicate contact tracing and containment efforts, as infected individuals from other states or countries may expose local populations before departing, leaving Public Health to manage consequences without jurisdiction over the source cases.
The 92% unvaccinated rate among national measles cases validates public health messaging that immunization remains the primary prevention strategy, with the overwhelming majority of infections occurring in people who declined or delayed vaccination.
The 4% single-dose and 4% two-dose breakthrough case rates demonstrate that while the MMR vaccine provides excellent protection, no immunization achieves 100% efficacy, particularly in individuals with weakened immune responses or waning immunity over time.
Dr. Sandra J. Valenciano’s emphasis that vaccinated people who contract measles are “less likely to spread it to others and less likely to have severe outcomes” acknowledges breakthrough infections while reinforcing that vaccination reduces both transmission and disease severity.
The 50-year safety record cited by Valenciano addresses vaccine hesitancy rooted in misinformation, with five decades of global use demonstrating that MMR vaccination benefits vastly outweigh the minimal risks of adverse reactions.
The pre-symptomatic transmission period where infected individuals spread measles before developing the characteristic rash creates public health challenges, as contagious people unknowingly expose others during the incubation phase when they feel healthy.
The airborne transmission and two-hour lingering capability means people entering spaces recently occupied by measles patients face infection risks even without direct contact, requiring extensive contact tracing beyond individuals present simultaneously with cases.
The Public Health website timeline of exposure locations and times enables potentially exposed individuals to assess their risk and monitor for symptoms, though many people may not check the website or connect their locations to the published list.
The Toyota of Renton visit suggests the patient either worked at the dealership, sought vehicle service, or shopped for a car while contagious, with the commercial setting potentially exposing employees and customers during business hours.
The Valley Medical Center visit raises particular concern given the healthcare setting where immunocompromised patients receiving cancer treatment, organ transplants, or other conditions rendering them unable to be vaccinated face heightened infection risks and severe complications.
The YangGuoFu Malatang restaurant exposure in a dining setting where masks are removed for eating and indoor air circulation spreads pathogens creates ideal conditions for transmission among diners and staff working in close proximity.
The Disney on Ice event at ShoWare Center represents the highest-risk exposure given the large crowds, extended duration, and family audience likely including infants too young for measles vaccination who face the most severe complications if infected.
The ShoWare Center Kent location places a potential mass exposure event in South King County, requiring Public Health to contact potentially thousands of attendees who purchased tickets and may have been present during the contagious patient’s attendance.
The measles resurgence nationally and locally reflects growing anti-vaccine sentiment amplified by social media misinformation, with declining immunization rates particularly in certain communities enabling outbreaks that previously would have been prevented by herd immunity.
Seattle’s international airport and diverse population create ongoing measles importation risks, as infected travelers from countries experiencing outbreaks bring the disease into King County where pockets of unvaccinated individuals enable local transmission.
The adult patient demographic suggests either someone who received childhood vaccination decades ago and experienced waning immunity or someone vaccinated recently who fell into the small percentage experiencing breakthrough infections despite proper immunization.
The October timing for linked flight cases indicates the initial October 17 patient exposed others during autumn travel season, with the new case emerging after the typical 10-14 day incubation period.
