SEATTLE — Measles outbreaks in Texas and New Mexico have led to nearly 300 cases and two deaths, raising public health concerns. Isolated cases have also been reported in a number of states, including Washington. Public Health — Seattle & King County last month confirmed a case of measles in an infant who had traveled abroad.

The cases come as public health experts have been increasingly concerned with falling childhood vaccination rates in the past several years, and of a growing anti-vaccination movement in the U.S.

Data from the Washington State Department of Health shows that in 36 of the state's 39 counties, the rate of vaccination against measles among kindergarten students fell from the 2019-20 to the 2023-24 school years.

Kindergartners are required to be fully vaccinated against measles through the MMR vaccine before school begins, though state law allows parents or guardians to claim exemptions for religious or medical reasons. The kindergarten vaccination rate has declined across Washington, and quite sharply in some counties. And in the 2023-24 school year, kindergartners in only one Washington county met the herd-immunity threshold for measles of a 95% vaccination rate. Herd immunity occurs when the rate of vaccinations is high enough to stop an outbreak.

Measles is a highly contagious virus, and it doesn't take much for the spread of the disease to spiral out of control. Fortunately, the measles vaccine is effective at preventing disease, and it also provides long-lasting immunity. The vaccine is given in two shots, the first when the child is 12-15 months old, and the second at 4-6 years old.

King was among the counties where the measles vaccination rate dropped. In the 2023-24 school year, the most recent data available, around 20,500 of the 22,200 kindergartners had received both doses of the measles vaccine, for a rate of 92.2%. That figure has gradually declined since the 2019-20 school year, when it was above the herd-immunity threshold, at 95.6%. King County fell below the 95% mark in the 2021-2022 school year.

Of the more than 1,700 kindergartners in King County listed as not vaccinated against measles in the previous school year, the majority (64%) were out of compliance, meaning they hadn't submitted proof of vaccination and hadn't received an exemption. While 30% had received religious exemptions or religious membership exemptions and 2% had medical exemptions. Around 4% had conditional status, meaning they intended to complete the vaccination requirement but had not done so yet.

Among the school districts wholly in King County, Enumclaw had the lowest rate of kindergarten measles vaccine completions in the 2023-24 school year, at 83.9%. Vashon Island, which has long been known for its low rate of vaccinations, was second lowest, 84.3%, followed by Tukwila at 86.3%.

The Mercer Island School District had the highest rate of kindergarten measles vaccinations in the past school year, at 97.3%, followed by Shoreline at 97.2% and Lake Washington at 96.9%.

Seattle Public Schools was below the 95% herd-immunity threshold at 93.1%. Seattle fell below the 95% mark in the 2021-22 school year.

Measles vaccination rates have fallen sharply in nearly every state since 2020. The decline has been linked to fallout from the pandemic, such as health concerns surrounding the COVID-19 vaccine and a decline in trust of public-health officials.

The biggest decline in kindergarten measles vaccinations among Washington counties was in rural Pend Oreille, in the northeast corner of the state, where the rate fell from 95.1% to 80% — a remarkable 15.1 percentage-point drop. Other large declines were in Pacific County, down 14 points, and Columbia County, down 12.9 points.

Just two counties increased their rate of measles vaccine completions among kindergarten students from 2019-20 to 2023-24. Ferry County, in northeastern Washington, had the biggest jump, up 2.2 points. Even so, it still only had an 86.7% measles vaccination rate in the past school year. San Juan County had a small increase of less than one point.

Data wasn't available for the 2019-20 school year for Wahkiakum County. According to the Department of Health, of the two schools in the county, one failed to report immunization numbers that year, and the other reported numbers with inconsistencies.

Yakima County had the highest rate of kindergarten measles vaccinations in the 2023-24 school year, at 96.4%. It was, in fact, the only county where the rate exceeded the 95% herd-immunity threshold. That's a big change from the 2019-20 school year, when 14 counties were above 95%.

Stevens County, in northeastern Washington, had the lowest rate of measles vaccinations among kindergartners, at 76.9%, and was one of two counties where the rate was below 80%.

The other was Jefferson County, where Port Townsend is located, with a rate of 79.2% in the last school year.

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