Measles continues to spread across the country. And as Arizona kids are preparing to head back to school, classroom vaccination rates remain below the recommended threshold for herd immunity.
The MMR vaccine is highly protective against measles. According to the Centers for Disease Control and Prevention, two doses of the vaccine are 97% effective at blocking the virus.
But measles is so contagious that medical experts say about 95% of the population must be vaccinated to prevent its spread. Arizona kindergarteners have not had that level of vaccination since the 2010-2011 school year, according to the Arizona Department of Health Services. As of the 2023-2024 school year, the latest year for which data is available, the kindergarten vaccination rate statewide had fallen to 88%.
And Dr. Bob England, former director of Maricopa County Public Health, said that’s an average, so many schools in the state fall even shorter of the 95% goal.
“Some schools have more than that 95% threshold, but most of them don’t,” England said. “That means you drop a case of measles into the wrong school, and it’s probably going to take off.”
The Arizona Department of Health Services lists vaccination rates by county and by school on its website.
More than 1,300 cases of measles have been confirmed in the U.S. this year amid a growing outbreak. Just four of those cases have been in Arizona. The vast majority of recent U.S. cases have been among unvaccinated people, according to the CDC.
This year’s case count is now the highest the country has seen since 2000, when the disease was declared to be eliminated in the U.S.
England said school vaccination requirements were critical to achieving that elimination.
“That’s how every state in this country got enough kids immunized that these diseases became largely diseases of the past that people don’t see anymore,” England said. “Schools are where it amplifies.”
But vaccination rates nationwide have decreased in the past 25 years, and the rate of parents seeking exemptions for their children from school vaccine requirements has risen, England said. In Arizona, the trend has accelerated since the pandemic. In the 2019-2020 school year 5.4% of Arizona’s kindergarteners had vaccine exemptions. As of 2023-2024 the state’s exemption rate was 8.7%, the fifth-highest rate in the country, according to KFF.
England urges Arizona parents to follow the two-dose vaccine schedule for measles that doctors have recommended for young children for decades. He said this not only protects individual children, but also helps prevent outbreaks.
“By getting vaccinated and by encouraging parents of the kids around your child to be vaccinated, we’re all helping to protect each other,” England said.
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