COLORADO, USA — One of the nation’s largest measles outbreaks is unfolding in parts of southwestern Utah and northwestern Arizona, NBC News reports .

Health authorities in Utah have confirmed 23 cases, all but one involving unvaccinated, school-age children. In neighboring Mohave County, Arizona, officials have reported 42 cases they believe are tied to the Utah outbreak.

Health officials in both Arizona and Utah are urging parents to get themselves and their kids up-to-date on the measles vaccine.

The Centers for Disease Control and Prevention calls measles one of the most contagious viruses in the world, and public health experts warn it spreads quickly among people who are not vaccinated.

An NBC News investigation conducted in collaboration with Stanford University found that mu

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