The source of the initial Disney theme park exposure was not identified, but specimens from several cases matched with the recent measles outbreak in the Philippines.

According to the Centers for Disease Control (CDC), the measles was a virus nearly all children obtained by the age of 15.

[3][4][5][a] In 2000, the US declared measles as eliminated due to an effective vaccination programme and public health response systems.

[4] Vaccine coverage at a quarter of California schools, including several around the Disneyland theme park, was too low for herd immunity.

[7] By February 11, 2015, the Centers for Disease Control and Prevention (CDC) attributed 125 cases of measles across seven US states, 110 of which were in California, to the outbreak.

[7] Of the other 15 cases linked to the Disneyland outbreak, seven were in Arizona, one in Colorado, one in Nebraska, one in Oregon, three in Utah, and two in Washington.

[9] 12 cases, included in the unvaccinated total, occurred in infants too young to have the vaccine; they relied on herd immunity for protection.

[4] The source of the initial Disney theme park exposure was not identified, but specimens from several cases matched with the recent measles outbreak in the Philippines, but was also detected in at least 14 countries.

[10] To encourage vaccination, Roald Dahl's 1986 "Measles: A dangerous illness" open letter was recirculated as a result of the outbreak.

[4] Among Twitter users, the most common retweet was a post of a Forbes news article that described the outbreak as a "turning point in the vaccine wars.

[4] Several studies subsequently looked at the effect of the Disneyland outbreak on people's views about vaccination.