Arizona Measles Outbreak Likely Over

The outbreak of measles in Arizona is likely over.

Health officials counted seven confirmed cases of measles in Arizona stemming from the outbreak at Disneyland late last year and have been waiting over the past three weeks to determine whether anyone else developed measles.

It can take up to 21 days for measles to develop in a person exposed to the disease, and Arizona Department of Health Services director Will Humble said last week that the outbreak was likely over if Valentine's Day came and went without any new cases.

See also: -More Than 1,000 People in Arizona May Have Been Exposed to Measles -Anti-Vaccination Doctor Under Investigation by Arizona Medical Board

No new cases have been reported in Arizona.

However, Humble wrote on his blog last week that public health departments usually wait 42 days to declare an official end to the outbreak. (State health officials weren't available for further comment today due to the holiday.)

Health officials had estimated that more than 1,000 people in the state may have been exposed to the highly contagious disease, including 190 to 195 people exposed at an urgent-care center for children in Mesa.

Most of the people who got measles from the Disneyland outbreak were not vaccinated. Health officials say the vaccine is 99 percent effective.

Humble theorized on his blog why Arizona's outbreak could have ended:

So why didn't we get more cases? It's likely a number of factors can explain it. We know that about 95% of people in a community need to be vaccinated in order to achieve the herd immunity necessary to prevent an outbreak. In Kearny, where one of the measles cases exposed over a thousand people, the community is very well vaccinated (100% of Kindergartners and 97% of 6th graders are fully immunized against measles), which likely helped stop measles in its tracks.

Also, it's possible our known measles cases may have exposed other people several days after they first became sick, when they may have been less infectious, which would reduce the risk of spread. Two of the cases had at least one measles vaccine in the past and may have been less contagious, which might also help explain the lack of cases among thousands of exposed individuals. Finally, timely public health interventions helped to stop the spread. Working together, our county health departments and the healthcare facilities that saw cases put in a tremendous amount of overtime and resources to identify, notify, and follow up hundreds of contacts, vaccinate many of them, limit exposures and monitor them for 21 days.

And although Arizona appears to be out of the woods, the cases stemming from the Disneyland are still a concern in other states.

According to the Centers for Disease Control and Prevention, there are a total of 121 measles cases in 17 states and Washington, D.C., 85 percent of which were linked to the DIsneyland outbreak.

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Matthew Hendley
Contact: Matthew Hendley