The U.S. Centers for Disease Control and Prevention's Emergency Operations Center has been moved to Level 1, the agency's highest level, due to the risk of Zika virus transmission in the U.S., officials said today.

The Level 1 activation is "reflecting the agency’s assessment of the need for an accelerated preparedness to bring together experts to focus intently and work efficiently in anticipation of local Zika virus transmission by mosquitoes," the agency said in a statement.

The highest level activation means the CDC staff will work around the clock to combat a critical emergency. The three other Level 1 activations have been to combat Ebola, to combat H1N1 influenza in 2009, and after Hurricane Katrina.

The Zika virus has been spreading throughout the Americas and the World Health Organization has deemed it a "global health threat."

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