The U.S. Centers for Disease Control and Prevention (CDC) has upgraded its response to the Ebola outbreak to a Level 1 — reserved for only the most serious public health emergencies.

The highest alert, on a 1-6 scale, will allow for hundreds of staff working on other projects to shift focus to the Ebola crisis in West Africa.

The last time a Level 1 response was called was in 2009 during the outbreak of H1N1 flu.

Both Nigeria and Liberia have declared states of emergency over the outbreak.

Officials with the World Health Organization (WHO) said limited medical facilities and remote locations are hampering the battle to control the virus.

The WHO continues its meeting on Thursday to decide whether the crisis — the worst recorded outbreak of its kind –amounts to an international public health emergency.

Meanwhile, two American aid workers sickened by the disease are back in the U.S. and are showing signs of recovery.

A Spanish priest flown home to Spain after contracting the disease in Liberia is the first Ebola case ever treated in Europe.

The Ebola outbreak has killed more than 930 people in the African nations of Liberia, Sierra Leone, Nigeria and Guinea.