A top official at the National Institutes of Health (NIH) said Sunday that the coronavirus outbreak is “on the verge” of becoming a global pandemic unless containment of the deadly disease becomes “more successful.”

Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, told CBS’s “Face The Nation” that multiple person-to-person transmissions need to occur in multiple countries in order to reach the pandemic threshold.

Fauci said that as of Sunday, 24 countries have more than 500 cases, with several of them reaching the second and third transmission of the virus.

“Technically speaking, the [World Health Organization] wouldn’t be calling this a global pandemic. But it certainly is on the verge of that happening reasonably soon unless containment is more successful than it is right now,” he said.

PANDEMIC FEARS? Dr. Anthony Fauci tells @margbrennan that #Coronavirus is certainly “on the verge” of becoming a pandemic “unless containment is more successful than it is right now.” pic.twitter.com/zOJeaSJk66 — Face The Nation (@FaceTheNation) February 16, 2020

Fauci’s comments come on the heels of announcements that American passengers aboard the Diamond Princess cruise ship are leaving the quarantined vessel. The director confirmed that 40 Americans have tested positive for the virus since they were stuck on the ship.

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Evacuees from the ship who have not tested positive and have not shown symptoms can return to the U.S. and will be subjected to a quarantine of at least 14 days. Those who show symptoms will not be permitted to fly back to the U.S., Fauci said.

The coronavirus has now caused more than 1,600 deaths worldwide, and the U.S. has confirmed 15 cases of the disease.