Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the coronavirus pandemic “devastated the world” in four months and claimed the outbreak “isn’t over yet.”

The virus is “something that’s highly transmissible. ... In a period, if you just think about it, in a period of four months, it has devastated the world,” Fauci said in an interview with the BIO Digital virtual health-care conference on Tuesday. He also described the pandemic as his “worst nightmare” come to life.

“That’s millions and millions of infections worldwide. And it isn’t over yet. And it’s condensed in a very, very small timeframe,” he continued. The virus first appeared in December and has continued to spread in the first half of 2020.

The coronavirus likely originated at an animal and seafood market in the Chinese city of Wuhan. In response, the Chinese government imposed a lockdown in Wuhan and surrounding areas in January.

The virus then spread internationally, with Italy, Iran and South Korea becoming major hotspots in March. The United States now has the most cases of the virus in the world, followed by Brazil and Russia.

As of Tuesday at 4:15 p.m. ET, there are almost 2 million cases of the virus in the U.S. and over 111,000 deaths.

Fauci said the coronavirus is “very different” from Ebola and HIV.

“I mean, Ebola was scary. But Ebola would never be easily transmitted in a global way,” Fauci said. “HIV, as important as it is, was drawn out over an extended period of time. I mean, I think the ultimate impact of AIDS almost certainly will be greater than anything we’re talking about now.”

Ebola has been making a resurgence. As of Monday, up to 12 people have been infected by a new outbreak of Ebola in the Democratic Republic of the Congo. Fauci has worked extensively on HIV research in the early 1980’s.

Countries around the world are currently racing to find a vaccine for the virus. Fauci said last week “we hope to have a couple hundred million doses" by the beginning of 2021.

Remdesivir is the only known drug capable of treating some patients with the virus. Dr. Robert Kadlec, a U.S. Department of Health and Human Services official, told CNN on Monday that the federal government would run out of its supply of remdesivir by the end of the month.

The virus has impacted economies around the world, with countries implementing shutdown orders to prevent the virus from spreading. The International Monetary Fund said in April that the global economy is set to decline an estimated 3% in 2020 amid the pandemic.