“This is a real phenomenon. I, myself, personally, am dealing and helping a number of people who have a post-acute COVID-19 syndrome,” Fauci continued in his Jan. 22 appearance. “They are virologically okay. The virus is no longer identified in them, but they have persistence of symptoms that can be debilitating. … It can be really quite disturbing.” Fauci told Maddow that the National Institutes of Health, where he’s director of the Department of Allergy and Infectious Diseases, is making “a major investment in research dollars to try and find out the full extent of this, any hints towards what the underlying mechanisms are, what we can do to treat it”—and he also revealed the most concerning long COVID symptoms. Read on to find out what they are, and for more on staying safe, find out why The Mayo Clinic Warns This One Type of Face Mask Is “Unacceptable.” Extreme fatigue, which can persist for months, was the first symptom that Fauci listed as commonly presenting in these long COVID patients. In a survey by Survivor Corps—a Facebook group that connects COVID-19 survivors with medical, scientific, and academic research communities—led by Natalie Lambert, MD, associate professor at Indiana University School of Medicine, researchers talked to more than 1,500 long-haulers about their symptoms, and fatigue was something 100 percent of them said they experienced. And for more on this symptom, check out If You Feel Tired After This, You May Have Had COVID.ae0fcc31ae342fd3a1346ebb1f342fcb Fauci also listed persistent muscular pain as a long COVID symptom, which was the second most common effect long-haulers reported in the Survivor Corps survey. Nearly 67 percent of those suffering from long COVID experienced this symptom. And for more on the aches that come with the coronavirus, check out Ellen DeGeneres Reveals the “One Thing They Don’t Tell You” About COVID. Patients are also reporting fluctuations in temperature, according to Fauci; 29 percent of those surveyed by Survivors Corp said they experienced fever or chills months after fighting the virus. And for more on what constitutes a fever, find out why Your “Normal” Temperature Is Not Actually 98.6 Degrees, Doctors Warn. The last “disturbing” long COVID symptom Fauci highlighted was brain fog, which The New York Times notes is defined as “troubling cognitive symptoms that can include memory loss, confusion, difficulty focusing, dizziness, and grasping for everyday words.” In the Survivors Corp survey, 59 percent of long-haulers experienced difficulty concentrating, 46 percent had memory problems, and 42 percent were struggling with dizziness. And for more on the signs of long COVID, check out If You Can’t Do This, You May Have Had COVID, New Study Finds.