Dr. Anthony Fauci, director of the National Institute for Allergies and Infectious Diseases, speaks during a White House press conference chaired by Jen Psaki, White House Press Secretary, in the James Brady Press Briefing Room at the White House January 21, 2021 in Washington. DC.

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New data suggests that people with Covid-19 may continue to experience symptoms for up to nine months after the initial infection, said White House chief medical officer Dr. Anthony Fauci, on Wednesday.

University of Washington researchers recently found that 30% of patients reported symptoms for nine months, Fauci told reporters during a White House news conference about Covid-19. People reported fatigue, shortness of breath, difficulty sleeping and other symptoms that lasted for months, he said.

Symptoms of “long covid,” which researchers now refer to as post-acute episodes of Covid-19 or PASC, can develop “well after” the infection, and severity can range from mild to “incapable,” said Fauci, also director of the National Institute for Allergies and Infectious Diseases.

“The extent of the problem is not fully known,” he said. The addition of PASC has also been reported in people who did not require hospitalization and in people who had symptoms that were not part of their original infection.

The update is released as global medical experts work to better diagnose and treat people with persistent Covid-19 symptoms.

So far, there have been a limited number of studies that have identified what symptoms are most common and how long they might last. The main focus was on people with a serious or fatal illness, not people who have recovered but still report persistent side effects, sometimes referred to as “long distance riders”.

The National Institutes of Health have launched an initiative to study long Covid and identify the causes and possible treatments for individuals, Fauci said. “What makes some people vulnerable while others recover quickly and have no consequences?” he asked.

– CNBC’s Noah Higgins-Dunn contributed to this report.