A month before China reported its first COVID-19 cases in 2019, three researchers at Chinas Wuhan Institute of Virology fell ill and had to be hospitalized, according to a previously undisclosed U.S. intelligence report The Wall Street Journal cited on Sunday.

Sick researchers were previously mentioned in a Jan. 15 U.S. State Department fact sheet that didnt say they had to be hospitalized. The fact sheet only stated that researchers had fallen sick in November 2019 with symptoms consistent with both COVID-19 and common seasonal illness and that the Chinese Communist Party had prevented them from being interviewed.

CNN also later confirmed the intelligence reports details, citing two people who were reportedly briefed on the intelligence.