The U.S. State Department on Friday night said it had "reason to believe" scientists in Wuhan, China, may have been infected with the coronavirus in the autumn of 2019, but Beijing has worked hard to prevent a transparent investigation into the origins of the virus.
In a statement, the agency indicated it thinks several researchers inside the Wuhan Institute of Virology had symptoms consistent with COVID-19 and other seasonal illnesses.
"The [Chinese Communist Party] has prevented independent journalists, investigators, and global health authorities from interviewing researchers at the WIV, including those who were ill in the fall of 2019," the State Department said. "Any credible inquiry into the origin of the virus must include interviews with these researchers and a full accounting of their previously unreported illness."
The virus was first detected in Wuhan in late 2019 – China confirmed on Dec. 31 that it was treating a pneumonia-like virus.
The first death was reported on Jan. 11.
In March, the South China Morning Post said that the first person infected with the disease may have caught it on Nov. 17, 2019.
By late-March, the U.S. had more confirmed cases than any other country.
The U.S. government said there are still so many unknowns about COVID-19, including whether the outbreak potentially began via contact with infected animals or from a laboratory accident. Accidental lab infections, the State Department noted, have caused previous outbreaks in China.
The ruling Communist Party keeps a tight hold on information and is particularly concerned about possible revelations about its handling of the virus that could open it up to international criticism and financial demands.
China stifled independent reports about the outbreak and has published little information on its search for the origins of the virus.
This week, the World Health Organization sent scientists to Wuhan to carry out an investigation into the origins and spread of COVID-19, after months of back-and-forth discussions with Beijing.
China has firmly rejected calls for an independent outside investigation. The head of the WHO recently expressed impatience with how long China took to make necessary arrangements for the expert team’s visit.
The Associated Press contributed to this report.