The US Army Medical Research Institute of Infectious Diseases (USAMRIID) at Fort Detrick, Maryland, was briefly shut down in 2019 after an inspection by the US Centers for Disease Control and Prevention (CDC). The lab said that the reason for its shutdown was "ongoing infrastructure issues with wastewater decontamination." The Chinese newspaper doubted the explanation, and said that a June study by the National Institutes of Health's All of Us Research Program suggested that COVID-19 may have been in the US as early as December 2019.
The letter noted that China has allowed Western virologists and US media representatives to visit the Wuhan Institute of Virology, while the US has not followed suit with the Fort Detrick nor shared any data with "countries including China that are independent from US geopolitical influence."
In January, a group of international experts traveled to Wuhan as part of a probe into the origins of COVID-19. The WHO compiled a report, saying that a leak of the new coronavirus from a laboratory in Wuhan, the first hotbed of COVID-19, was unlikely.