Three researchers from China's Wuhan Institute of Virology (WIV) sought hospital care in November 2019, months before China disclosed the COVID-19 pandemic, the Wall Street Journal reported, citing a previously undisclosed US intelligence report.
The newspaper said the report - which provides fresh details on the number of researchers affected, the timing of their illnesses, and their hospital visits - may add weight to calls for a broader probe of whether the COVID-19 virus could have escaped from the laboratory.
The report came on the eve of a meeting of the World Health Organization's decision-making body, which is expected to discuss the next phase of an investigation into the origins of COVID-19.
A US National Security Council spokeswoman had no comment on the Journal's report but said the Biden administration continued to have "serious questions about the earliest days of the COVID-19 pandemic, including its origins within the Peoples Republic of China."
She said the US government was working with the WHO and other member states to support an expert-driven evaluation of the pandemic's origins "that is free from interference or politicization."
"We're not going to make pronouncements that prejudge an ongoing WHO study into the source of SARS-CoV-2, but we've been clear that sound and technically credible theories should be thoroughly evaluated by international experts," she said.
The United States, Norway, Canada, Britain and other countries in March expressed concerns about the WHO-led COVID-19 origins study, and called for further investigation and full access to all pertinent human, animal and other data about the early stages of the outbreak.