The fact that some lab researchers were ill before China announced the COVID-19 pandemic was already known, with some experts saying it may have been attributed to seasonal illnesses like the flu.
Information about the researchers was published in The Wall Street Journal on Sunday.
"The most important implications of this would be to show that Wuhan Insititute of Virology director Shi Zhengli was not being truthful when she said that no one in the institute had been ill in that time period", said Jamie Metzl, a senior fellow at the Atlantic Council former national security official in the Clinton administration who has been calling for an investigation into the lab theory.
The virus has so far infected almost 170 million people and killed almost 3.5 million worldwide. Crucially, the new details about the number of researchers, the timing of their illnesses, and their hospital visits come ahead 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 virus origins.
At the briefing, members were asked about the possibility the virus "escaped from a lab". Faced with blistering worldwide criticism that it withheld important information on the novel coronavirus from other countries and the World Health Organization in the initial days of the pandemic, Beijing also pushed an alternative narrative that the virus on in a USA military lab in Fort Detrick, Maryland. Intelligence reporting about possible November infections among Wuhan Institute employees "can't be dismissed" by USA researchers, the source added.
This reporting adds a new level of detail to the information put out in a State Department fact sheet past year, which said the USA had confirmed that researchers at the Wuhan Institute of Virology had fallen ill.
Now, a newly reported USA intelligence, which appeared in the last days of the Trump administration - that embraced and pushed the theory, has found that three Wuhan lab staff became ill with COVID-19 symptoms in November 2019, The Wall Street Journal reported citing a previously undisclosed US intel report.
The classified report is regarded as valid by current US government agencies, experts investigating the origins of COVID-19 and by officials in President Joe Biden's administration. Trump as president referred to the pathogen as the "China virus" and the "China plague".
However, she said the Biden administration continued to have "serious questions about the earliest days of the pandemic, including its origins within the People's Republic of China".
The WHO, which opened its annual ministerial assembly on Monday, has not announced any follow-up to the Wuhan mission but member states may raise concerns in speeches to the weeklong forum.
The demand for more investigation is in stark contrast to the start of the pandemic, when scientists quickly came together around the idea that the virus crossed over from bats via an intermediary animal. U.S. Health and Human Services Secretary Xavier Becerra is due to address it on Tuesday. "We don't feel like that we have that now", Andy Slavitt is quoted by ANI as saying during the briefing.