Once again from the Vanity Fair article:

That fall, the State Department team got a tip from a foreign source: Key information was likely sitting in the U.S. intelligence community’s own files, unanalyzed. In November, that lead turned up classified information that was “absolutely arresting and shocking,” said a former State Department official.

This seems to be a major takeaway from their research. I've looked back over previous articles on the tip off regarding the sick researchers, and I have not yet found a previous mention of the source having such an intimate connection to US intelligence, intimate enough to know what they would probably have in their files.

For example, the Washington Post article of May 23 puts it this way:

WASHINGTON—Three researchers from China’s Wuhan Institute of Virology became sick enough in November 2019 that they sought hospital care, according to a previously undisclosed U.S. intelligence report that could add weight to growing calls for a fuller probe of whether the Covid-19 virus may have escaped from the laboratory.

The details of the reporting go beyond a State Department fact sheet, issued during the final days of the Trump administration, which said that several researchers at the lab, a center for the study of coronaviruses and other pathogens, became sick in autumn 2019 “with symptoms consistent with both Covid-19 and common seasonal illness.”

Then on May 24 the Washington Post gives a bit more information regarding the source:

The Wall Street Journal reported on Sunday that three WIV researchers became ill enough in November 2019 that they sought local hospital care, according to a previously undisclosed U.S. intelligence report, though officials expressed differing views over the strength of the evidence. White House spokeswoman Jen Psaki said Monday the information came from a foreign entity, and that the U.S. needed additional information to independently verify it.
(emphasis added)

The Guardian is vague on the source in on May 24:

China has vehemently denied a Wall Street Journal report citing US intelligence materials that said several members of staff at a key virus laboratory in Wuhan had fallen ill shortly before the first patient with Covid-like symptoms was recorded in the city on 8 December 2019.

So, so far as I can tell, Vanity Fair has given us more than anybody else so far regarding the source of this information. If what Vanity Fair reports is true, we can assume that:
-the source is well known to US intelligence
-the source knows US intelligence operations well
-the source had some sort of regular dealing with US intelligence, OR, the source had knowledge of a stream of US intelligence source and knew what that stream would include

This narrows the field dramatically. If what VF reports is true, this wasn't some nurse tipping them off. Also, it means there may be much more to come.

This also indicates that there was massive coverup in the US, along with, perhaps coordinated with, that in China.