"The U.S. government has reason to believe that several researchers inside the WIV became sick in autumn 2019, before the first identified case of the outbreak, with symptoms consistent with both COVID-19 and common seasonal illnesses."
US government had many perverse reasons to believe things that turned out to be false.
I'm putting exactly zero trust in what US government says about what happens or happened in other countries especially those deemed by them as adversarial.
And even if such thing happened it's way more probable that it was just common seasonal illness.
No on-the-ground analysis has been allowed in China.