Robert Gallo apologized for still coughing. The day before President Biden tested positive for COVID-19, the famed HIV researcher said he was still recovering from a COVID infection that had left him unable to walk, put him in the hospital, and made him delusional, he said Wednesday during a roundtable discussion about long COVID.

Presented by the Global Virus Network, a coalition of leading virologists, the two-day virtual conference convened experts across disciplines and around the world to ask and answer questions about what causes long COVID, how to predict who gets it, how to treat it, and just possibly how to prevent it.

No one has the answers, but Gallo, who co-founded the group and is also Director of the Institute of Human Virology at the University of Maryland School of Medicine, puts his money on the amount of virus present right from the start. “We have definitive data that vaccine reduces virus, so if we can take that as a conclusion that the amount of virus is critical to predicting the future, you have a great biomarker,” he said. “I don’t think you can wait. I agree with those clinical people who want to go forward right away.”