A group of scientists who remain convinced of the possibility of a lab leak wrote an open letter in early March when the W.H.O. team report was first anticipated demanding a thorough investigation of Chinese labs. Virologists who have studied the evolution of coronaviruses and the way they have jumped to humans in the past causing SARS and MERS continue to argue that the evidence for a natural origin apart from a lab leak is overwhelming.
The Chinese government, prominent Chinese scientists and many virologists, who study the evolution of viruses and the appearance of infectious diseases, have said the lab leak theory was very unlikely, citing genetic evidence and the many opportunities for natural infection in human interactions with animals like bats, where the virus is believed to have originated.
When Dr. Anthony S. Fauci, the United States’ top infectious disease expert, was asked at a White House news conference on the pandemic on Friday about Dr. Redfield’s comments, he noted that the remarks were only an opinion. Dr. Fauci said that there are different ways viruses could become adapted to humans.
“You know one of them is in the lab and one of them, which is the more likely, which most public health officials agree with, is that it likely was below the radar screen, spreading in the community in China for several weeks if not a month or more, which allowed it, when it first got recognized clinically to be pretty well adapted,” Dr. Fauci said.
At the same news conference on Friday, Dr. Rochelle Walensky, the current director of the C.D.C., said she was looking forward to reviewing the upcoming joint report from the W.H.O. experts and Chinese scientists.
“I don’t have any indication for or against either of the hypotheses that Dr. Fauci just outlined,” she said.
Zachary Montague and Isabella Grullón Paz contributed reporting.