This morning, I am going to tell you another story about the C.D.C. and its approach to Covid-19 behavioral guidelines. It’s a story that highlights the costs of extreme caution.
When Dr. Rochelle Walensky, the C.D.C. director, appeared before a Senate committee this month and defended the agency’s description of how often Covid-19 is transmitted outdoors, she cited a single academic study.
She was responding to a question from Senator Susan Collins of Maine, who had asked why some C.D.C. guidelines seemed inconsistent with the available data. Collins quoted from that day’s edition of this newsletter and argued that the C.D.C. was exaggerating the risk of outdoor activities by claiming that “less than 10 percent” of Covid transmission occurred outside.
Anything close to 10 percent would mean that outdoor infections were a huge problem. Yet the true share appears to be closer to 0.1 percent.
a study published in The Journal of Infectious Diseases. The study was “a meta-analysis,” she explained, which means it synthesized data from other studies. “The topline result of all studies that were included in the systematic review said less than 10 percent of cases were transmitted outdoors,” she said.
Her answer made the study sound definitive. Walensky did not mention any other studies or offer any logical argument for why she believed outdoor transmission was a significant risk. She implied that the C.D.C. was simply listening to The Journal of Infectious Diseases, which, as she noted, is a top journal.
Later that day, one of the study’s authors posted several messages on Twitter, and the story got more complicated.
‘An amazing resource’
The tweets came from Dr. Nooshin Razani, an epidemiologist at the University of California, San Francisco. In them, she emphasized that the study’s results suggested that the share of Covid occurring outdoors was “much lower than 10 percent.” The central message of the paper, Razani wrote, was the relative safety of the outdoors:
in her testimony, had used the two terms interchangeably.)