Not only does the science not support this, but it’s also been clear for months that outdoor transmission risk for COVID-19 is nearly non-existent. However, the CDC has insisted on using an inflated number to stake out a “conservative” risk position that undermines policies that might promote public health. What happened? The New York Times’ David Leonhardt drills down into the data and finds an organization that appears lost in politics rather than on the leading edge of science:

It appears to be based partly on a misclassification of some Covid transmission that actually took place in enclosed spaces (as I explain below). An even bigger issue is the extreme caution of C.D.C. officials, who picked a benchmark — 10 percent — so high that nobody could reasonably dispute it.

That benchmark “seems to be a huge exaggeration,” as Dr. Muge Cevik, a virologist at the University of St. Andrews, said. In truth, the share of transmission that has occurred outdoors seems to be below 1 percent and may be below 0.1 percent, multiple epidemiologists told me. The rare outdoor transmission that has happened almost all seems to have involved crowded places or close conversation.

Saying that less than 10 percent of Covid transmission occurs outdoors is akin to saying that sharks attack fewer than 20,000 swimmers a year. (The actual worldwide number is around 150.) It’s both true and deceiving.

This isn’t just a gotcha math issue. It is an example of how the C.D.C. is struggling to communicate effectively, and leaving many people confused about what’s truly risky.

How did the CDC get a figure like 10%? Even with bad research, Leonhardt can’t quite figure it:

In one study, 95 of 10,926 worldwide instances of transmission are classified as outdoors; *all* 95 are from Singapore construction sites.

In another study, four of 103 instances are classified as outdoors; again, all four are from Singapore construction sites.

— David Leonhardt (@DLeonhardt) May 11, 2021

Even those didn’t add up to anything close to a 10% risk, however:

And yet even counting all the Singapore cases as outdoors still suggests only about 1% of transmission was outdoors.

Other studies — from Ireland and China — put the share at 0.1% or less.

— David Leonhardt (@DLeonhardt) May 11, 2021

This isn’t just a case of erring on the side of caution. Their benchmark is so disconnected to the reality of the underlying data, even from bad studies, that it’s clearly an arbitrary choice. And that has consequences; the CDC’s risk assessment drove policy decisions that led to shutdowns of outdoor venues, and in other cases mask requirements and social pressure that turned out to be entirely unnecessary. Even the rare outdoor transmission cases found in the studies almost all originated in lengthy and close exposure between people, not random and distanced exposure.

Put simply, the outdoors was, has been, and still is the best place for people to be in this pandemic. That’s especially true in sunny, warm-weather states. Rather than use legitimate risk assessment that might have allowed for people to make wiser choices for socializing, the CDC misled people into thinking that the risks were similar or at least in the same range as indoor transmission while masked and distanced. Not only did that make transmission more likely, the lack of outdoor exercise and fresh air may have made people less healthy overall and therefore more susceptible to disease.

This is yet another example of the CDC turning itself from a science-based agency to a social scold and political advocacy organization. Leonhardt makes clear that the 10% figure had no scientific basis, nor even had any research that put the risk at that level. People have lamented the lack of trust that Americans now have in experts, especially in this field, but that’s a mistrust that experts have earned through incompetence and flat-out dishonesty. And that will continue to have its toll on the lives and health of the nation.

Addendum: It leads to this conclusion:

Susan Collins says she used to always consider the CDC "the gold standard."

"I don't anymore," she says at hearing

— Manu Raju (@mkraju) May 11, 2021

Don’t blame the people for the CDC’s failures.