CDC Revises Covid-19 Guidance, Acknowledges Aerosols, Then Changes Their Mind

Many scientists, engineers and architects were excited after the Center for Disease Control revised its recommendations on September 18 to acknowledge the importance of aerosol transmission, something that we have been discussing on Treehugger since March. Finally, after all this time, hundreds of professionals, CDC and the WHO, the ventilation experts were all talking on the same page.

"It is possible that COVID-19 may spread through the droplets and airborne particles that are formed when a person who has COVID-19 coughs, sneezes, sings, talks, or breathes. There is growing evidence that droplets and airborne particles can remain suspended in the air and be breathed in by others, and travel distances beyond 6 feet (for example, during choir practice, in restaurants, or in fitness classes). In general, indoor environments without good ventilation increase this risk.... In general, the more closely a person with COVID-19 interacts with others and the longer that interaction, the higher the risk of COVID-19 spread."

The really big deal in the change is that previously the guidance was all about staying six feet apart because the droplets were supposed to be big and fall quickly, whether you were inside or out; the new guidance indicated that the distance is less relevant, the ventilation more so.

This tweet shows how big a deal this was in the community. It really changed everything, raising questions about the approach to dealing coronavirus. And then:

On the morning of September 21, the page was pulled by the CDC and a notice put up in its place. Nobody is sure why; according to the Washington Post, it was all a mistake.

Jay Butler, the CDC’s deputy director for infectious disease, said the Friday update was posted in error. “Unfortunately an early draft of a revision went up without any technical review,” he said. The edited web page has removed all references to airborne spread, except for a disclaimer that recommendations based on this mode of transmission are under review. “We are returning to the earlier version and revisiting that process," Butler said. "It was a failure of process at CDC.”

Others are not so sure that it was just an error; from the Post:

Experts who reviewed CDC’s Friday post had said the language change had the power to shift policy and public behavior. Some suggested it should drive a major rethink of public policy — particularly at a time when students in many areas are returning to indoor classrooms.

Indeed, I had just written a post about the change prior to the retractions, stating:

What does this all mean?

"Basically, you do not want to go to a Trump rally, or any other crowded, poorly ventilated indoor space where people don't wear masks. This also doesn't bode well for the restaurant industry, where people are close together, talking, and not wearing masks. It also raises many questions about kids returning to school, as the experts who have been calling for the change in policy noted in their FAQ:

"Unfortunately schools typically fulfill many the requirements for efficient virus transmission: indoors, crowding, low ventilation, close proximity, long duration, unmasked, talking/singing/yelling/breathing hard. Ventilation rates are often low. There is a lot of debate about how well children transmit the disease, with some evidence that younger children transmit it less well, and older children transmit it as well as adults. But schools, if not modified, are also the perfect situation to transmit it, which may make up for lower inherent transmissibility."

The changed CDC policy might have made people reconsider sending their kids to school or going back to the office, given that the six-foot rule was being called into question.

 Treehugger has been quoting the building science experts since March about how "the virus can remain viable floating in the air for some number of hours" and since April, that it could be spread through ventilation systems. In May we wrote about recommendations that "all possible precautions against airborne transmission in indoor scenarios should be taken." In July we quoted 239 researchers who wrote: "We appeal to the medical community and to the relevant national and international bodies to recognize the potential for airborne spread of COVID-19."

For a moment it looked like there was finally a consensus among the building scientists, the CDC and the WHO, it seemed that everyone was finally on board with aerosols. Now everyone is wondering just what happened.

If you want a complete and thorough expert analysis of the issue of aerosols, see: FAQs on Protecting Yourself from COVID-19 Aerosol Transmission.

https://docs.google.com/document/d/1fB5pysccOHvxphpTmCG_TGdytavMmc1cUumn8m0pwzo/edit#

https://www.treehugger.com/cdc-revises-covid-19-guidance-acknowledges-aerosols-then-changes-their-mind-5078755