Vanishing Act

This deleted version of the CDC's website may actually be more accurate

For a brief moment last week, the CDC's website reflected the current scientific consensus on how Covid-19 spreads. Then it didn't.

More than two billion people have visited the Centers for Disease Control and Prevention's website during the coronavirus pandemic. With that number of eyes, it is no surprise that, on Friday last week, one of them noticed a sudden change to the site. The unannounced edit seemed to signal a huge shift in how the agency portrays the spread of coronavirus.

They were also bound to notice when it was hastily removed just three days later.

Editor's Note: On October 5, the CDC's website was updated to reflect that the coronavirus spreads through aerosols. The page now has a subheading that reads "Covid-19 can sometimes be spread through airborne transmission."

The update, shown below, specifies that the risk is far higher in certain environments, like indoor, poorly ventilated spaces with high concentrations of people.

The change is congruent with case studies that have prompted scientists to investigate transmission of Covid-19 through small aerosols. That includes the spread of the virus throughout restaurants, office buildings and choir practices.

The CDC's updated guidance on how the coronavirus spreads.

Still, the site emphasizes that it is "much more common" for the disease to spread through close contact.

On Friday, the CDC's website was apparently updated to suggest that the novel coronavirus may spread through respiratory droplets, or "small particles," including aerosols. The guidance pointed to growing evidence that these small droplets could "remain suspended in the air and be breathed in by others, and travel distances beyond 6 feet."

It was a radical change from the site's previous iteration, which suggested the biggest risks for coronavirus transmission came from respiratory droplets spread through close contact (within six feet). Instead, it reflected the latest science suggesting that the coronavirus can spread via smaller, aerosolized particles not encountered through direct contact with an infected person.

But by Monday, the change was gone. As a federal official familiar with the matter told CNN, the initial publication of the updated guidance (suggesting that aerosols do play a role in the spread of coronavirus) was a mistake.

The CDC's website also says that the update was an error.

"Somebody hit the button and shouldn't have," the official said.

The CDC's accidental change to the website, reflecting possibility of aerosolized spread of the virus. Captured on Saturday, September 19. It has since been removed.

CDC/Wayback Machine

The CDC's since-deleted draft is actually a better reflection of the current science of airborne transmission than the text now on the site. The seeming walk-back has reignited frustrations over inconsistent guidance from the agency, and the consequences for controlling the pandemic.

Was the change warranted? – The CDC's initial change reflects the findings of dozens of studies and updated guidance from the World Health Organization suggesting that the coronavirus may spread through small aerosols.

Smaller aerosols are typically less than about five microns in size (that's almost the size of a red blood cell). Unlike larger droplets, which can fall to the ground after about six feet of distance, these smaller droplets can stay suspended in the air, as studies this summer showed.

A video released in the New England Journal of Medicine showed that simply speaking could release thousands of droplets between 20 and 200 microns in size. In May, the same team published a follow-up study in the journal PNAS suggesting droplets between 10 and 20 micrometers can dehydrate, shrink, and fall to the ground slowly, lingering in the air for some eight to 14 minutes in a stagnant air environment.

Those studies suggest droplets are released while talking and can stay suspended. They didn't prove the coronavirus really does spread that way. But case studies have helped fill in the picture.

Take the April case study on a restaurant in Guangzhou, China. One asymptomatic diner infected five others who sat at two neighboring tables, even though they had no direct contact with the sick individual. Then, in May, came the now infamous choir case study from Skagit County, Washington. During a 2.5 hour indoor choir practice, 53 out of the 61 choir members became ill. The act of singing may have contributed to spread through "emission of aerosols," the CDC report on the event read.

On July 6, 239 scientists co-signed a letter to the World Health Organization urging the organization to recognize risks of aerosols – especially in indoor, poorly ventilated spaces. On July 9, the organization issued an updated guidance, and acknowledged that in crowded, poorly ventilated spaces, aerosolized transmission "couldn't be ruled out."

The CDC's website had never reflected that change in thinking until the draft guidance appeared on Friday. But then it was swiftly removed.

The dangers of a flip-flop – The change to the CDC website is just the latest in a series of flip-flops. Under political pressure, the CDC changed the testing guidelines to advise people exposed to the virus but who were not symptomatic did not "necessarily" need a Covid-19 test.

After public outcry, that decision was reversed.

Left: the CDC with the updated guidance. Right: the CDC's website after the updated guidance was removed Monday.


The most notorious change in stance is the CDC's attitude towards masks and face coverings, which were not recommended by the agency as late as April. Rather, the agency suggested that masks needed to be reserved for healthcare workers facing severe shortages. Now, masks are thought to be one of the most powerful tools for controlling the virus.

The radical change had consequences. As Anthony Fauci, director of the Institute of Allergy and Infectious Diseases told All Things Considered: "We have to admit it, that that mixed message in the beginning, even though it was well meant to allow masks to be available for health workers, that was detrimental in getting the message across."

Transparency and willingness to reevaluate should inspire confidence, as Catherine Clase, associate professor of medicine at McMaster University, told Inverse previously. It doesn't always work out that way –as the continued contentiousness around masks demonstrates. Instead of inspiring confidence, the seeming u-turn on masks made people "feel that the decision was not as clear cut," Clase said.

Change in itself isn't a reason for mistrust – especially if it's based on updated understanding of the science. We've seen the science of aerosols progress over the summer, slowly revealing how risky they really are.

The draft statement, had it remained, might have been a change for the better. As Donald Milton, one of the 239 scientists who wrote to the WHO and an environmental health professor at the University of Maryland told CNN: "I think that the science behind what turned out to be a draft statement is strong and agrees with my understanding of the data."

Instead, the removal of that draft statement appears to be another pivot by the agency — but this time, away from the science.

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