COVID-19 Resource Center

COVID-19 Resource Center

September 21, 2020
2 min read

CDC adds, then removes mention of airborne spread of SARS-CoV-2 on website

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The CDC added and then removed a note on its website that said SARS-CoV-2 is commonly spread via airborne transmission, saying that the update was part of new guidance that is still under review and was posted by mistake.

The update, posted Friday on a page titled “How COVID-19 Spreads,” said SARS-CoV-2 most commonly spreads via close contact with people and “through respiratory droplets or small particles, such as those in aerosols, produced when an infected person coughs, sneezes, sings, talks or breaths.”

Amesh A. Adalja


“These particles can be inhaled into the nose, mouth, airways, and the lungs and cause infection This is thought to be the main way the virus spreads,” the updated language read.

Previously — and now again — the page made no mention of aerosols. The CDC page says the virus mainly spreads in close contact via respiratory droplets from coughing, sneezing or talking.

“A draft version of proposed changes to these recommendations was posted in error to the agency’s official website,” the CDC said in a statement posted to the webpage. “CDC is currently updating its recommendations regarding airborne transmission of SARS-CoV-2 (the virus that causes COVID-19). Once this process has been completed, the update language will be posted.”

The potential for airborne transmission of SARS-CoV-2 has been a topic of debate. Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said previously that a “reasonable assumption” can be made that airborne transmission may occur.

“Aerobiology studies show that airborne viral particles can be isolated. However, it is important to remember that aerobiology studies do not substitute for epidemiology, and epidemiologically speaking we are not seeing a measles-like transmission with this virus — especially in households,” Amesh A. Adalja, MD, senior scholar at Johns Hopkins Center for Health Security, told Healio.

“There is a bit of a semantic issue over aerosol and droplet transmission in that there is a difference between the way aerobiologists speak about it and the way infectious disease doctors, who are attuned to hospital infection control measures, speak of it,” Adalja said.

Mike Ryan, MD, MPH, executive director of WHO’s health emergency program, said in a press conference that WHO was “in touch” with CDC to clarify the issue.

“We have not seen any new evidence, and our position on [airborne transmission] remains the same,” Ryan said. “We have always said, going back over months and months, that there is potential for different kinds of routes of transmission — particularly driven by the context, the proximity, the intensity, duration and the potential for different forms of transmission, including small particle transmission in poorly ventilated spaces and the need for the appropriate precautions.”

Maria Van Kerkhove, PhD, WHO’s COVID-19 technical lead, said people should continue to manage their risk by using masks, avoiding closed, crowded settings, ensuring good ventilation and maintaining proper hand hygiene and respiratory etiquette.

“From the beginning, transmission and severity are two of the main features of any new pathogen that are really critical to better understand,” Van Kerkhove said. “We are always looking at the literature. What really matters is how we protect people, and how we ensure that transmission is reduced and suppressed.”

A WHO scientific briefing noted that airborne transmission of the coronavirus can happen during aerosol-generating medical procedures, particularly in indoor settings with subpar ventilation.

Adalja also noted that ventilation plays a role in the potential for airborne transmission.

“We know that outdoor transmission is less likely than indoor transmission, and it’s important to try and develop ways to increase ventilation to mimic the outdoors as best as possible,” he said.


CDC. How COVID-19 spreads. Accessed September 21, 2020.

WHO. Transmission of SARS-CoV-2: implications for infection prevention precautions. Accessed September 21, 2020.