The CDC’s Updated Guidance On Airborne & Asymptomatic Spread Of COVID-19 – Redux

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Note: The above retraction by the CDC was posted Sept 21st – 3 days after the new guidance was posted. 

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Two weeks ago, in The CDC’s Updated Guidance On Airborne & Asymptomatic Spread Of COVID-19we looked at recently posted changes to the CDC’s COVID-19 guidance on COVID-19 transmission that placed more emphasis on the potential for airborne spread. 

While welcomed, the CDC’s acknowledgement that COVID-19 can spread via aerosols and by asymptomatic cases was more of an incremental change than a seismic shift. In July 200+ scientists from around the world signed an open letter to the WHO, urging them to reconsider their stance on the airborne spread of the virus.

Hours after I posted that blog, that new guidance disappeared and the (above) retraction was posted on the CDC site. 

Although I can’t promise today’s changes won’t be reversed again, the CDC has posted a new update (dated today, Oct 5th) that incorporates much of what was published – and then retracted – 2 weeks ago. After which you’ll find a link to a more detailed scientific brief from the CDC. 

How COVID-19 Spreads
Updated Oct. 5, 2020
 

COVID-19 is thought to spread mainly through close contact from person to person, including between people who are physically near each other (within about 6 feet). People who are infected but do not show symptoms can also spread the virus to others. We are still learning about how the virus spreads and the severity of illness it causes.

 

COVID-19 spreads very easily from person to person

How easily a virus spreads from person to person can vary. The virus that causes COVID-19 appears to spread more efficiently than influenza but not as efficiently as measles, which is among the most contagious viruses known to affect people.
  • COVID-19 most commonly spreads during close contact
  • People who are physically near (within 6 feet) a person with COVID-19 or have direct contact with that person are at greatest risk of infection.
  • When people with COVID-19 cough, sneeze, sing, talk, or breathe they produce respiratory droplets. These droplets can range in size from larger droplets (some of which are visible) to smaller droplets. Small droplets can also form particles when they dry very quickly in the airstream.
  • Infections occur mainly through exposure to respiratory droplets when a person is in close contact with someone who has COVID-19.
  • Respiratory droplets cause infection when they are inhaled or deposited on mucous membranes, such as those that line the inside of the nose and mouth.
  • As the respiratory droplets travel further from the person with COVID-19, the concentration of these droplets decreases. Larger droplets fall out of the air due to gravity. Smaller droplets and particles spread apart in the air.
  • With passing time, the amount of infectious virus in respiratory droplets also decreases.

COVID-19 can sometimes be spread by airborne transmission
  • Some infections can be spread by exposure to virus in small droplets and particles that can linger in the air for minutes to hours. These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space.
  • This kind of spread is referred to as airborne transmission and is an important way that infections like tuberculosis, measles, and chicken pox are spread.
  • There is evidence that under certain conditions, people with COVID-19 seem to have infected others who were more than 6 feet away. These transmissions occurred within enclosed spaces that had inadequate ventilation. Sometimes the infected person was breathing heavily, for example while singing or exercising.
    • Under these circumstances, scientists believe that the amount of infectious smaller droplet and particles produced by the people with COVID-19 became concentrated enough to spread the virus to other people. The people who were infected were in the same space during the same time or shortly after the person with COVID-19 had left.
  • Available data indicate that it is much more common for the virus that causes COVID-19 to spread through close contact with a person who has COVID-19 than through airborne transmission. [1] 
COVID-19 spreads less commonly through contact with contaminated surfaces 
  • Respiratory droplets can also land on surfaces and objects. It is possible that a person could get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or eyes.
  • Spread from touching surfaces is not thought to be a common way that COVID-19 spreads
COVID-19 rarely spreads between people and animals
  1. It appears that the virus that causes COVID-19 can spread from people to animals in some situations. CDC is aware of a small number of pets worldwide, including cats and dogs, reported to be infected with the virus that causes COVID-19, mostly after close contact with people with COVID-19. Learn what you should do if you have pets.
  2. At this time, the risk of COVID-19 spreading from animals to people is considered to be low. Learn about COVID-19 and pets and other animals.
Protect yourself and others

The best way to prevent illness is to avoid being exposed to this virus. You can take steps to slow the spread.

Pandemics can be stressful, especially when you are staying away from others. During this time, it’s important to maintain social connections and care for your mental health.

Learn more about what you can do to protect yourself and others.
1Pathogens that are spread easily through airborne transmission require the use of special engineering controls to prevent infections. Control practices, including recommendations for patient placement and personal protective equipment for health care personnel in healthcare settings, can be found in Section 2 of Interim Infection Prevention and Control Recommendations for Healthcare Personnel During the COVID-19 Pandemic.

Scientific Brief: SARS-CoV-2 and Potential Airborne Transmission
Updated Oct. 5, 2020