In early July 2020, news reports discussed a seeming difference of opinion between scientists and the World Health Organization (WHO). At its core the difference related to whether or not SARS-CoV-2 can spread through aerosolized droplets, and it wasn’t so much a “rift” as it was the process of scientific discourse. But, given the pandemic and lack of tools to control it, the discourse resulted in pressure that led more than 200 scientists to support an open letter stating that there was enough evidence of aerosolized spread that the WHO should be including it in communications about COVID-19 transmission. The scientists convinced the WHO to make this update, but the discussion may have created questions and left some of your patients wondering what we know about transmission of SARS-CoV-2 at this point?

Routes of transmission

Almost since its inception, COVID-19 has been characterized as most commonly spreading in manners similar to other respiratory infections — through large respiratory droplets and contact with infected surfaces followed by touching one’s face. Coughing, sneezing, and even talking or singing can cause droplets containing infectious virus particles to spread to others or contaminate surfaces.

However, as described in the open letter, evidence also suggests small droplet spread. In terms of infection control, the difference between large and small droplet transmission is critical. Small droplets, defined as 5 microns or smaller, mean that the virus can spread through the air. As a result, decreasing transmission relies more heavily on ventilation and isolation, particularly because these droplets can travel longer distances and may hang in the air after an infected person has left.

Whereas large droplets are unlikely to travel more than 3 to 6 feet, small droplets can travel more than 10 to 13 feet. In practical terms, this means that people in the same room could be infected even without directly interacting. When considering how to stem transmission of COVID-19, this type of spread has implications for reopening places like restaurants and schools, where groups of people gather in small spaces. This was one of the reasons that the scientists felt the open letter was timely.

Takeaways for talking with patients:

  • Masking reduces spread from an infected person by decreasing chance for viral particles to spread to others or to contaminate surfaces.
  • Washing hands and not touching one’s face reduces the chance of getting infected.
  • Social distancing also reduces the chance of getting infected. While 6 feet is recommended, further distances may be better given the chance for small-droplet spread.
  • Indoor spaces with reduced or limited ventilation increase the chance for spread.

Who can transmit virus and when

One of the underlying themes of transmission is the idea that people who don’t have symptoms can spread COVID-19. While it remains unclear whether asymptomatic individuals can transmit the virus, it is clear that people who experience symptoms can spread the virus beginning about two days before symptoms start. And, people can spread virus throughout the period during which they are symptomatic. Symptoms typically occur within two days to two weeks of exposure, but it has varied in studies from different regions.

Takeaways for talking with patients:

  • Even people who are not experiencing symptoms can spread the virus, particularly if they develop symptoms within a day or two of contact.
  • It is not clear whether asymptomatic people can spread the virus. So, to be on the safe side, others should assume any infected individual could spread the virus, regardless of whether or not they have symptoms.

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.