The number of coronavirus cases and deaths isn’t the only thing changing on a daily basis; so is our understanding of the behavior of the coronavirus and its transmission.
After believing for months that the coronavirus spreads predominantly through direct contact with large respiratory droplets, the World Health Organization (WHO) recently adjusted its standpoint. However, the WHO’s stance didn’t change randomly: it occurred soon after 239 scientists from more than 30 countries signed a letter asking the WHO to consider the serious potential of airborne COVID-19 transmission.
The Science of Aerosol Transmission
A growing body of evidence suggests that SARS-CoV-2, the coronavirus responsible for the COVID-19 pandemic, can spread through more than a sneeze or cough. According to aerosol scientists Lidia Morawska and Donald Milton, the virus can pass from person to person in tiny droplets called aerosols.
These aerosols, just like the aerosols created by hairspray and other common household products, waft through the air and accumulate over time. Scientists like Morawska and Milton say studies have demonstrated “beyond any reasonable doubt” that viruses are released when people exhale and talk. Those microdroplets are so small that they can remain in the air and pose a risk of exposure to others, even from a “safe” social distance.
A study published in May sought to better understand the behavior of aerosols and microdroplets. Study researchers used laser-light scattering to detect droplets emitted by healthy volunteers when speaking. The authors found that for SARS-CoV-2, one minute of loud speaking generates upwards of 1,000 small, virus-laden aerosols that linger in the air for at least 8 minutes.
Based on these findings, the study concluded that “there is a substantial probability that normal speaking causes airborne virus transmission in confined environments.”
WHO Confirms the Possibility of Airborne Transmission
The WHO responded to Morawksa, Milton, and their scientific community shortly after their open letter was published.
“We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of COVID-19,” Maria Van Kerkhove, technical lead on the COVID-19 pandemic at the WHO, explained in a news briefing.
However, the WHO is not ready to definitively confirm the role of airborne transmission in the coronavirus pandemic. Benedetta Allegranzi, the WHO’s technical lead for infection prevention and control, elaborated on this during a news briefing in Geneva on July 7.
“We have to be open to this evidence and understand its implications regarding the modes of transmission, and also regarding the precautions that need to be taken.”
As Cities Reopen, What Needs to Change?
In light of the possibility for aerosols to spread the virus, governors across the U.S are implementing COVID-19 precautions that go beyond social distancing and sanitation.
Morawska and Milton recommend the following additional measures to maximize safety and limit the growing number of coronavirus cases in the U.S:
- Provide sufficient and effective ventilation in public buildings, workplace environments, schools, hospitals, and nursing homes
- Supplement general ventilation with airborne infection controls such as local exhaust, high efficiency air filtration, and germicidal UV lights
- Avoid overcrowding in public transportation and buildings
- Wear masks in all public and enclosed spaces
As the authors emphasize, working with the WHO to establish the true methods of COVID-19 transmission is now officially of “heightened significance.”