Lancet published an article1) on May 1. 2021 “10 scientific reasons in support of airborne transmission of SARS-CoV-2”. We introduce the article piece by piece with a solution how to successfully avoid, remove and destroy viruses from indoor air.
1. Superspreading events
Superspreading events account for substantial SARS-CoV-2 transmission; indeed, such events may be the pandemic’s primary drivers.1)
Viruses are transmitted through aerosols at several meter distances, especially indoors when people gather in events. There are many sad examples of group transmissions in indoor events, such as private parties and concerts, like the one held in the Helsinki Music Centre to celebrate the International Women's day in March 2020).
2. Long distance transmission through air channels
Long-range transmission of SARS-CoV-2 between people in adjacent rooms but never in each other's presence has been documented in quarantine hotels.1)
SARS-CoV-2 travels long distance in ventilation channels and stays contagious during hours. Therefore it is important to decontaminate the air flowing through the ventilation channels.
3. Trasmission without coughing or sneezing
Asymptomatic or presymptomatic transmission of SARS-CoV-2 from people who are not coughing or sneezing is likely to account for at least a third, and perhaps up to 59%, of all transmission globally.1)
"The incubation period is the time from infection to the beginning of the first symptoms. The incubation period of the disease is estimated to be 1–14 days, the most common symptoms appearing about 4–5 days after infection.According to current knowledge, a person with coronavirus disease is most contagious at the beginning of a symptomatic disease and just before the onset of symptoms. The infected person can spread the virus 1 to 2 days before the onset of symptoms. An asymptomatic person may also be a source of infection. However, according to the WHO, the majority of infections are caused by symptomatic individuals." Source: THL3)
4. Transmission risk biggest indoors
Transmission of SARS-CoV-2 is higher indoors than outdoors and is substantially reduced by indoor ventilation.1)
The best ways to reduce the indoor transmission of SARS-CoV-2 is through window ventilation and by making sure the room has at least 2 air changes per hour. Although the transmission risk is great indoors, it can be remarkably reduced by turning up the ventilation, opening the windows and using air purifiers along with longer safety distances and adequate masks. Source: Helsingin Sanomat2)
5. Protective equipment against droplet exposure are inefficient
Infections have been documented in health-care organizations, where personal protective equipment is designed to protect against droplet but not aerosol exposure.1)
“More advanced masks and other protective equipment are required in potentially virus-rich indoor environments including medical centers and hospitals. Masks are particularly effective in combination with other preventive measures like ventilation and distancing.”4)
6. SARS-CoV-2 can stay infectious in the air for hours
Viable SARS-CoV-2 has been detected in the air. In laboratory experiments, SARS-CoV-2 stayed infectious in the air for up to 3 h with a half-life of 1h.
A 1 micron spherical aerosol particle with the density of water would take 7,5 hrs to sink to the ground from a height of 1 meter. A 10 micron particle would need only 6 minutes and a 0,4 micron particle 39 hours.5)
7. Found in locations only reachable by aerosols
SARS-CoV-2 has been identified in air filters and building ducts in hospitals with COVID-19 patients; such locations could be reached only by aerosols.1)
Optimally Healthcare facilities should be equipped with an electronic filtering system, making it possible to filter the most harmful particles – viruses, bacteria, pollen, dust from the street, air pollutants and vehicle emissions, etc. – out of the incoming air.
8. Transmissions between caged animals
Studies involving infected caged animals that were connected to separately caged uninfected animals via an air duct have shown transmission of SARS-CoV-2 that can be adequately explained only by aerosols.1)
It has long been known that SARS-CoV-2 pathogens are spread mainly through aerosol particles. Aerosol, a combination of air and liquid ingredients, is formed in the lungs and released into the room when inhaled and spoken. Aerosols hover for several hours in the air in the room, so that other people can breathe them as infectious particles.
9. No evidence against airborne SARS-CoV-2 transmission
No study to our knowledge has provided strong or consistent evidence to refute the hypothesis of airborne SARS-CoV-2 transmission. Some people have avoided SARS-CoV-2 infection when they have shared air with infected people, but this situation could be explained by a combination of factors, including variation in the amount of viral shedding between infectious individuals by several orders of magnitude and different environmental (especially ventilation) conditions.1)
As we have learned that the risk of contracting the virus from touching a contaminated surface is close to non-existent.6) The results of studies suggest that the chance of getting SARS-CoV-2 infection from contaminated surface is less than 1 in 10,000. According to the C.D.C., the other transmission routes are more remarkable: droplet transmission, airborne transmission and direct contact.7)
The experts state that organizations around the world have been spending massive amounts of time and money to deep-clean surfaces, while other transmission routes have been a remarkably bigger problem. According to them, we should shift our effort toward cleaning shared air, not shared surfaces.8)
10. Limited evidence to support other dominant transmission routes
There is limited evidence to support other dominant routes of transmission—ie, respiratory droplet or fomite. Ease of infection between people in close proximity to each other has been cited as proof of respiratory droplet transmission of SARS-CoV-2. However, close-proximity transmission in most cases along with distant infection for a few when sharing air is more likely to be explained by dilution of exhaled aerosols with distance from an infected person.1)
As people want to meet and interact, taking care of proper air hygiene is very important. Using an air purifier can be seen as increasing the ventilation. There is a rule of thumb: if an air purifier doubles the volume of ventilation, the aerosol content approximately halves.9)
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Sources:
1) https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00869-2/fulltext
2) https://www.hs.fi/kotimaa/art-2000007842978.html
4) https://science.sciencemag.org/content/early/2021/05/19/science.abg6296
5) https://www.info.gaef.de/positionspapier
6) https://www.genano.com/infobase/statistics-show-the-risk-of-catching-the-coronavirus-from-surfaces-is-low
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