Inhalation of contaminated aerosol is the primary mode of transmission of the coronavirus. Scientists at the University of Maryland (USA) investigated how infectious the aerosol that patients with various strains of coronavirus exhale when they exhale. The study included 93 patients with COVID-19. Most participants have mild symptoms. All participants infected with the Delta and Omicron strains were fully vaccinated / boosterized against coronavirus before infection and had IgG antibodies.
The study found that people infected with the highly contagious strains of coronavirus Alpha, Delta and Omicron shed more virus than those infected with other strains, regardless of vaccination and the presence of antibodies. The virus is shed most strongly when people speak or shout.
To determine the amount of virus shed, the scientists used a cone-shaped apparatus into which patients sang and screamed, sneezed and coughed for 30 minutes. The device collected viral samples and separated tiny aerosol droplets with a diameter of up to 5 micrometers, which can linger in the air and seep through the surgical mask. Delta and Omicron participants’ exhaled fine aerosols (≤ 5 µm) contained 100 times more virus than larger aerosols.
At the next stage of the study, the scientists showed that the collected aerosol with the Delta and Omicron strains infects lung epithelial cells expressing TMPRSS2 and ACE2, the proteins the coronavirus uses to enter the cell. The viral RNA found in the exhaled aerosol can spread the coronavirus.
During the cone-shaped apparatus experiment, the scientists collected all types of aerosol at once – from breathing, talking, screaming, sneezing and coughing, simulating a real scenario, such as being in a restaurant.
The amount of virus exhaled ranged from undetectable to excessively high levels, significantly increasing the likelihood of infection. One of the patients infected with the Omicron strain excreted 1,000 times more viral RNA in exhaled aerosol than other patients infected with the Alpha and Delta strains. Perhaps this difference is due to age or the fact that the patient coughed more often, and patients with Delta and Omicron cough more often.
If a patient sheds excessively high levels of viral RNA when infected with a new strain of coronavirus, this can cause the new strain to overspread and become dominant.
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References
- Evolution of SARS-CoV-2 Shedding in Exhaled Breath Aerosols
- How much virus does a person with COVID exhale? New research has answers
