A device called the Gesundheit-II can collect viral RNA exhaled by people infected with SARS-CoV-2.Credit: Isabel Teresa Sierra Maldonado
According to one study1, people infected with the highly transmissible alpha, delta, and Omicron variants of SARS-CoV-2 shed higher amounts of virus than people infected with other variants. Also, people who get COVID-19 after vaccination, and even after a booster dose, continue to shed the virus through the air.
The work was published on the medRxiv preprint server on July 29. It has not yet been peer reviewed.
“This research showed that the three variants that won the infection race … leave the body more efficiently when people talk or shout than the first strains of the coronavirus,” says John Volckens, a public health engineer at Colorado State. University of Fort Collins.
Study co-author Kristen Coleman, who researches emerging infectious diseases at the University of Maryland in College Park, says this means people should “push governments to invest in improving indoor air quality by improving ventilation systems.” and filtration”.
Exhale
For the study, Coleman and colleagues recruited 93 people between mid-2020 and early 2022 who were infected with SARS-CoV-2. The participants’ infections were caused by strains including the Alpha variant, which emerged in late 2020, and later Delta and Omicron variants. All participants with the latter two strains had been fully vaccinated before contracting the virus.
Infected people faced a cone-shaped apparatus and sang and shouted, with inevitable coughs and sneezes in between, for 30 minutes, while an attached machine collected the particles they exhaled. The device, called the Gesundheit-II, separated fine ‘aerosol’ droplets measuring 5 micrometers or less in diameter, which can linger in the air and seep through cloth and surgical masks.
The team found that participants infected with the Alpha, Delta and Omicron variants emitted significantly more viral RNA when exhaling than people infected with other variants. These include ancestral variants, such as the one first detected in Wuhan, China, and those not associated with increased transmissibility, such as Gamma, which emerged in late 2020. For the Delta and Omicron participants, their fine spray contained on average five times the amount of virus that was detected in its largest and thickest aerosol.
The team also seeded cells in the lab with aerosol samples and found that four samples, each from a participant with Delta or Omicron, infected the cells. Shed virus isn’t always infectious, says study co-author Jianyu Lai, an epidemiologist at the University of Maryland, and the ability of samples to infect lab cells means viral RNA in exhaled aerosols can spread disease.
Malin Alsved, an aerosol technology scientist at Lund University in Sweden, says: “I’m a little concerned that they mix up all the airways. [aerosols] — they have breathing, talking, speaking, screaming, coughing and even sneezing in the sample”. Coleman counters that the team combined respiratory samples to mimic a real-life setting, such as being in a restaurant.
go viral
The study also highlights inter-individual variation in the amounts of virus exhaled, ranging from undetectable levels to those associated with “super-spreaders.” One participant infected with Omicron, for example, shed 1,000 times more viral RNA through a fine spray than the maximum level seen in those with Alpha or Delta. The researchers say the root of these discrepancies remains a mystery, but could be related to biological factors such as a person’s age. Behavior could also play a role: The study’s superspreader coughed more often than others.
If the new variants are more prone to superspreading, that could lead them to dominate COVID-19 cases. The team notes that people infected with SARS-CoV-2 exhale much lower amounts of viral RNA than people infected with influenza, a similar airborne illness. This suggests that SARS-CoV-2 could generate variants that transmit even more viruses.
“That’s something to worry about,” says Alsved.
Source: www.nature.com