How much virus does someone with COVID produce? A new study has an answer

The device, called Gesundheit-II, can collect viral RNA produced by people infected with SARS-CoV-2.Credit: Isabel Teresa Sierra Maldonado

People infected with the Alpha, Delta and Omicron variants of SARS-CoV-2 produce more virus than those infected with other variants, according to a new study.1. In addition, people infected with COVID-19 can spread the virus into the air after vaccination, even after a booster dose.

The work was published on the medRxiv preprint server on July 29. It has not yet been peer-reviewed.

“This study shows that all three variants that beat the infection race are more efficiently removed from the body when people talk or scream,” says John Volkens, a public health engineer at Colorado State University. University of Fort Collins.

According to Kristen Coleman, an author of the emerging infectious disease study at the University of Maryland in College Park, this means people “need to push governments to invest in improving indoor air quality by improving ventilation and filtration systems.”


For the study, Coleman and his colleagues recruited 93 people with SARS-CoV-2 between mid-2020 and early 2022. The participants’ infections were caused by strains including the Alpha variant that emerged in late 2020 and the later Delta and Omicron variants. All participants with the latter two strains were fully vaccinated before exposure to the virus.

Sick people faced the cone-shaped device and coughed, sneezed, sang and shouted for 30 minutes. The device, called Gesundheit-II, released tiny “aerosol” droplets 5 micrometers or less in diameter that could stay airborne and flow through cloth and surgical masks.

The team found that participants infected with the Alpha, Delta and Omicron variants released significantly more viral RNA in their breath than those infected with the other variants. These include ancestral variants such as Gamma, which was first discovered in Wuhan, China, and appeared in late 2020. For Delta and Omicron participants, their fine aerosols were five times higher on average. the size of the virus found in their larger, coarser aerosols.

The team also successfully infected cells in the laboratory with SARS-CoV-2 by inoculating them with one of four aerosol samples, each from a participant with Delta or Omicron. Shed virus is not always contagious, said study author Jianyu Lai, an epidemiologist at the University of Maryland, and the ability of samples to infect laboratory cells suggests that viral RNA in exhaled aerosols can spread the disease.

Malin Alsved, an aerosol technology scientist at Lund University in Sweden, says: “I’m worried that they’re going to mess up all the respiratory systems. [aerosols] — they have breathing, talking, talking, shouting, coughing, and even sneezing.” Coleman responds that the team’s respiratory systems have put together patterns to mimic a real-life scenario, such as being in a restaurant.

Going viral

The study also highlights variation in the amount of virus exhaled among individuals, ranging from undetectable levels to those associated with “superspreaders.” For example, one participant infected with Omicron shed viral RNA through a fine aerosol that was three times the highest level seen in individuals infected with Alpha or Delta. Researchers say the root of these discrepancies remains a mystery, but may be linked to biological factors such as a person’s age. Behavior may also play a role: The supersprayers in the study coughed more often than others.

If new variants are more likely to spread, this could make them more prevalent in cases of COVID-19. The team notes that people infected with SARS-CoV-2 produce less viral RNA than people with the flu. This suggests that SARS-CoV-2 can suppress even more virus-transmitting variants.

“It’s something to worry about,” says Alsved.

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