The Epinhood (TEH)

CORONAVIRUS DISEASE 2019 UPDATE (07): AIRBORNE TRANSMISSION CONFIRMED

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A ProMED-mail post
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International Society for Infectious Diseases
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Date: Thu 10 Apr 2025
Source: CIDRAP (Center for Infectious Disease Research & Policy)
[edited] https://www.cidrap.umn.edu/covid-19/using-study-design-past-researchers-again-show-covid-19-airborne

In 1959, researchers built a facility near Pretoria, South Africa, to
study the airborne route of tuberculosis transmission, replicating an
experiment first done in Baltimore. With a detailed schematic of ward
rooms, test and control chambers, and room exhaust fans, the
researchers proved nature’s deadliest bacterium traveled through the
air, meaning infectious people in one part of a building could infect
others through a ventilation system.

Now researchers, led by Chad Roy, PhD, MSPH, from Tulane University,
have used the South African Airborne Infections Research (AIR)
facility to illustrate human-to-animal transmission of SARS-CoV-2, the
virus that causes COVID-19, through a building’s ventilation system.
The study was published last week [1 Apr 2025] in Open Forum
Infectious Diseases. “This was the first time the facility was used to
test virus transmission,” Roy told CIDRAP News. “And the study
continues to reveal things about the virus.”

Five years after the COVID pandemic began, it is widely accepted that
airborne transmission fuels the spread of the novel coronavirus. But
Roy said the study helps understand the virus dynamics at play, and
shows the virus is hardier than other viruses. “We had evidence of
long distance COVID transmission early on in the pandemic, like the
choral event in Washington state,” Roy said, referring to a March 2020
choir practice that resulted in up to 87% of participants infected
with COVID-19.

But for months in 2020 and into 2021 — until the omicron strain
emerged — experts debated how the virus was spread, at what distance
the virus was still transmissible, and how much physical distancing
was required to keep people safe. “We were really using ideas from
other viruses when looking at COVID,” said Roy.

In the new study, Roy and his colleagues used hamsters and newly
diagnosed COVID-19 patients to test airborne transmission. Seven
COVID-positive patients spent a cumulative 409.5 hours in the AIR
facility in the last 2 weeks of November 2022, while 216 hamsters were
exposed continuously to approximately 5% of the total ward ventilatory
exhaust. Four of the 7 patients were infected with the omicron strain,
1 with delta, and 2 had unknown sequencing. Two of the patients also
had HIV.

The hamsters were euthanized after 21 days in the exhaust path plus an
additional 7 days housing, and blood was collected for further
analysis. The authors found evidence of SARS-CoV-2 antibodies in 58%
of the hamsters, though none of the animals showed signs of
infection.

“The simplest interpretation of our results is that human-generated
aerosols seroconverted 58% of exposed hamsters after traveling the
7-10 meter distance through the ventilation system of the AIR
facility,” the authors wrote. “This data indicates that exposure to
exhaust air from the clinical ward containing individuals actively
infectious for SARS-CoV-2 can result in transmission to susceptible
animals.”

Lisa Brosseau, ScD, CIH, an expert on respiratory protection, said the
study adds to a growing body of literature showing SARS-CoV-2 can be
transmitted through the air. She said early debates about how and if
COVID could be transmitted through the air existed because the virus
behaves so differently than others.

“Unlike bacteria, which have a cell wall to protect them, viruses are
just strands of RNA and are usually not this hardy,” she said. “The
coronavirus evolved to stay alive in the air for quite a long time.”
The animals were not tested for SARS-CoV-2 status before the
experiment began, because Roy said exposing the animals to humans
before the study was too risky during the high-transmissibility of the
omicron period.

Both Roy and Brosseau, a research consultant with the University of
Minnesota’s Center for Infectious Disease Research and Policy
(CIDRAP), publisher of CIDRAP News, said it was highly unlikely the
animals could have had SARS-CoV-2 antibodies before the study.

CIDRAP Director Michael T. Osterholm, PhD, MPH, said this study was
beautifully designed. “This one was a classic study design, and we
don’t often say that in science,” said Osterholm. “This study should
put the nail in the coffin that SARS-CoV-2 is not transmitted by
airborne routes.”

[Byline: Stephanie Soucheray]