‘Strong evidence’ COVID-19 predominantly spreads through air, says Lancet study

‘Transmission rates of SARS-CoV-2 are much higher indoors than outdoors’

NEW DELHI: There is consistent, strong evidence to prove that the SARS-CoV-2 virus, behind the COVID-19 pandemic, is predominantly transmitted through the air, according to a new assessment published on Friday in The Lancet journal.

The analysis by six experts from the UK, the US and Canada says public health measures that fail to treat the virus as predominantly airborne leave people unprotected and allow the virus to spread.

“The evidence supporting airborne transmission is overwhelming, and evidence supporting large droplet transmission is almost non-existent,” said Jose

Luis Jimenez, from the University of Colorado Boulder in the US.

“It is urgent that the World Health Organization and other public health agencies adapt their description of transmission to the scientific evidence so that the focus of mitigation is put on reducing airborne transmission,” Jimenez said.

The team, led by researchers at the University of Oxford in the UK, reviewed published research and identified 10 lines of evidence to support the predominance of the airborne route.

The researchers highlighted the super-spreader events such as last year’s Skagit Choir outbreak in the US, in which 53 people became infected from a single infected case.

Studies have confirmed these events cannot be adequately explained by close contact or touching shared surfaces or objects, the researchers said in their assesment.

They noted that transmission rates of SARS-CoV-2 are much higher indoors than outdoors, and transmission is greatly reduced by indoor ventilation.

The team cited previous studies estimating that silent -- asymptomatic or presymptomatic -- transmission of SARSCoV-2 from people who are not coughing or sneezing accounts for at least 40 per cent of all transmission.

This silent transmission is a key way COVID-19 has spread around the world, “supporting a predominantly airborne mode of transmission,” according to the assessment.

The researchers also highlighted work demonstrating longrange transmission of the virus between people in adjacent rooms in hotels, who were never in each other’s presence.

On the contrary, the team found little to no evidence that the virus spreads easily via large droplets, which fall quickly through the air and contaminate surfaces.

“We were able to identify and interpret highly complex and specialist papers on the dynamics of fluid flows and the isolation of live virus,” said study lead author Trish Greenhalgh.

“While some individual papers were assessed as weak, overall the evidence base for airborne transmission is extensive and robust,” Greenhalgh added.

He noted that there should be no further delay in implementing measures around the world to protect against such transmission.

The assessment has serious implications for public health measures designed to mitigate the pandemic, the researchers said.

They said “droplet measures” such as handwashing and surface cleaning, while important, should be given less emphasis than airborne measures, which deal with inhalation of infectious particles suspended in the air. According to the researchers, if an infectious virus is primarily airborne, someone can potentially be infected when they inhale aerosols produced when an infected person exhales, speaks, shouts, sings, or sneezes. They noted that some airborne control measures include ventilation, air filtration, reducing crowding and