Millennium Post (Kolkata)

‘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

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