New Delhi, April 16: There is consistent, strong evidence to prove that the SARS-CoV-2 virus, which causes Covid-19, is predominantly transmitted through the air, according to a new assessment published in the medical journal The Lancet.
A multi-research team from the UK, US and Canada warned that public health measures that fail to treat the virus as predominantly airborne leave people unprotected and allow the virus to spread.
Silent (asymptomatic or presymptomatic) transmission of SARS-CoV-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," as per the assessment.
By contrast, the researchers found little to no evidence that the virus spreads easily via large droplets, which fall quickly through the air and contaminate surfaces.
"The evidence supporting airborne transmission is overwhelming, and evidence supporting large droplet transmission is almost non-existent," said Jose-Luis Jimenez, chemist at the Cooperative Institute for Research in Environmental Sciences (CIRES) and University of Colorado Boulder.
"It is urgent that the World Health Organisation 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.
Further, the researchers emphasise that while it is necessary to wash hand and clean surfaces, they should be given less emphasis than airborne measures.
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.
The airborne control measures include ventilation, air filtration, reducing crowding and the amount of time people spend indoors, wearing masks whenever indoors (even if not within 6 feet or 2 metres of others), attention to mask quality and fit, and higher-grade PPE for healthcare and other staff when working in contact with potentially infectious people.
The team reviewed published research and identified 10 lines of evidence to support the predominance of the airborne route.
At the top of their list: Super-spreader events such as the Skagit Choir outbreak, 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.
Moreover, transmission rates of SARS-CoV-2 are much higher indoors than outdoors, and transmission is greatly reduced by indoor ventilation.
The researchers also cited work demonstrating long-range transmission of the virus between people in adjacent rooms in hotels; people who were never in each other's presence.