COVID-19 predominantly transmitted through air: Lancet study cites 'strong evidence'

New Delhi: Strong evidence has come to fore that the SARS-CoV-2 virus, behind the COVID-19 pandemic, is predominantly transmitted through the air, according to a new assessment published in The Lancet journal on Friday (April 16). The report said that 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," Jose-Luis Jimenez, from the University of Colorado Boulder in the US, is quoted as saying by a PTI report.

"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 added.

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 from the UK, the US and Canada 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.

The researchers said that studies have confirmed that these events cannot be adequately explained by close contact or touching shared surfaces or objects. They also observed 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 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," said the assessment. The researchers also highlighted work demonstrating long-range 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, adding "While some individual papers were assessed as weak, overall the evidence base for airborne transmission is extensive and robust."

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

The researchers said that the assessment has serious implications for public health measures designed to mitigate the pandemic, adding that "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 the amount of time people spend indoors.

Wearing masks whenever indoors, attention to mask quality and fit, and higher-grade PPE for healthcare and other staff when working in contact with potentially infectious people are some of the other control measures, according to the researchers.

"It is quite surprising that anyone is still questioning whether airborne transmission is the predominant transmission pathway for this virus or not," said study co-author Professor Kimberly Prather, from the University of California San Diego, US.

Prather further said, "Only by including inhalation of aerosols at both close and long range can we explain the many indoor outbreaks that have occurred around the globe. Once we acknowledge this virus is airborne, we know how to fix it."

There are many examples of places that have fared much better by acknowledging this virus is airborne from the start, said the researchers, adding that the world needs to follow their lead as soon as possible. 

(With Agency Inputs)