A report published in the The Lancet has dismissed the predominant scientific view that the novel coronavirus is not an airborne pathogen. In fact, the new assessment in the medical journal has found “consistent, strong evidence” that the SARS-CoV-2 virus, which causes Covid-19, is predominantly transmitted through the air.
The report has been written by six experts from the UK, USA and Canada, including Jose-Luis Jimenez, a chemist at the Cooperative Institute for Research in Environmental Sciences (CIRES) and the University of Colorado Boulder. The team of experts, led by the University of Oxford’s Trish Greenhalgh, reviewed published research and identified ten lines of evidence to support the predominance of the airborne route.
At the top of their list is the occurrence of super-spreader events where a single infected case can lead to a full-blown outbreak of the infection. Studies have confirmed that 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. Reacting to the news, Dr Rakesh Mishra, Director, CSIR-CCMB, advised, “Don’t remove masks in any public places and don’t gather in a cluster in a closed environment where there is no air flow. The WHO has also issued an advisory saying that the virus can hang in the air for up to two hours, particularly when there is no airflow. We have ignored such things which is why we are going through this pandemic.”
The team also highlighted research estimating that silent (asymptomatic or presymptomatic) transmission of the virus from people who are not coughing or sneezing accounts for at least 40% of all transmission and a key way in which Covid-19 has spread around the world, “supporting a predominantly airborne mode of transmission,” according to the assessment. The researchers also cited work demonstrating long-range transmission of the virus between people in adjacent rooms in hotels or people who were never in each other’s presence.
By contrast, 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 the live virus,” lead author Greenhalgh said. “While some individual papers were assessed as weak, overall the evidence base for airborne transmission is extensive and robust. There should be no further delay in implementing measures around the world to protect against such transmission.”
Putting forward their arguments, the team has called for modifications in Covid-19 protocols. “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,” said Jimenez.
The new work comes with serious implications for public health measures worldwide which have been designed according to “droplet measures”, such as handwashing and surface cleaning. While not unimportant, it was suggested that these be given less emphasis than airborne measures, which deal with the inhalation of infectious particles suspended in the air. Ideally, airborne control measures should include ventilation, air filtration, reducing crowding and the amount of time people spend indoors, wearing masks indoors (even if not within 6 feet of others), greater attention to mask quality and fit, and higher-grade PPE for healthcare and other staff when working in contact with potentially infectious people. “It is quite surprising that anyone is still questioning whether the airborne transmission is the predominant transmission pathway for this virus or not,” said co-author Professor Kimberly Prather, an aerosol scientist from the University of California San Diego. “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. The world needs to follow their lead as soon as possible.” WITH ANI INPUTS
