Expert reaction to reports that the WHO have said airborne transmission of SARS-CoV-2 cannot be ruled out in crowded, closed or poorly ventilated settings
It has been reported that the World Health Organisation (WHO) have said airborne transmission of SARS-CoV-2 cannot be ruled out in crowded, closed or poorly ventilated settings.
Prof David Heymann, Professor of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, said:
“SARSCoV2 is thought to transmit in droplets generated through a cough, sneeze or by speaking, shouting, and singing. There are two types of transmission of the SARSCoV2 that are well understood – direct droplet contamination either from one person to another face to face, or droplet contamination of a hand that then touches the eyes, nose ore mouth; or aerosolization when a virus containing droplet is propelled between people within approximately a meter of each other through an aerosol – a temporary suspension of the droplet in the air. In all instances the virus is contained in a droplet and remains infectious as long as the droplet remains intact.
“Airborne transmission is a type of aerosol transmission, and is thought to occur with some types of respiratory virus infection (e.g. measles) when aerosols containing droplets that surround the virus are picked up in an air current that moves the aerosol farther than in direct or simple aerosol transmission.
“This could theoretically occur with SARSCoV2 if the aerosol is recirculated by a fan or another air circulating system such as an air conditioner, but this has not been proven and research to better understand whether this occurs is underway to see if it does occur, and if so to determine whether the droplet surrounding the virus remains in tact.
“There is some laboratory evidence that aerosols containing droplets with SARSCoV2 can be transmitted greater than 1 meter, and this evidence is now important in hypothesising how and if this might occur among humans, and if so then we’d need to prove that it does occur in the current situation of the pandemic.
“There is also evidence that outbreaks of SARSCoV2 can be contained by track and tracing methodologies, and that those contacts who self isolate decrease transmission to others – suggesting that if airborne transmission is occurring it is not a major means of transmission.
“Animal model studies might be useful in gaining better understanding as well, and the hamster is an animal that can be infected with SARSCoV2. Placing hamsters in situations where airborne transmission is being assessed could add information, but the final need is to continue to collect evidence that would be needed to prove that airborne transmission of SARSCoV2 occurs among humans.”
Prof Keith Neal, Emeritus Professor of the Epidemiology of Infectious Diseases, University of Nottingham, said:
“Aerosol transmission cannot be ruled out but we need to know which routes – droplets, aerosols or surface contamination – are important as an infection risk. Until we do social distancing, cough etiquette and hand washing remain important.
“We may move to more face coverings indoors but the evidence isn’t there yet.”
Dr Shaun Fitzgerald FREng, Royal Academy of Engineering Visiting Professor at the University of Cambridge, said:
“The advice which was drawn up by CIBSE several weeks ago regarding ventilation was fundamentally based on taking a precautionary approach to the potential airborne transmission route. Ensuring spaces occupied by multiple people are well ventilated remains sound advice.”
Source: UK SMC
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