World Health Organization reviewing evidence on airborne transmission of Covid-19

Henrietta Brewer
July 7, 2020

However, the World Health Organization has denied the research claims saying the evidence was not convincing.

If it can hang in the air for long periods of time, even after an infected person leaves that space, that could affect the measures healthcare workers and others take to protect themselves.

Four studies sent to the White House by the American Academy of Science in April point out the virus can infect individuals through mere breathing, not only via droplets sprayed by sneezing or coughing. The rapid spread of the virus sparked many studies that looked at the length of time these virus-laden aerosols could stay in the air.

According to the NYT, in an open letter to the agency, which the researchers plan on publishing in a scientific journal next week, 239 scientists in 32 countries have outlined the evidence showing that smaller particles can infect people. Scientists have found when the virus is present in droplets, it remains able to infect people for at least three hours.


"At typical indoor air velocities, a 5-micron droplet will travel tens of meters, much greater than the scale of a typical room while settling from a height of 1.5m above the floor".

"If we started revisiting airflow, we would have to be prepared to change a lot of what we do ..." Meanwhile, ventilation systems in schools, offices, residences and other public places may have to be thought out again to minimise recirculating the potentially virus-infected air.

Secondly, they should supplement "general ventilation with airborne infection controls such as local exhaust, high-efficiency air filtration, and germicidal ultraviolet lights".

However, WHO has said the evidence is not convincing enough. It stated that the issue of whether or not COVID-19 was airborne was of "heightened significance" as many countries stop restrictive lockdown measures.


Professor Morawska said several retrospective studies of the SARS epidemic had shown that airborne transmission was the most likely mechanism that explained the spatial pattern of infections.

While the researchers stressed that their findings do not prove that the virus spreads "in an airborne fashion", they said their observations did indicate that the disease might be spread though both direct (droplet and person-to-person) as well as indirect (contaminated objects and airborne transmission) contact. Dr. Benedetta Allegranzi, the WHO's technical lead on infection control, said the evidence for the virus spreading by air was unconvincing. But airborne transmission via smaller particles is possible in some circumstances, such as when performing intubation and aerosol generating procedures, it says.

Dr. Benedetta Allegranzi, a World Health Organization expert on infection prevention, said that a large majority of the group of more than 30 worldwide experts advising the United Nations agency has "not judged the existing evidence sufficiently convincing to consider airborne transmission as having an important role in COVID-19 spread". "We are arguing that there is insufficient proof that aerosol/airborne transmission does not occur", he said.

McKee noted with the UK's recent reopening of its pubs, restaurants and salons, the possibility of airborne coronavirus transmission might mean stricter interventions are needed indoors, including more mask-wearing and continued physical distancing.


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