WHO acknowledges COVID-19 airborne transmission may be possible

The World Health Organization’s (WHO) acknowledgement came after more than 230 scientists called on health authorities to address ‘every potentially important’ transmission pathway in order to slow the spread of COVID-19.
 
Many epidemiologists have been hesitant to label coronavirus as ‘airborne’, as there is no evidence it is able to spread in a similar manner to highly infectious diseases such as measles, which can linger in the air for hours and is estimated to be up to six times more contagious.
 
Nonetheless, the WHO’s technical lead for COVID-19 Dr Maria Van Kerkhove told reporters that microscopic respiratory droplets are a possible route for infection.
 
‘We have been talking about the possibility of airborne transmission and aerosol transmission as one of the modes of transmission of COVID-19,’ Dr Van Kerkhove said, before adding that the WHO is still collecting evidence and will soon publish a scientific brief on the virus’ modes of transmission.
 
ANU infectious diseases physician and microbiologist Professor Peter Collignon believes there is the potential for airborne spread in specific settings, but told newsGP he does not want the risk to be overstated.
 
‘You can come up with a laboratory experiments that show these aerosols stay in the air … but the epidemiological data, the follow-up data, show that this mainly spreads when you’re close to people for long periods of time, particularly indoors when there’s [poor] ventilation,’ he said.
 
‘If aerosols were a big feature with this, [if there were infected] people in the same household, you’d expect to have 70%, 80%, 90% infection rates, but instead it’s closer to 10% or 20% of the house.
 
‘[This] is good news because if it really was spread a lot with aerosols … we’d all either have to be in spacesuits or not breathe for the next three years.’
 
However, UNSW respiratory physician and epidemiologist Professor Guy Marks, who contributed to the open letter, told newsGP its contents are simply focused on lowering the risk of coronavirus spreading in general.
 
‘Recognising the role of smaller particles, transmitted by the airborne route, focuses attention on ventilation, air exchange rates and the indoor environment,’ he said.
 
‘It remains unclear how important [safeguards like masks] are. Where there is widespread community transmission, it does seem a wise addition to other measures, mainly to protect others from the wearer.’ 
 
The WHO’s technical lead for infection prevention and control Dr Benedetta Allegranzi acknowledged there is ‘emerging evidence’ of airborne transmission, but that it is not definitive.
 
According to Dr Allegranzi, part of the ongoing review of evidence will be aimed at understanding the importance of transmission by aerosols compared with larger droplets, as well as the dose of the virus needed for infection from aerosols.
 
‘The possibility of airborne transmission in public settings – especially in very specific conditions, crowded, closed, poorly ventilated settings that have been described – cannot be ruled out,’ she said.
 
‘We have to be open to this evidence and understand its implications regarding the modes of transmission and also regarding the precautions that need to be taken.’
 
Professor Collignon, who is also a member of Australia’s Infection Control Expert Group, has ‘no trouble’ with people calling for adequate ventilation as ‘all the data’ show that being outdoors is much safer than indoors.
 
But he said Australia’s success at reducing the coronavirus’ R number to less than one using already established infection control procedures shows there is currently a limited need for other enhanced protections, such as P2 or N95 masks.
 
‘What [predominantly airborne transmission] would mean is that everybody’s got to be wearing N95 masks all the time and doing it properly. Well, the probability of that’s low,’ he said.
 
‘My view is, let’s … do what we can in a practical way that really decreases transmission. I fully accept it may not decrease it to zero. But what this is about is getting the effective R number below one and at low numbers and keeping it there.
 
‘The bottom line is this virus is not going to go away. So whatever we do, we’re going to have to do for the next two or three years.’
 
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