Decisions on COVID-19 made by governments and the World Health Organization may literally be life-or-death and yet political leaders have made avoidable errors and misused ‘scientific data’, respected medical scientist Professor Robin Wood told a PPS Webinar. The bungling regarding the airborne transmission of the coronavirus is an example.
The importance of drawing on the best possible research and evidence is understood in the world of science, writes Karen MacGregor. There has been an international “groundswell of opinion” among leading infectious diseases experts that the world should be taking seriously the dangers of airborne small particle transmission of COVID-19 – but is not.
WHO and many governments, including South Africa’s, have focused disease prevention actions on two means of transmission: indirect transfer of the virus from surfaces, called fomite transmission; and person-to-person transmission via respiratory droplets produced by sneezing or coughing.
Wood is director of the Desmond Tutu Health Centre in the Institute of Infectious Diseases and Molecular Medicine at the University of Cape Town. He was speaking at a webinar on 28 July, hosted by PPS – Health Professions Indemnity, MedicalBrief and the Desmond Tutu Health Foundation and attended by more than 600 participants.
Titled “COVID-19 transmission – An absence of data”, this was the third in a five-part webinar series investigating research and developments relating to COVID-19. The series is moderated by MedicalBrief Managing Editor William Saunderson-Meyer.
Emeritus Professor of Medicine at UCT, Wood has been a visiting fellow at Harvard Medical School and honorary professor at the London School of Hygiene and Tropical Medicine and served on international scientific advisory boards including those of the World Health Organization, International Aids Society, TB Vaccines Initiative and Gates Foundation.
He is conducting ground-breaking research into disease transmission at UCT’s Aerobiology and TB Research Unit, and leads the scientific research group of the SA Medical Research Council and its flagship programme investigating the aerobiology of TB transmission.
There is an absence of data on COVID-19 transmission. What are the current issues around fomite, airborne and aerosol transmission?
The global response to coronavirus transmission has been confused and lacking a large body of research, data and technologies. But from the start, Wood has been correctly warning of aerial small particle transmission.
The World Health Organization or WHO, which is leading the global response to the COVID-19 pandemic, produced infection control guidelines. The South African government also published guidelines, which Wood was sent in April.
The guidelines of both cited only two routes of transmission – via surfaces and in large respiratory particles. “I found that difficult, in that people don’t cough and sneeze in other people’s faces sufficiently often to drive a pandemic like this,” said Wood.
The WHO made a statement saying no small particle airborne transmission of the coronavirus had been recorded, except during aerosol generating procedures in close proximity. “Then there was a throwaway phrase that in an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported. That sounded pretty impressive.”
Wood studied the WHO statements, reports and references and found seven references used to justify the position. “The first five didn't actually mention the means of transmission. The sixth one was from the WHO’s study of the COVID-19 epidemic in China, conducted very early one; that’s where the large numbers were quoted from.
The problem was that when Wood checked with the Chinese CDC – the Chinese Center for Disease Control and Prevention – they did not actually say COVID-19 was not transmitted by aerosols: “They raised the possibility and said ‘we don't know’.”
“And then the last reference was quite amazing,” said Wood. A researcher looking at patients in a Singapore hospital found COVID-19 RNA on an extraction vent. He did not find the virus in the air, but did suggest it was transmitted through the air to the vent. “So he actually came to the opposite conclusion,” Wood said.
“It shows that when you have a hypothesis and you want data to fit it, people can manage in some way to stretch it. To my mind, that was a misrepresentation of the references [WHO was] quoting.”
Have there been challenges been to this?
There was a preliminary 4 April 2020 report from the National Academies of Sciences, Engineering, and Medicine in the United States. “This is a pretty impressive group of people,” Wood said.
“They came to the conclusion that while current SARS-CoV-2 specific research is limited, the results of available studies are consistent with aerosolisation of the virus from normal breathing.” Those scientists were prescient.
Later, there was a paper by a scientist Wood holds in high respect: Professor Lidia Morawska of Queensland University of Technology in Australia.
She co-wrote a paper with a Chinese CDC scientist, called “Airborne Transmission of SARS-CoV-2: The world should face reality”, published on 22 June 2020. Wood sent her paper to the SA Department of Health, and questioned the guidelines they had produced.
“Everybody sort of ignored that and it went away.”
Then Morawska joined with a top aerosol scientist from Johns Hopkins University, and they wrote an open letter which was signed by 238 leaders across the world. They appealed to the medical community and national and international bodies to recognise the potential for airborne small particle transmission of COVID-19.
They wrote: “There is significant potential for inhalation exposure to viruses and microscopic respiratory droplets, micro droplets, at short to medium distances, up to several meters or room scale. And we are advocating for the use of preventative measures to mitigate this route of airborne transmission.”
So there is a growing swell of opinion questioning the international guidelines.
South Africa has set up a special advisory group in order to see if its guidelines should be changed. It now appears as if “WHO is preparing is the ground to backtrack a little”, said Wood, and might grudgingly allow airborne transmission to be considered.
How particle transmission works
Wood described a study a couple of years ago of speech, involving patients who spoke four different languages. They were asked to speak at some eight intensities and the particles emitted were measured. “This comes back to what the special group from the National Academies found, which is that normal breathing could be a cause.”
The study showed that particles are produced in the periphery of the lung, which has no flow but opens and closes with each breath. The surface area of the peripheral lung is large – the size of a tennis court. “As these bellows open and close, they are covered in surfactant, a detergent which allows the surface tension to be controlled, and that produces droplets,” Wood explained.
“By far and away the largest number of particles are in the range of one to two microns.” This is important, because that small size particle will go straight down the lungs if someone breaths them in, and will have a high chance of being retained in the periphery of the lung.”
Aerosol scientists believe that small particles are produced by every respiratory activity, such as during inspiration as the peripheral lung is expanded. “If you cough, if you speak, if you just take deep breaths, you will produce particles of between one and 10 microns, and most will be one to two micron in size. That's just normal breathing activity.”
To that can be added other particles, for example produced by loud singing or letters such as Ps or Ts. A cough increases the speed of particles that come out.
“We’re very interested in the one to two micron particles because they're the ones that get into the lower lung.” Larger particles, between five and 10 microns, come out of the mouth as exhaled air, “in a in a sort of cloud which has a high humidity”.
“As that cloud dissipates, each of those particles will lose some of its liquid as it moves into a drier atmosphere. So even those particles from five to 10 micron, can in fact become one to five micron. The concept that normal activities of breathing don't produce potentially dangerous aerosols just doesn't fit with the data.”
Wood’s research in Cape Town “100% fits” with the size particles from the study of speech. “So if I get people to just breathe normally, to take coughs or to take very deep breaths in and out, if I calculate the number of particles produced per minute, they're all much the same, because it's dependent on the amount of air that you breathe in.”
What are some of the consequences of aerosol transmission?
A primary consequence is raised levels of COVID-19 transmission and infection, and indeed the coronavirus has proved extremely infectious.
“There's no doubt that there have been a lot of cases of asymptomatic patients transmitting the disease. That means they're not coughing and sneezing. So they have to be transmitting by some other means,” Wood argued. In a case in Mongolia, a person contracted COVID just by regularly walking past the open door of somebody with the disease.
Viral RNA has been isolated from air in hospitals. There have been studies in Singapore, Korea and Nebraska, and there is increasing evidence that transmission is taking place over longer distances than would be the case for large particles spread by sneezing or coughing.
Particle production is very consistent within individuals – but very different in different people. “So there is a lot of variability and this certainly raises the possibility that super-spreaders may be people who produce many more particles than others.”
Wood once calculated that it is possible to get a billion viral particles into a 50-100 micro meter droplet. In which case, it becomes important to know what is the infectious dose – but that is not really known.
While the WHO said it had not seen SARS-CoV-2 survive in the air, it has been shown to remain viable in a hospital environment, and in a laboratory environment for up to 16 hours. It is technically difficult to measure particles, which also change size depending on humidity and temperature. A Nebraska study found that a live virus isolated in the air was able to infect cells.
Given airborne transmission, what practical actions would limit its spread?
Wood said that with small particle transmission, social distance remains important because of the rapid dilution of particles with distance. There is some data that viral particles can be carried on air currents, “so you have to consider direction and currents”. Finally, if a droplet nuclei can remain airborne for a long time, it becomes necessary to try and dilute the droplets or destroy them with ultraviolet light or by some other means.
“In different scenarios, we're going to have to consider different modalities of transmission.”
Transport is a particular worry, Wood continued, with cases of transmission within vehicles and planes. One anomaly is that often ventilation comes from above, aimed downwards. Yet the natural way to get rid of particles, because of the heat factor, is for them to move upwards. “Having downward movement of air could actually make things worse.”
With airborne transmission of virus particles, being indoors with other people close by is risky. And being in a poorly ventilated area sharply raises the risk of infection from droplet nuclei. “Probably 90% of transmission is taking place indoors. Outdoors, the dilution factor is so massive that if you're more than a metre away, transmission is highly unlikely.”
Research by Aalto University in Finland into the aerial spread of SARS-CoV-2 concluded, among other things, that busy poorly ventilated indoor spaces should be avoided. This is sensible, said Wood, who wears an N95 mask if he goes somewhere he believes is poorly ventilated.
He is in a high risk group. However: “Part of the reason is that I live in the city that has more TB than the whole of the United States and Europe put together. And the risk to my life of acquiring TB is much higher; it is a 4% mortality rate for normal TB, let alone multi-drug resistant TB. We live in an environment where ventilation should be taken more seriously.”
What about thinking around schools and taxis?
Wood believes societies have lost some of the messages learned historically in schools. For instance, low windows are used that produce air currents that move particles horizontally, rather than high windows that move the plumes of hot air people produce up and out of the room.
“There’s a lot we could do on ventilation of these spaces. The problem is that we don't have enough time to do that,” he added.
“The next question is how infectious are young people, and what age are they likely to get the disease and what age are they likely to be able to spread it? Icelandic studies have shown that younger children don't seem to be as infectious. But the data is thin on the ground.”
Regarding taxis: “If I were to try and design something which I thought was the most efficient transmitter of this type of disease, it would be a taxi,” Wood said.
“Their saving grace is that they have very large doors which open at regular intervals. So that does increase the ventilation. And the other one is the exposure time, which is relatively short because of the short distances travelled. But a closed box going to the Eastern Cape and back would be pretty dreadful from my point of view.”
“So obviously, you can triage people to try and keep the most infectious people out; the ones with temperatures and symptoms. You can try and decrease the air plumes coming out of people with cloth masks. But ventilation is going to be critical and the number of people in the vehicle is going to be critical as well.”
What should South Africa be doing in terms of policy determinations?
“What is the exit strategy for all this?” Wood responded. “Are we going to try and stop transmission by social distancing indefinitely? Are we going to do it for a period of time until we get a vaccine? A vaccine seems a hope but is not necessarily going to happen.
“Will we try to protect individuals at risk with passive immunity, which I think would be a nice solution. You'd watch the epidemic and as another peak starts developing, you would protect the vulnerable population around there with a relatively short-lived policy.
“But key to this pandemic has been the impact on the Westernised style of hospitalisation,” Wood said. The big fear has been overwhelming health systems and facilities.
It has become clear that health care workers have not been protected adequately. This is illustrated in the UK, for instance, by high infection rates among doctors in London teaching hospitals. The same is likely the case in South Africa.
“The rationale for not giving N95 masks was purely economic, and purely short supply in the early days. It wasn't the right thing to do, it was the pragmatic thing to do.” Protecting health care workers should be a priority for all countries, Wood stressed.
COVID-19 – Exceptional or ‘normal’?
Previously, Wood postulated that exposure to animal coronaviruses – of which there are hundreds – may give some immune protection.
His insight came from discussions with his son, who is a vet, on the compartmentalisation of medical and veterinary sciences and how they rarely interrelate. Talking about how common animal coronaviruses are and how they present in different animals, they developed a hypothesis about vets building virus immunity.
“We did a quick rough-and-ready survey of veterinary surgeons to see if they seemed to have a low infection rate for COVID-19, and it certainly seemed that way,” said Wood.
“We live on this planet in a sea of other organisms, all of which are competing, and our immune system is competing with them all the time. It seems unlikely that a family of viruses would suddenly jump up which has no relationship to any other members of the family.”
For instance, of the seven known human coronaviruses, three have the same spike protein and binding to ACE2 receptors, the protein in the body that provides the entry point for the virus to hook into and infect human cells.
Wood’s supposition appears supported by new research, published in Nature, that uncovered the presence of virus-specific T cell immunity in people who have recovered from COVID-19 or SARS – as well as in some people who have never been infected by either virus.
The findings suggest that exposure to coronaviruses induces long-lasting memory T cells. This could assist in the management of the COVID-19 pandemic and vaccine development.
It can be helpful to look at the world within the spectrum of other things occurring, rather than applying exceptionalism, Wood believes. “This fits with a philosophy of a multiplicity of organisms. Our immune system is reacting to them, and they're trying to find little niches. “It's an ongoing battle.”
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