 Hello and welcome to NIST today in talking science and tech. We will be looking at the issue of different modes of transmission of the COVID-19 virus that is SARS-CoV-2 virus. Since the beginning of the pandemic there has been debate about whether this virus is only transmissible through droplets which can only travel up to six feet or is airborne transmission also possible that is through aerosols which can travel longer distances. So just a couple of weeks back the World Health Organization and the Center for Disease Control in the US did admit, did recognize that in fact airborne transmission is possible. So today we are joined by Pravir Purkayastha who will be talking to us about this about what led to this conclusion why did it take a whole year since the beginning of the pandemic and what implications will this have for the future for our indoor spaces indoor infections and the wearing of masks etc. So Pravir can you first tell us you know why it took a whole year for these major bodies, health bodies of WHO, the CDC to recognize that aerosol that airborne transmission is happening for COVID-19. You know this was quite well understood by the lay public as well that airborne transmissions were happening but why did the technical bodies like CDC and WHO take so long and I think there was a huge amount of misunderstanding between those who study aerosols, airborne particles as a matter of physics and this is really something which engineers and physicists do study and those who are doctors and because they came from two different disciplines it appears that their use of words might have been the same but they really were not talking of the same phenomenon or the same set of issues. So droplet in physics does not mean that it is of a certain size alone. It's really that it is something which has a size and it can also float in the air for how long it floats that's a separate question and that depends on not just its size but depends on number of other issues as well. So the droplets and for the medical community seem to mean that it's basically a liquid particle. Now if you take this issue of how people see it that clinical practitioners doctors the health community they seem to believe that particle less than 5 micron is not airborne for long periods and it deposits quickly on the ground within 1 to 2 meters distance particle will fall rapidly to the ground if it is more than 5 micron in size. The reality is that it can be airborne for quite some time and it depends on a number of other issues partly also is there a certain air current in the place and even if you're sitting inside a room there are air currents which are there and typically the 5 micron particle about 5 to 8 micron 5 to 10 micron does not fall to the ground within 1 to 2 meters of the source it in fact can travel some distance depending on other other conditions and it can also stay a float for about 10 minutes at least 10 minutes and under some conditions 5 micron particle can stay in the air for an hour and if there is a current of air it can even stay longer. So this whole understanding that 5 micron is the critical size above which a particle falls to the ground rapidly was something with the medical community seem to hold but it wasn't something which the aerosol community and I mean physicists and engineers were in agreement with but unfortunately in this particular case the decisions were being made made by the health community. So though they were speaking the same words they did not mean the same thing. So this is one communication gap which existed in the two communities when we look at the genesis of this issue it seems that most of the research which the medical community had accepted as de facto size related was not related to size it was really related to tuberculosis infection and tuberculosis infection is a particular case where the particle has to penetrate this particle has to penetrate deep into the lung and because of that if it is less than my 5 micron it does penetrate it's larger than 5 micron it doesn't reach that part of the lung which the TB particles are actually infect the patient. So given that 5 micron was not something which was the property of the aerosol but the specific issue of tuberculosis infection but unfortunately for the medical community they sort of identified the 5 micron is something below which it's a drop above which it's a droplet above which it will fall to the ground in a very short distance and therefore it's a droplet and not an aerosol while to the community of physicists and engineers this was not true and they knew from their own studies that this could aerosols could be larger than 5 microns droplets come in a number of sizes and it does stay airborne and it does travel much longer distances than 1 to 2 meters which was thought to be the critical issue. So therefore for most of the WHO CDC experts they believe that there that it is a droplet falling on surfaces which is the main reason for the infections while the community of others who are also dealing with it believe that given certain examples and there were certain examples which everybody knew about a restaurant in Guangzhou a particular choir practice which is done by musicians all of it would have indicated that this is not actually true but nevertheless old beliefs dry you know take a long time to go and unfortunately in this particular case that's what seems to have been the confusion and only after it was traced why this is wrong it was traced to the original articles and research is done 60 years back that finally this issue was put to bed very reluctantly and it took much longer than it should have by both CDC and WHO it took a year which is very very surprising because all measures that we started taking would have indicated that this facts that will be talked about by both CDC and WHO are not correct and it also had an impact initially on masking that how effective the masks are you'll remember there are a lot of controversy my masks are not effective because the virus is a very small particle and it can go through most masks but the point was that the virus doesn't travel as an individual particle it's generally in a coating of liquid mucus and other stuff and therefore it is carried in a much larger particle and that is caught by the masks even the cloth masks that we started using so this this wisdom took a much longer time to be accepted within CDC and WHO particularly the health groups which were concerned about it and who were actually doing this passing most of these regulations and directives of what should not be done so it is also a gap that we as a technical scientific medical community tend to have that we don't use the same words but we don't go into the basis of what these words really mean for each of the community so you get basically a cognitive gap because you're saying apparently the same thing but actually you are not so probably now that we know that airborne transmission is happening and it's finally been accepted by WHO CDC and all these leading bodies so now that we're you know opening up again if you look at the situation in India the lockdowns are getting sort of easing down now what are the sort of precautions that need to be taken by the people we can we go back to normal or what sort of changes do you think will have to be made so now that we know aerosol transmission takes place and it should also put to bed the whole controversy about mask or not to mask no India it was never a very strong controversy this is much more than the US phenomenon that people felt asking me to put on masks is an infringement my of my fundamental right to infect others so that that that was never an Indian or a you know in large parts of the world this is never the issue but the question is that you cannot go back to normal if you go back to normal of course you have to accept the fact that again infections will start to grow and infections obviously have not gone away you could look at different parts of India at the moment we are still at middle or tail end of the third wave some places numbers are still going up but even when numbers are falling and if you accept that you don't catch all the infections you catch probably the actual infections could be anything from three to ten times these are the figures people are saying not my figures so if you even if we take that the figures of actual infections are much larger partly because asymptomatic cases and partly because mild infections etc people may not actually go and get themselves tested so given that there is going to be a risk of infections and the numbers growing again so how do you prevent that so obviously you have to now impose rules of different kinds and it is clear from the recommendations itself that if you are in a place where the air is being diluted continuously then your chances of infections are less therefore closed spaces are the problems so certain kinds of activities therefore are going to be difficult unless the numbers really come down which is where you have per se closed spaces which is of course the cinema halls large congregations gathering in say temples churches and mosques those are the places you do have large numbers gathering in closed proximity and there would be then possibilities of infection from there you also have the gyms and indoor dining even these are going to be problems so if you want to open up you will have to open up in a way taking this into account and phase wise opening of the place last being when the numbers are really low only then going to include space so that is one thing that we have to take into account the need for masks that you have to still continue to use masks you have to mask up for others others have to mask up for you even when you sit at home if guests come you have to keep your doors and windows open so those are minimum precautions we need to continue taking so that is one part of it and the second part of it and this is a much more long term problem is how to engineer buildings indoor spaces itself and I think that's a much larger question we also need to address yeah exactly so what are the sort of changes that in the future we'll have to look into making into our spaces such as indoor spaces like work spaces offices you know what are the changes particularly in terms of the ventilation that we'll have to look into making well I think this is a very important landmark in our lives that we've also understood for example the flu infections that takes place every year now why does it take place for instance in India in the monsoon seasons and why does it take place in winters for instance in Europe and America and I think the answer is now very clear because these are the periods when people stay indoors much more and therefore they infect each other in monsoons we don't go out that much we are much more indoors and therefore the infections spread more readily and of course this is what happens also the United States for example North America or in Europe now it's also interesting this time the flu has been much less the in fact the number of flu cases which also show up as pneumonia cases and lead to death for older people that has been much less this time but the same reasons that we are talking about the fact that social physical distancing has been imposed places where your indoors has been where large numbers of people can meet has been stopped so I think this will also have a lot of implications for all infectious diseases which are airborne so I think this has laid or put at least in front of us the key issue that how do you engineer particularly the work spaces because that's where you do meet people and much more and if there is one person who comes to office who's infected of course the number of people will get infected the consequence so one is the fact that you need to have far better ventilation in these spaces so we have been doing our air conditioning based on the fact the exchange of air fresh air is kept to a minimum because that reduces our energy costs I think what we also now recognize our energy cost will increase because our air conditioning needs a lot of exchange of fresh air and also it should also give a continuous flow of air inside the buildings so that has to be carefully engineered how air flows do take place and also filters because even within the offices you can use what are called HEPA filters and they filter out a lot of the vaccine virus load that is there in the air this is also one of the problems people didn't understand how HEPA filters work and how they can actually take out virus particles from the air even though it may not appear that the mesh that it uses the filters uses is is much larger than the size of the virus so how does it filter it out that's because people don't really understand the mechanics of the HEPA filter but as we now know HEPA filter can take a very significant part of the virus load out of the air so in any of the indoor spaces of this kind we need to also use HEPA filters to continuously filter out the air it's all of it is going to add to expenses therefore there is going to be much larger expenses for air conditioning ventilation ventilation we need to reason design all this where a large number of people gather and that means also the eating places it also means the gyms for example it also means of course the cinema halls masks whatever we are talking about churches etc and though they are much larger spaces so doing it there is not going to be that simple but it is also possible to provide ventilation much better ventilation and flow without air conditioning as well so you could have different levels at which you address these issues but they need to become a part of our public health issue and how we engineer the indoor spaces as far houses are concerned in India we have to accept that there are a huge number of people who stay in places which are going to be very poor in terms of ventilation and therefore the only solution is to provide of course at the moment at least that there should be windows windows and doors need to be kept open but again at night that's not possible so these are limited things that can be done but it also brings up the issue of housing itself that we need to consider housing for the people as a fundamental right and that needs to come back to our agenda and when it does then of course what is the kind of housing we need that all those should be put but even in the middle class areas when you build houses our attempt is to make or maximize the room space and not consider ventilation and light as a very important part of what we should build so all those things will have to be baked into the rooms itself of how buildings and all the spaces are constructed so we need to take a very you know careful look at all the standards that we have built for all of these issues so thank you for being for joining us today and that's all the time we have keep watching news click