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THE HEALTH | JUNE-JULY , 2021
| Covid-19 |
Overlooked toolbox in Covid-19 management
There is the possibility of long-range virus transmission in poorly ventilated and / or crowded indoor settings
THE SCIENTIFIC evidence accumulated for more than a year of the Covid-19 pandemic now more conclusively points towards the predominant airborne nature of its transmission that covers longer distances (> 5 feet ) and extended time of suspension in the air ( Figure ).
To date , this important feature of the infection spread received only cursory attention from authorities and policymakers worldwide and more so by the general public . Therefore , our existing pandemic management measures focused solely on droplets and fomites transmission might be although extensive , yet suboptimal effort .
On April 15 , 2021 , one of the most reputable scientific medical journals , The Lancet , published an article titled “ Ten scientific reasons in support of the airborne transmission of SARS-CoV-2 ”. At about the same date , two other oldest top medical journals — The British Medical Journal ( BMJ ) and Journal of the American Medical Association ( JAMA ) published articles written in a similar vein .
The following is the summary of scientific reasons or facts listed by Professor Greenhalgh and her colleagues in The Lancet article , which strongly points towards the important ( if not even predominant ) role of airborne nature of Covid-19 transmission backed by accumulated scientific evidence .
Important factors
The first such factor is the presence of super spreaders and super spreading events — where one infected individual becomes responsible for infecting a large proportion of those present in the
SHAKEN , NOT STIRRED
BY DR RAIS HUSSIN
AND DR MARGARITA PEREDARYENKO same premise and not necessary within five feet from the index patient . Only the predominant airborne nature of transmission could adequately explain the frequency of such situations in the Covid-19 pandemic .
Second , in a New Zealand study by Eichler and team , the researchers , while methodologically combining genomic sequence analysis and epidemiologic investigation , have proven the possibility of airborne transmission between people in adjacent quarantine hotel rooms who were never in direct contact with each other .
Third , according to the latest estimates , asymptomatic individuals are responsible for transmitting close to 60 per cent of all infections . Asymptomatic individuals are not sneezing or coughing much .
Therefore , it is difficult to explain such a distribution of infections unless we consider the role of airborne transmission . The smallest particles ( droplet nuclei < 5 μm ) laden with the viable virus and capable of travelling long distances in the air are found to be exhaled even while low voice talking or just breathing .
Also , contrary to common belief , there is evidence that smaller droplets may carry higher virus concentrations than larger droplets . Donald Milton , with his colleagues , observed such regularity in the case of the influenza virus ( 2013 ).
Fourth , it is well established that the risk of Covid-19 transmission is significantly lower outdoors than indoors and in well-ventilated versus poorly ventilated indoor settings consistent with its airborne transmission .
Fifth , Covid-19 spreads were reported in hospital environments with protective measures explicitly designed to address large droplets concern but not the possibility of airborne transmission .
Six , scientist detected viable Covid-19 virus in the air samples in laboratory conditions for up to three hours . However , detecting viable airborne virus outside of the laboratory settings is challenging due to damage during sampling .
Empirical evidence
Authors also stress that other infections such as measles and tuberculosis , whose primary airborne route of transmission is undeniable by now , “ have never been cultivated from room air ”.
Seven , in Uppsala University Hospital , Sweden , scientists detected SARS-CoV-2 N and E genes inside the ventilation HEPA filters located far outside the range to be explained by large droplets transmission . In the said Sweden study , the researchers could extract only genetic material rather than viable virus due to sampling
Figure : Difference between droplet and airborne transmission . challenges described earlier . Eight , another scientific experiment supporting airborne mode of SARS-CoV-2 transmission has been conducted in the Netherlands . Jasmin Kutter and her colleagues have demonstrated transmission of SARS-CoV-2 to two of four indirect recipient ferrets and SARS-CoV to all four while eliminating the possibility of direct transmission between animals ’ enclosures .
Ninth , to the best of Professor Greenhalgh and her other reputable colleagues ’ knowledge , no study so far “ has provided strong or consistent evidence to refute the hypothesis of airborne SARS-CoV-2 transmission ” while empirical evidence of otherwise is piling up continuously .
Tenth , the authors demonstrate inconclusiveness of arguments that to date have been put forward in favour of predominant close-contact ( large droplets and fomites ) mode of Covid-19 transmission . A higher risk of close-contact infection does not prove that the Covid-19 virus predominantly transmitted in droplets and does not contradict the hypothesis about its airborne transmission .
There is evidence that exposure to the tiniest droplets substantially dominates exposure to large droplets even at the typical interpersonal distance of 1.5 – 2 metres ( Wenzhao Chen and colleagues , 2020 ).
Airborne transmission route
How convincing does all of this sound ? It must be compelling enough that even the World Health Organisation ( WHO ), on April 30 , 2021 , has updated the English version of its Q & A section with regards to Covid-19 spread between people by adding a para that underscores the possibility of long-range virus transmission in poorly ventilated and / or crowded indoor settings .
Note that previously WHO and the Centres for Disease Control and Prevention , although not outright denying the possibility of the airborne nature of Covid-19 transmission , solely emphasised the close-contact or short-range modes of transmission ( large droplets and fomites ).
The other two articles in BMJ and JAMA journals echo the proposition about SARS- CoV-2 likely having a predominant airborne transmission route . They also discuss the implications of this scientific finding for the effective non-pharmaceutical intervention .
Wearing masks , physical distancing , limiting indoor occupancy and crowded outdoor activities remain relevant measures to curb the infection either from direct contact with surfaces or droplets or from inhaling droplet nuclei . However , when we consider accumulated scientific evidence about Covid-19 airborne transmission , few concerns immediately arise about the sufficiency of the existing efforts .
Long-term measures
First , the engineering control of indoor air quality — ventilation and filtration — in our work environment , educational institutions , shopping malls , other recreational public spaces , and even our homes become essential . It is the pertinent question what are the current conditions of our ventilation and filtration systems in all these spaces nationwide ? Except for hospitals , they might be set for bare minimums and not designed for effective infection control .
The airborne nature of Covid-19 transmission would call for a thorough revision and upgrade of ventilation and