Coronaviruses are infectious viral diseases agents of zoonotic origin, typically with a genome of single-stranded RNA, that can infect humans and cause severe or acute respiratory syndrome, yet a study suggests that the SARS-coronavirus is only moderately related to other known coronaviruses, with analysis also indicating that they do not closely resemble any of the three previously knowns groups of coronaviruses.
Recent examples of coronavirus outbreaks include the SARS-CoV in 2003 and the MERS-CoV in 2012. Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) first emerged in 2002 in China and was subsequently first identified in 2003, where transmissions mostly occurred in health care settings due to the lack of adequate infection control precautions. Once appropriate infection control practices were implemented, the epidemic came to an end in July, 2003. SARS-CoV-1 infection typically causes severe symptoms related to the lower respiratory tract and viral isolation samples have suggested additional routes of transmission. MERS-CoV, which was first reported in 2012, had a strong capability to survive outside the body and could remain infectious for up to an hour after aerosolization according to a study.
Studies that suggest possible aerosol transmission of SARS-CoV-2
Although, according to the World Health Organization, SARS-CoV-2 can only be transmitted by contaminated surfaces or via droplets that fall within one meter, some cases also suggest the possibility of aerosol transmission in small and closed environments. A new study on the aerosol and surface stability of SARS-CoV-2 compared to SARS-CoV-1 that was published by the New England Journal of Medicine reveals that SARS-CoV-2 can stay suspended in the air for three hours, with a similar reduction in its infectious rate as that of SARS-CoV-1, and that properties of SARS-CoV-2 are very similar to those of SARS-CoV-1 in terms of its formation and stability of air particles. However, the affinity to human receptors of SARS-CoV-2 is ten times higher than that of SARS-CoV-1.
Another study carried out in China estimates that 86% of all infections went undocumented. This would help explain the rapid spread of the virus and also raises awareness on just how difficult it is to contain. Virologist and coronavirus specialist Dr. Wathelet says that more than 3000 medical staff were infected in China due to the absence of proper N95 or FFP2 masks, highlighting that while the surgical masks they were using instead protect against droplets, they do not provide sufficient protection against micro droplets.
Another study carried out in order to determine possible modes of virus transmission investigated a cluster of SARS-CoV-2 cases associated with a shopping mall in China. The study found that indirect transmission of the virus occurred, likely resulting via contaminated objects, or via virus aerosolization or by asymptomatic infected persons. It also suggests that SARS-CoV-2 might also spread through the airborne route and remain infectious for up to one hour after aerosolization.
The challenge of evolving virus mutation
Another important consideration is that SARS coronaviruses could possibly evolve a greater ability to evade the host immune response, according to a study identifying such mutants exhibiting this ability. Virologist and coronavirus specialist Marc Wathelet says that the evolution of the virus can most effectively be addressed by hydroxychloroquine as it targets the host cell rather than the virus itself, making it difficult for the virus to escape it. He also calls attention to the most important difference of SARS-CoV-1 and SARS-CoV-2, which is that as opposed to SARS-CoV-1, SARS-CoV2 transmits also as an aerosol.
Professor Donald Milton, Professor of Environmental Health at University of Maryland School of Medicine : “Given there are now several reports of the presence of SARS-CoV-2 in respirable aerosols and on exhaust vents, indicating potential airborne infection risk, the precautionary principle mandates that we consider that risk as real and take all possible steps to limit that risk.”
Taking this into consideration, the question arises as to why the WHO has not yet updated its recommendations accordingly. “The needed studies are hard to do and require significant planning and I myself have submitted multiple proposals to fund work to try answer this question” – says Professor Milton, Affiliate in Cell Biology and Molecular Genetics of the University of Maryland School of Medicine. “But given there are now several reports of the presence of SARS-CoV-2 in respirable aerosols and on exhaust vents indicating potential airborne infection risk, the precautionary principle mandates that we consider that risk as real and take all possible steps to limit that risk. Another factor that might contribute to the WHO’s current recommendation in terms of SARS-CoV-2’s transmissibility is the ability to provide healthcare workers with protection from airborne infection transmission via aerosols is very limited. It is especially so in low- and middle-income countries, but many wealthy countries are not prepared either and are confronting extreme shortages. I think that there is a lot of fear about consequences if workers are told that they cannot be assured of effective engineering controls and proper personal protective equipment” – he adds.
Dr Marc Wathelet, Molecular Biologist, Coronavirus specialist : “Consider what happened in Toronto in 2003 when SARS-CoV was no longer circulating in the community and there were no more cases in the hospital. The strict control measures were lifted and a full month later a new outbreak took place in one community hospital, presumably a fomite that was not cleaned reinitiated transmission, the virus having remained viable for a month.”
Possible recurrence of SARS-CoV-2
Public health emergency preparedness and response to pandemics are of key importance and according to the World Health Organization it is a continuous process of planning, exercising and revising that is translated into national action plans.
A 2006 study estimated the potential mortality of an influenza pandemic, using data from the Spanish flu pandemic of 1918-20. The analysis found that if such a pandemic were to occur today, there would be an estimated 62 million deaths, of which 96% would occur in the developing world, increasing global mortality by 114%. It is interesting to see that the R naught (the measure of how contagious an infectious disease is), for the Spanish flu was 1.8 with a 2.5% mortality rate, while the current pandemic of SARS-CoV has a R naught of 2 with a mortality rate of 4.5%. Therefore, the question arises whether we are well prepared for a pandemic that has a mortality rate greater than that of one of the historically most deadly pandemics, and which could reappear once confinement measures are released. Once confinement is lifted, massive testing abilities are needed to be able to prevent a flare-up. “I think it is quite likely that this virus will become endemic throughout the world, with seasonal variation in its circulation as it is now propagating in the southern hemisphere too” – says Dr Wathelet.
According to the World Health Organization the 2009 influenza pandemic allowed global and national preparedness to be tested in earnest, revealing critical gaps in preparedness, including those in risk assessment, surveillance, health care systems, and the pandemic vaccine’s deployment and acceptance by the public.
However, both Professor Milton and Dr Wathelet agree that the current pandemic planning and approach in fighting global infectious diseases should be reevaluated as they are slow and ineffective, and they also highlight that stockpiles of emergency equipment should be also be maintained.
• A scientist’s opinion : Interview with Prof. Donald Milton about SARS-CoV
• EU Project : COVID-19 Data Portal
• A scientist’s opinion : Interview with Dr. Marc Wathelet about SARS-CoV