The continued increase in COVID-19 infection around the world has led scientists from many different fields, including biomedicine, epidemiology, virology, fluid dynamics, aerosol physics, and public policy, to study the dynamics of airborne transmission.
Writing in Physics of Fluids, researchers from Johns Hopkins University and the University of Mississippi used a model to understand airborne transmission that is designed to be accessible to a wide range of people. Employing basic concepts of fluid dynamics and the known factors in airborne transmission
of diseases, the researchers propose the Contagion Airborne Transmission (CAT) inequality model. While not all factors in the CAT inequality model may be known, it can still be used to assess relative risks, since situational risk is proportional to exposure time.
The researchers write: “Given this complexity of phenomenology and the many factors involved, it is not surprising that even after more than eight months of the world dealing with the COVID-19 pandemic, there are fundamental questions that continue to confound scientists, policy makers, and the members of the public at large. These include the following questions: What factors have enabled the SARS-CoV-2 to spread so much faster and more extensively than other similar viruses in the recent past? Why is the rate of infection so different in different regions/ countries of the world? How much lower is the likelihood of transmission in an outdoor environment compared to an indoor environment? How do policies and societal behaviour such as compliance with mask wearing affect the rate of transmission? Finally, how does the transmission risk reduce with distance between the host and the susceptible?
Using the model, the researchers determined protection from transmission increases with physical distancing in an approximately linear proportion.
“If you double your distance, you generally double your protection,” said author Rajat Mittal. “This kind of scaling or rule can help inform policy.” The scientists also found even simple cloth masks provide significant protection and could reduce the spread of COVID- 19. “We also show that any physical activity that increases the breathing rate and volume of people will increase the risk of transmission,” said Mittal. “These findings have important implications for the reopening of schools, gyms, or malls.”
The CAT inequality model is inspired by the Drake equation in astrobiology and develops a similar factorization based on the idea that airborne transmission occurs if a susceptible person inhales a viral dose that exceeds the minimum infectious dose.
The model includes variables that can be added at each of the three stages ofairborne transmission: the generation, expulsion, and aerosolization of the viruscontaining droplets from the mouth and nose of an infected host; the dispersion and transport via ambient air currents; and the inhalation of droplets or aerosols and the deposition of the virus in the respiratory mucosa in a susceptible person.
The researchers hope to look more closely at face mask efficacy and the transmission details in high-density outdoor spaces. Beyond COVID-19, this model based on the CAT inequality could apply to the airborne transmission of other respiratory infections, such as flu, tuberculosis, and measles.
- doi: https://aip.scitation.org/
doi/10.1063/5.0025476
Global tracker of COVID-19 vaccine development
Professor Nicole Basta of Canada’s McGill University and her team have created an interactive online COVID-19 vaccine tracker for more than 50 vaccines currently in development. The tracker provides real-time updates on development progress.
“Our goal with the vaccine tracker is to help the public find and access reliable information about COVID-19 vaccines, improve understanding about the vaccine testing process, and manage expectations about when a vaccine may be available,” says Prof. Basta, an associate professor in the Department of Epidemiology, Biostatistics and Occupational Health.
The vaccine tracker features weekly, real-time updates to monitor progress on each of the more than 50 vaccines currently in human trials; behind the scenes, the team is developing and updating a comprehensive database detailing the characteristics of the vaccines in development around the world. Each vaccine candidate has its own card, with an infographic showing whether the vaccine is in phase 1, 2 or 3 of clinical trials or approved, and information about the developers, countries involved, and vaccine type, such as RNAbased, protein subunit, or inactivated virus.
A colour-coded map also updates the number of vaccine candidates, registered vaccine trials, and highest trial stage for each country.
Greater transparency about the strengths and limitations of vaccine candidates are vital to building rather than undermining public trust in vaccines, says Prof. Basta.
COVID-19 Vaccine Tracker https://covid19.trackvaccines.org/
Study estimates exposure to air pollution increases COVID-19 deaths by 15% worldwide
Long-term exposure to air pollution has been linked to an increased risk of dying from COVID-19 and, for the first time, a study has estimated the proportion of deaths from the coronavirus that could be attributed to the exacerbating effects of air pollution for every country in the world.
The study, published in Cardiovascular Research, estimated that about 15% of deaths worldwide from COVID-19 could be attributed to long-term exposure to air pollution. In Europe the proportion was about 19%, in North America it was 17%, and in East Asia about 27%.
In their paper, the researchers write that these proportions are an estimate of “the fraction of COVID-19 deaths that could be avoided if the population were exposed to lower counterfactual air pollution levels without fossil fuel-related and other anthropogenic emissions”.
They add that this “attributable fraction does not imply a direct cause-effect relationship between air pollution and COVID- 19 mortality (although it is possible). Instead it refers to relationships between two, direct and indirect, i.e. by aggravating co-morbidities that could lead to fatal health outcomes of the virus infection”.
The researchers used epidemiological data from previous US and Chinese studies of air pollution and COVID-19 and the SARS outbreak in 2003, supported by additional data from Italy. They combined this with satellite data showing global exposure to polluting fine particles known as ‘particulate matter’ that are less than or equal to 2.5 microns (PM2.5) in diameter information on atmospheric conditions and groundbased pollution monitoring networks, to create a model to calculate the fraction of coronavirus deaths that could be attributable to long-term exposure to PM2.5. The results are based on epidemiological data collected up to the third week in June 2020 and the researchers say a comprehensive evaluation will need to follow after the pandemic has subsided.
Estimates for individual countries show, for example, that air pollution contributed to 29% of coronavirus deaths in the Czech Republic, 27% in China, 26% in Germany, 22% in Switzerland, 21% in Belgium, 19% in The Netherlands, 18% in France, 16% in Sweden, 15% in Italy, 14% in the UK, 12% in Brazil, 11% in Portugal, 8% in the Republic of Ireland, 6% in Israel, 3% in Australia and just 1% in New Zealand.
Prof. Jos Lelieveld said: “Since the numbers of deaths from COVID-19 are increasing all the time, it’s not possible to give exact or final numbers of COVID-19 deaths per country that can be attributed to air pollution. However, as an example, in the UK there have been over 44,000 coronavirus deaths and we estimate that the fraction attributable to air pollution is 14%, meaning that more than 6,100 deaths could be attributed to air pollution. In the USA, more than 220,000 COVID deaths with a fraction of 18% yields about 40,000 deaths attributable to air pollution.”
Prof. Münzel said: “When people inhale polluted air, the very small polluting particles, the PM2.5, migrate from the lungs to the blood and blood vessels, causing inflammation and severe oxidative stress, which is an imbalance between free radicals and oxidants in the body that normally repair damage to cells. This causes damage to the inner lining of arteries, the endothelium, and leads to the narrowing and stiffening of the arteries. The COVID-19 virus also enters the body via the lungs, causing similar damage to blood vessels, and it is now considered to be an endothelial disease.
“If both long-term exposure to air pollution and infection with the COVID-19 virus come together then we have an additive adverse effect on health, particularly with respect to the heart and blood vessels,which leads to greater vulnerability and less resilience to COVID-19. If you already have heart disease, then air pollution and coronavirus infection will cause trouble that can lead to heart attacks, heart failure and stroke.”
Referring to previous work that suggests that the fine particulates in air pollution may prolong the atmospheric lifetime of infectious viruses and help them to infect more people, Prof. Lelieveld said: “It’s likely that particulate matter plays a role in ‘super-spreading events’ by favouring transmission.”
Prof. Münzel added: “Particulate matter seems to increase the activity of a receptor on cell surfaces, called ACE-2, thatis known to be involved in the way COVID- 19 infects cells. So we have a ‘double hit’: air pollution damages the lungs and increases the activity of ACE-2, which in turn leads to enhanced uptake of the virus by the lungs and probably by the blood vessels and the heart.”
In their paper, the authors conclude: “Our results suggest the potential for substantial benefits from reducing air pollution exposure, even at relatively low PM2.5 levels. . . A lesson from our environmental perspective of the COVID-19 pandemic is that the quest for effective policies to reduce anthropogenic emissions, which cause both air pollution and climate change, needs to be accelerated.
The pandemic ends with the vaccination of the population or with herd immunity through extensive infection of the population. However, there are no vaccines against poor air quality and climate change. The remedy is to mitigate emissions. The transition to a green economy with clean, renewable energy sources will further both environmental and public health locally through improved air quality and globally by limiting climate change.”
The study is also the first of its kind to distinguish between fossil fuel-related and other human-made sources of air pollution.
Multi-organ impact of COVID-19 revealed in new study
Initial findings from a study looking at the longer-term impact of COVID-19 has found that a large proportion COVID- 19 patients discharged from hospital were still experiencing symptoms of breathlessness, fatigue, anxiety and depression two to three months after contracting the virus.
The University of Oxford scientists carrying out the C-MORE study have also detected abnormalities on MRI in multiple organs and believe that persistent or chronic inflammation may be an underlying factor for these changes among COVID-19 survivors.
The study, whose initial findings were published online as a pre-print on MedRxiv, is being led by researchers from the university’s Radcliffe Department of Medicine and is supported by the NIHR Oxford Biomedical Research Centre (BRC) and the NIHR Oxford Health BRC, as well as the BHF Oxford Centre for Research Excellence and Wellcome Trust. The C-MORE study is also part of the national PHOSP-COVID platform, led by the University of Leicester, which is investigating the long-term effects of COVID-19 on hospitalised patients.
The study took 58 patients with moderate to severe laboratory-confirmed COVID- 19, who had been admitted for treatment at the Oxford University Hospitals (OUH) NHS Foundation Trust between March and May 2020. They also recruited 30 uninfected controls from the community, group-matched for age, sex, body mass index and risk factors such as smoking, diabetes and hypertension.
The participants underwent magnetic resonance imaging (MRI) of their brain, lungs, heart, liver and kidneys; spirometry to test their lung function; a six-minute walk test; cardiopulmonary exercise test (CPET), as well as assessments of their quality of life, cognitive and mental health.
The C-MORE study found that two to three months after the onset of the disease, 64% of patients experienced persistent breathlessness and 55% complained of significant fatigue.
On MRI, tissue signal abnormalities were seen in the lungs of 60% of the COVID-19 patients, in the kidneys of 29%, in the hearts of 26%, and the livers of 10%. Organ abnormalities were seen even in patients who had not been critically ill when admitted.
MRI also detected tissue changes in parts of the brain, and patients demonstrated impaired cognitive performance. Their ability to sustain exercise was also significantly reduced, although this was due to a combination of fatigue and lung abnormalities.
The study also found that patients were more likely to report symptoms of anxiety and depression, and a significant impairment in their quality of life compared to the controls.
Dr Betty Raman, who is leading the CMORE study along with Professor Stefan Neubauer, said: “Our study assessed patients recovering from COVID-19 following hospitalisation, two to three months from disease onset. Whilst we have found abnormalities in multiple organs, it is difficult to know how much of this was pre-existing and how much has been caused by COVID-19.
“However, it is interesting to see that the abnormalities detected on MRI and exercise capacity in patients strongly correlated with serum markers of inflammation. This suggests a potential link between chronic inflammation and ongoing organ damage among survivors.”
Dr Raman, a Clinical Research Fellow at the Radcliffe Department of Medicine, added: “These findings underscore the need to further explore the physiological processes associated with COVID-19 and to develop a holistic, integrated model of clinical care for our patients after they have been discharged from hospital.
