When breezy, wear masks outdoors to prevent coronavirus exposure

As the highly infectious delta variant of the coronavirus continues to spread across the United States, guidelines from the Centers for Disease Control and Prevention recommend even the vaccinated wear masks indoors to prevent exposure and transmission.

However, it is less clear what people should do when outside.

In Physics of Fluids, by AIP Publishing, researchers from the Indian Institute of Technology Bombay found when a person coughs outdoors, wind flowing in the same direction can propagate the virus faster over longer distances than in calm conditions.

"The study is significant in that it points to the increased infection risk that coughing in the same direction as the wind could bring about," co-author Amit Agrawal said. "Based on the results, we recommend wearing masks outdoors, particularly in breezy conditions."

Other guidelines, such as coughing in an elbow or turning the face away while coughing, should be followed to reduce transmission when socializing outdoors.

Most studies model cough flow using puffs of air or a simple pulsating profile. But a real cough is more complicated, exhibiting turbulent flow with prominent vortical structures swirling like mini whirlpools.

To investigate these vortices, the researchers used a large eddy simulation, a numerical model in computational fluid dynamics that simulatesturbulence. They modeled cough jets in breezy conditions and in calm conditions representing a typical indoor environment.

These simulations show even a light breeze of about 5 mph extends effective social distancing by around 20%, from 3-6 feet to 3.6-7.2 feet, depending on cough strength. At 9-11 mph, spreading of the virus increases in distance and duration.

The researchers found the vortices enable bigger droplets to persist in the air longer than has been typically assumed, increasing the time it takes to adequately dilute the viral load in fresh air. As the cough jet evolves and spreads, it interacts with the wind flowing in the same direction, and the bigger infected droplets become trapped in the jet's vortices instead of falling relatively quickly to the ground under gravity.

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With time and without masks, COVID-19 vaccines wane in protection, study finds

In a letter to The New England Journal of Medicine, publishing online September 1, 2021, an interdisciplinary team of physicians and public health experts at University of California San Diego measured the effectiveness of COVID-19 mRNA vaccines among health workers at UC San Diego Health, most notably during the emergence of the highly transmissible delta virus variant and coincident with the end of the state's mask mandate, allowing fully vaccinated persons to forgo face coverings in most places.

The letter's authors report that the effectiveness of both the Pfizer and Moderna mRNA COVID-19 vaccines significantly waned over time. Both vaccines were granted emergency use authorization by the Food and Drug Administration in December 2020, with vaccinations of the UC San Diego Health work force beginning the same month for health care workers with direct, patient-facing duties.

In the letter, the authors note that from March through June 2021 vaccine effectiveness against symptomatic infection was estimated to exceed 90 percent; by July, however, it had fallen to approximately 65 percent.

"The decline in effectiveness is not entirely surprising," said co-senior author Francesca Torriani, MD, professor of clinical medicine in the Division of Infectious Diseases and Global Public Health in the UC San Diego School of Medicine and program director of Infection Prevention and Clinical Epidemiology at UC San Diego Health.

"Clinical trial data suggested decreased effectiveness would occur several months after full vaccination, but our findings indicate that confronted by the delta variant, vaccine effectiveness for mildly symptomatic disease was considerably lower and waned six to eight months after completing vaccination."

UC San Diego Health, with a work force of approximately 19,000, operates a robust SARS-CoV-2 testing program. If an employee reports even one mild symptom of COVID-19 during daily screening or an identified exposure, a test is triggered.

Then and now, UC San Diego Health has maintained rigorous, mandatory masking and transmission mitigation measures throughout its hospitals and clinical facilities. Diagnosed positive cases among health workers have universally been identified as community acquired.

In December 2020, workers at UC San Diego Health, like the population overall, began experiencing a surge of SARS-CoV-2 infections, the virus that causes COVID-19.

The situation improved significantly after UC San Diego Health began to inoculate employees using the Pfizer and Moderna vaccines. By March 2021, 76 percent of workers were fully vaccinated, rising to 83 percent by July 2021.

Concomitant with increased vaccination coverage was a decline between March and June in the number of workers reporting at least one symptom of COVID-19 and a positive PCR test. That number declined to fewer than 30 employees per month.

In July 2021, however, cases among this highly vaccinated population began to rise again, coincident with the emerging dominance of the delta variant in San Diego and the ending of California's masking mandate on June 15. By July, 125 workers had been diagnosed with SARS-CoV-2 and unlike in previous months when approximately 20 percent of these cases involved vaccinated workers, the percentage had risen to 75 percent.

Notably, the vaccines still provide significant protection from severe infection outcomes, such as hospitalization and death. Among the UC San Diego Health employee cases documented, no hospitalizations were reported in vaccinated individuals and only one among unvaccinated persons.

"Unlike what was experienced with other variants, with the delta variant parents are frequently getting infected by their young children, ages 5 to 11," said co-first author Lucy Horton, MD, MPH, an assistant professor of medicine in the Division of Infectious Diseases and director of the UC San Diego Health COVID-19 case investigation and contact tracing team. "Unvaccinated people are seven times more likely to test positive for COVID-19 than those who are fully vaccinated. More importantly, while children rarely need medical attention, unvaccinated adults are 32 times more likely to require hospitalization compared to those who are fully vaccinated."

Vaccine effectiveness was linked to the passage of time. For workers diagnosed in July, those who became fully vaccinated in January and February had higher infection rates than those vaccinated later in March through May. The infection rate among unvaccinated persons has remained consistently higher than for any vaccinated group, although the difference in rates between the two groups has decreased over time.

"The dramatic change in vaccine effectiveness from June to July is likely due to a combination of factors," said co-author Nancy Binkin, MD, MPH, professor of epidemiology in the UC San Diego School of Medicine and Herbert Wertheim School of Public Health and Human Longevity Science. "It's the emergence of the delta variant and waning immunity over time, compounded by the end of broad masking requirements and the resulting greater exposure risk throughout the community."

Co-senior author Shira Abeles, MD, an assistant professor of medicine in the Division of Infectious Diseases who has led the COVID-19 vaccination effort at UC San Diego Health, said the findings underscore the importance of rapidly reinstating key interventions, such as indoor masking and intensive testing strategies, plus continuing efforts to boost vaccination rates.

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Masks, ventilation stop COVID spread better than social distancing, study shows

 A new study from the University of Central Florida suggests that masks and a good ventilation system are more important than social distancing for reducing the airborne spread of COVID-19 in classrooms.

The research, published recently in the journal Physics of Fluids, comes at a critical time when schools and universities are considering returning to more in-person classes in the fall.

"The research is important as it provides guidance on how we are understanding safety in indoor environments," says Michael Kinzel, an assistant professor in UCF's Department of Mechanical and Aerospace Engineering and study co-author.

"The study finds that aerosol transmission routes do not display a need for six feet social distancing when masks are mandated," he says. "These results highlight that with masks, transmission probability does not decrease with increased physical distancing, which emphasizes how mask mandates may be key to increasing capacity in schools and other places."

In the study, the researchers created a computer model of a classroom with students and a teacher, then modeled airflow and disease transmission, and calculated airborne-driven transmission risk.

The classroom model was 709 square feet with 9-foot-tall ceilings, similar to a smaller-size, university classroom, Kinzel says. The model had masked students -- any one of whom could be infected -- and a masked teacher at the front of the classroom.

The researchers examined the classroom using two scenarios -- a ventilated classroom and an unventilated one -- and using two models, Wells-Riley and Computational Fluid Dynamics. Wells-Riley is commonly used to assess indoor transmission probability and Computational Fluid Dynamics is often used to understand the aerodynamics of cars, aircraft and the underwater movement of submarines.

Masks were shown to be beneficial by preventing direct exposure of aerosols, as the masks provide a weak puff of warm air that causes aerosols to move vertically, thus preventing them from reaching adjacent students, Kinzel says.

Additionally, a ventilation system in combination with a good air filter reduced the infection risk by 40 to 50% compared to a classroom with no ventilation. This is because the ventilation system creates a steady current of air flow that circulates many of the aerosols into a filter that removes a portion of the aerosols compared to the no-ventilation scenario where the aerosols congregate above the people in the room.

These results corroborate recent guidelines from the U.S. Centers for Disease Control and Prevention that recommend reducing social distancing in elementary schools from six to three feet when mask use is universal, Kinzel says.

"If we compare infection probabilities when wearing masks, three feet of social distancing did not indicate an increase in infection probability with respect to six feet, which may provide evidence for schools and other businesses to safely operate through the rest of the pandemic," Kinzel says.

"The results suggest exactly what the CDC is doing, that ventilation systems and mask usage are most important for preventing transmission and that social distancing would be the first thing to relax," the researcher says.

When comparing the two models, the researchers found that Wells-Riley and Computational Fluid Dynamics generated similar results, especially in the non-ventilated scenario, but that Wells-Riley underpredicted infection probability by about 29 percent in the ventilated scenario.

As a result, they recommend some of the additional complex effects captured in Computational Fluid Dynamics be applied to Wells-Riley to develop a more complete understanding of risk of infection in a space, says Aaron Foster, a doctoral student in UCF's Department of Mechanical and Aerospace Engineering and the study's lead author.

"While the detailed Computational Fluid Dynamics results provided new insights into the risk variation and distance relationships, they also validated the more commonly used Wells-Riley models as capturing the majority of the benefit of ventilation with reasonable accuracy," Foster says. "This is important since these are publicly available tools that anyone can use to reduce risk."

The research is part of a larger overall effort to control airborne disease transmission and better understand factors related to being a super-spreader. The researchers are also testing the effects of masks on aerosol and droplet transmission distance. The work is funded in part by the National Science Foundation.

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Masks don't impair lung function during physical activity, study finds

 Wearing a facemask helps limit the spread of COVID-19 by reducing respiratory droplets and aerosols spewed into the air when people breathe, talk, laugh, sneeze or cough. But the physical barrier created by masks has prompted concerns that they might impair the cardiopulmonary system by making it harder to breathe, by altering the flow of inhaled oxygen and exhaled carbon dioxide and by increasing dyspnea -- a medical term that describe shortness of breath or difficulty breathing, especially during physical activity.

In a new study, published November 16, 2020 in the Annals of the American Thoracic Society, a team of American and Canadian researchers concluded that while sensations of dyspnea might increase, there is little empirical evidence that wearing a facemask significantly diminishes lung function, even when worn during heavy exercise.

"There might be a perceived greater effort with activity, but the effects of wearing a mask on the work of breathing, on gases like oxygen and CO2 in blood or other physiological parameters are small, often too small to be detected," said the study's first author Susan Hopkins, MD, PhD, professor of medicine and radiology at University of California San Diego School of Medicine.

"There's also no evidence to support any differences by sex or age in physiological responses to exercise while wearing a facemask," added Hopkins, who specializes in exercise physiology and the study of lungs under stress.

The single exception, the authors note, may be persons with severe cardiopulmonary disease in which any added resistance to breathing or minor changes in blood gases could prompt dyspnea great enough to affect exercise capacity.

"In such cases, these individuals might feel too uncomfortable to exercise, and that should be discussed with their doctor," Hopkins said. "However, the fact that these individuals are at great risk should they contract COVID-19 must also be considered"

The researchers came to their conclusions following a review of all known scientific literature published that examined the effects of various facemasks and respiratory loading devices on physiological and perceptual responses to physical activity. These studies assessed multiple factors, such as work of breathing (the quantified energy expended to inhale and exhale), arterial blood gases, effects on muscle blood flow and fatigue, cardiac function and flow of blood to the brain.

For healthy persons, the effects of wearing a mask on these physiological markers were minimal, no matter what type of mask was worn or the degree of exercise. The authors also said age played no significant influencing role among adults. Gender differences were deemed inconsequential.

"Wearing a facemask can be uncomfortable," said Hopkins. "There can be tiny increases in breathing resistance. You may re-inhale warmer, slightly enriched CO2 air. And if you're exercising, the mask can cause your face to become hot and sweaty.

"But these are sensory perceptions. They do not impact cardiopulmonary function in healthy people. So while dyspnea might be increased with a mask, you have to weigh that against the reduced risk of contracting COVID-19, knowing that the physiology is essentially unchanged."

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Large, delayed outbreaks of endemic diseases possible following COVID-19 controls

 

Illustration, people wearing masks.

Measures to reduce the spread of COVID-19 through non-pharmaceutical interventions (NPIs) such as mask wearing and social distancing are a key tool in combatting the impact of the ongoing coronavirus pandemic. These actions also have greatly reduced incidence of many other diseases, including influenza and respiratory syncytial virus (RSV).

Current reductions in these common respiratory infections, however, may merely postpone the incidence of future outbreaks, according to a study by Princeton University researchers published Nov. 9 in the Proceedings of the National Academy of Sciences.

"Declines in case numbers of several respiratory pathogens have been observed recently in many global locations," said first author Rachel Baker, an associate research scholar at the High Meadows Environmental Institute (HMEI) at Princeton University.

"While this reduction in cases could be interpreted as a positive side effect of COVID-19 prevention, the reality is much more complex," Baker said. "Our results suggest that susceptibility to these other diseases, such as RSV and flu, could increase while NPIs are in place, resulting in large outbreaks when they begin circulating again."

Baker and her co-authors found that NPIs could lead to a future uptick in RSV -- an endemic viral infection in the United States and a leading cause of lower respiratory-tract infections in young infants -- but that the same effect was not as pronounced for influenza.

"Although the detailed trajectory of both RSV and influenza in the coming years will be complex, there are clear and overarching trends that emerge when one focuses on some essential effects of NPIs and seasonality on disease dynamics," said co-author Gabriel Vecchi, Princeton professor of geosciences and the High Meadows Environmental Institute.

The researchers used an epidemiological model based on historic RSV data and observations of the recent decline in RSV cases to examine the possible impact of COVID-19 NPIs on future RSV outbreaks in the United States and Mexico.

They found that even relatively short periods of NPI measures could lead to large future RSV outbreaks. These outbreaks were often delayed following the end of the NPI period, with peak cases projected to occur in many locations in winter 2021-22. "It is very important to prepare for this possible future outbreak risk and to pay attention to the full gamut of infections impacted by COVID-19 NPIs," Baker said.

The authors also considered the implications of COVID-19 NPIs for seasonal influenza outbreaks and found results qualitatively similar to RSV. The dynamics of influenza are much harder to project due to viral evolution, however, which drives uncertainty over future circulating strains and the efficacy of available vaccines.

"For influenza, vaccines could make a big difference," Baker said. "In addition, the impact of NPIs on influenza evolution is unclear but potentially very important."

"The decrease in cases of influenza and RSV -- as well as the possible future increase we project -- is arguably the broadest global impact of NPIs across a variety of human diseases that we've seen," said co-author Bryan Grenfell, the Kathryn Briger and Sarah Fenton Professor of Ecology and Evolutionary Biology and Public Affairs, who is associated faculty in HMEI.

"NPIs could have unintended longer-term impacts on the dynamics of other diseases that are similar to the impact on susceptibility we projected for RSV," he said.

A similar effect of pandemic-related NPIs on other pathogens was observed following the 1918 influenza pandemic. Historic measles data from London show a shift from annual cycles to biennial outbreaks following a period of control measures implemented at that time.

Co-author C. Jessica Metcalf, associate professor of ecology and evolutionary biology and public affairs and an associated faculty member in HMEI, said that directly evaluating the associated risks of NPIs by developing and deploying tools such as serology that would better measure susceptibility is an important public health and policy direction. "The future repercussions of NPIs revealed by this paper hinge on how these measures change the landscape of immunity and susceptibility," Metcalf said.

Additional authors on the paper include Wenchang Yang, an associate research scholar in geosciences, and Sang Woo Park, a Ph.D. candidate in ecology and evolutionary biology.

Many of the authors are affiliated with the Climate Change and Infectious Disease initiative funded by HMEI and the Princeton Institute for International and Regional Studies (PIIRS). The current study built on work by the same team published in December 2019 that examined how climate conditions affect RSV outbreaks in the US and Mexico. Another study by the team, published earlier this year, evaluated the impact of the climate and susceptibility on the trajectory of the COVID-19 pandemic.

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Effectiveness of cloth masks depends on type of covering

 Months into the COVID-19 pandemic, wearing a mask while out in public has become the recommended practice. However, many still question the effectiveness of this.

To allay these doubts, Padmanabha Prasanna Simha, from the Indian Space Research Organisation, and Prasanna Simha Mohan Rao, from the Sri Jayadeva Institute of Cardiovascular Sciences and Research, experimentally visualized the flow fields of coughs under various common mouth covering scenarios. They present their findings in the journal Physics of Fluids, from AIP Publishing.

"If a person can reduce the extent of how much they contaminate the environment by mitigating the spread, it's a far better situation for other healthy individuals who may enter places that have such contaminated areas," Simha said.

Density and temperature are intricately related, and coughs tend to be warmer than their surrounding area. Tapping into this connection, Simha and Rao utilized a technique called schlieren imaging, which visualizes changes in density, to capture pictures of voluntary coughs from five test subjects. By tracking the motion of a cough over successive images, the team estimated velocity and spread of the expelled droplets.

Unsurprisingly, they found N95 masks to be the most effective at reducing the horizontal spread of a cough. The N95 masks reduced a cough's initial velocity by up to a factor of 10 and limit its spread to between 0.1 and 0.25 meters.

An uncovered cough, in contrast, can travel up to 3 meters, but even a simple disposable mask can bring this all the way down to 0.5 meters.

"Even if a mask does not filter out all the particles, if we can prevent clouds of such particles from traveling very far, it's better than not doing anything," said Simha. "In situations where sophisticated masks are not available, any mask is better than no mask at all for the general public in slowing the spread of infection."

Some of the other comparisons, however, were striking.

For example, using an elbow to cover up a cough is typically considered a good alternative in a pinch, which is contradictory to what the pair found. Unless covered by a sleeve, a bare arm cannot form the proper seal against the nose necessary to obstruct airflow. A cough is then able to leak through any openings and propagate in many directions.

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Inexpensive, accessible device provides visual proof that masks block droplets

 

  Duke physician Eric Westman was one of the first champions of masking as a means to curtail the spread of coronavirus, working with a local non-profit to provide free masks to at-risk and under-served populations in the greater Durham community.

But he needed to know whether the virus-blocking claims mask suppliers made were true, to assure he wasn't providing ineffective masks that spread viruses along with false security. So he turned to colleagues in the Duke Department of Physics: Could someone test various masks for him?

Martin Fischer, Ph.D., a chemist and physicist, stepped up. As director of the Advanced Light Imaging and Spectroscopy facility, he normally focuses on exploring new optical contrast mechanisms for molecular imaging, but for this task, he MacGyvered a relatively inexpensive apparatus from common lab materials that can easily be purchased online. The setup consisted of a box, a laser, a lens, and a cell phone camera.

In a proof-of-concept study appearing online Aug. 7 in the journal Science Advances, Fischer, Westman and colleagues report that the simple, low-cost technique provided visual proof that face masks are effective in reducing droplet emissions during normal wear.

"We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing," Fischer said. "We could also see that some face coverings performed much better than others in blocking expelled particles."

Notably, the researchers report, the best face coverings were N95 masks without valves -- the hospital-grade coverings that are used by front-line health care workers. Surgical or polypropylene masks also performed well.

But hand-made cotton face coverings provided good coverage, eliminating a substantial amount of the spray from normal speech.

On the other hand, bandanas and neck fleeces such as balaclavas didn't block the droplets much at all.

"This was just a demonstration -- more work is required to investigate variations in masks, speakers, and how people wear them -- but it demonstrates that this sort of test could easily be conducted by businesses and others that are providing masks to their employees or patrons," Fischer said.

"Wearing a mask is a simple and easy way to reduce the spread of COVID-19," Westman said. "About half of infections are from people who don't show symptoms, and often don't know they're infected. They can unknowingly spread the virus when the cough, sneeze and just talk.

"If everyone wore a mask, we could stop up to 99% of these droplets before they reach someone else," Westman said. "In the absence of a vaccine or antiviral medicine, it's the one proven way to protect others as well as yourself."

Westman and Fischer said it's important that businesses supplying masks to the public and employees have good information about the products they're providing to assure the best protection possible.

"We wanted to develop a simple, low-cost method that we could share with others in the community to encourage the testing of materials, masks prototypes and fittings," Fischer said. "The parts for the test apparatus are accessible and easy to assemble, and we've shown that they can provide helpful information about the effectiveness of masking."

Westman said he put the information immediately to use: "We were trying to make a decision on what type of face covering to purchase in volume, and little information was available on these new materials that were being used."

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