It’s been 25+ months since SARS-CoV-2 began its march across the globe and in the time since, multiple variants have arisen that have posed enormous challenges to both medical and public health responses. Most recently, Omicron has once again completely altered the pandemic landscape.
The speed with which Omicron rose to prominence, rapidly overtaking the Delta variant, prompted a series of new questions, like why it is so much more transmissible than previous variants? And how can individuals continue to protect themselves against symptomatic infection, severe illness, and death?
Recently, we asked a group of experts at the University of Vermont (UVM) to answer some of these questions for us.
Introducing the Experts
Benjamin Lee, M.D.
Associate Professor of Pediatrics & Pediatric Infectious Disease Physician
Benjamin Lee, M.D., is an associate professor of pediatrics at the Larner College of Medicine, a pediatric infectious disease physician at the UVM Children’s Hospital, a research project leader for the Translational Global Infectious Diseases Research Center at UVM, and a member of UVM’s Vaccine Testing Center.
Since early 2020, he’s written a number of peer-reviewed articles and been interviewed by local and national media outlets regarding pediatric SARS-CoV-2 cases and the impact of the COVID-19 pandemic on children and schools.
Emily Bruce, Ph.D.
Assistant Professor of Microbiology & Molecular Genetics
Emily Bruce, Ph.D., is a virologist, an assistant professor of microbiology and molecular genetics at Larner, and a member of the Vermont Center for Immunobiology and Infectious Disease. She has been studying RNA viruses for 17 years.
Bruce’s lab specializes in the study of RNA viruses – specifically influenza and SARS- CoV-2. When Bruce started her lab in March 2021, the dominant strain of SARS-CoV-2 was the Alpha variant. A few months later Delta rose to prominence and now, Omicron.
As new variants arise, Bruce and her team work to address urgent questions about infectivity and suitability of various diagnostic tests. In a recent Nature news article, Bruce consulted regarding studies her lab is conducting regarding Omicron’s “hyper-transmissibility.”
Yves Dubief, Ph.D.
Associate Professor of Mechanical Engineering
Yves Dubief, Ph.D., is an expert in fluid dynamics, turbulence theory, complex fluids, and high fidelity simulations and studies the dynamics of non-traditional fluids (more complex than water and air) using supercomputers to achieve the highest degree of accuracy possible for simulations.
In the beginning of 2020, Dubief was on sabbatical leave in Grenoble, France, working at the Laboratoire des Écoulements Géophysiques et Industriels. “When the pandemic hit France, the French government called on all researchers who could to help,” he says. Dubief worked on research regarding sterilization of N95 masks and then, in April 2020, assembled a team of French collaborators to study transmission risk and assess mitigation strategies.
Transmissibility & Infectivity
What do the data tell us about how much more transmissible Omicron is than earlier variants including Alpha and Delta?
The current consensus is that SARS-CoV-2 Omicron variant appears to be about 3-4 times more infectious than the Delta variant, which was itself approximately 50% more infectious than the Alpha variant.
Omicron’s increased immune evasion (compared to Delta) is the factor we have the best evidence for. The increased immune evasion component is clearly part of the picture, since Omicron is better at infecting people who have immunity either through vaccines and/or prior infection. However, as a scientific community, we don’t yet understand the whole picture.
It doesn’t appear that Omicron grows to higher levels in people’s noses, and a very small amount of data suggests that it isn’t any more infectious for a given amount of viral RNA—unlike Delta, which was six times more infectious than Alpha. Omicron spread so rapidly, that I believe there is something about the biology of the virus itself that is different as well. That’s something our lab is starting to look into.
We’ve made such incredible strides in understanding SARS-CoV-2 over the past 25+ months, that it is sometimes hard to remember that it can take years or even decades to understand a particular problem in virology. Moving forward, we have to keep in mind that not every question can be answered in six months of rapid fire experiments.
What can science tell us about why cloth masks and surgical masks were effective for protection against Alpha and Delta but not Omicron?
When comparing N95 and K95 masks, surgical masks, and cloth masks, a lot of the efficacy comes down to fit. Studies have shown that a well-fitted surgical masks has an efficacy over 90%, similar to N95 masks. For a poorly fitted mask, the efficacy drops to 60%.
So, while the material used in surgical masks is highly effective against viruses like the Omicron variant of SARS-CoV-2, the fit is often problematic. For most, a surgical mask leaves gaps over the cheeks (between the edge of the mask and the elastic loop attachment), around the nose, and sometimes under the chin.
Cloth masks can pose similar issues related to fit and there’s a large variety in efficacy depending on the type of fabric itself. Triple-layer cloth masks can be as effective as surgical mask at the expense of breathability.
The bottom line is that fit is as essential as the filtration efficacy of the fabric.
The reason N95 and KN95 masks are recommended is because of their filtration efficacy but also because their nose wires and design of the ear loops or headbands tend to be more substantial and are designed to provide a tighter fit on most faces.
In terms of filtration efficacy, SARS-CoV-2 is roughly 0.1 micrometer (µm) in diameter. Aerosols and droplets containing one or more virus copies range from a few tenths of microns to visible droplets.
There has been a lot of misinformation arguing that masks with pores 100x larger than the diameter of a SARS-CoV-2 virion are not sufficiently protective. This misinformation is rooted in the idea that a mask is a simple kitchen strainer with ~30µm diameter pores. However, KN95s, N95s, and surgical masks are constructed in such a way that aerosols have to make many detours to arrive at the wearer’s face. During these detours, the vast majority of these aerosols get stuck to fibers designed to facilitate adhesion and never make it to a person’s face.
The science of masking is well-established and well-documented. Here is one peer-reviewed study that shows even washed N95 and KN05 masks still offer protection and another peer-reviewed study showing that N95 masks have the smallest pore-diameter and highest density of fibers.
What types of masks do you suggest folks wear at this moment in time? If people can’t afford or can’t find KN95 or N95 masks, what can they do to upgrade their protection using masks they already own?
It depends on the activity.
For healthcare workers who are susceptible to frequent exposure, I highly recommend elastomeric masks. The reason again, comes down to fit.
An elastomeric mask has, by design, a near perfect fit. Hospitals that have invested in such masks have seen no nosocomial infection within their healthcare workers. Elastomeric masks also generate less waste, as the elastomeric part is entirely washable and reusable. In the absence of elastomeric masks, professionally fitted KN95 or N95 should be used.
I must stress, an N95 with a reasonable fit (glasses barely fog, there is no obvious gap forming while breathing), is still a much better fit than most surgical masks.
For most other activities and situations KN95 and N95 masks are strongly recommended. If unaffordable or unavailable, covering a surgical mask with a cloth mask generally solves the fit issues posed by surgical masks. Mask fitters or bracers can also significantly improve the fit of a surgical mask.
Early on in the pandemic, the public was dissuaded from purchasing and wearing KN95 and N95 masks so there would be enough for healthcare professionals. Is this still an issue?
Unlike in early 2020, when mask supply was an issue, there is no longer any reason not to endorse and encourage higher quality masks.
KN95, N95, or KF94 masks are best, but a standard medical-grade procedural/surgical mask is definitely better than cloth facial coverings.
We know that wearing masks inside is necessary to protect against the spread of COVID-19. With the advent of Omicron, should folks consider starting to wear masks outside again as well?
Outside air is always moving and being outside remains very safe.
There is no evidence that I have seen that Omicron has changed this sentiment among the community of aerosol experts.
We may not feel the air moving around us if the flows are less than 4-6 inches per second (10-15 centimeters per second) since this is the lower limit of our skin sensor for air flows. But this air movement combined with large volume makes the outside dilute the concentration of viral aerosols at a much greater rate than any unventilated or poorly ventilated room could.
To be infected outside, a person would have to be standing in the stream of aerosols of a contagious individual for a while. It is not inconceivable that outside infection may occur. However it takes a special set of circumstances (relatively immobile dense crowd, very weak airflows, etc.) and a highly transmissible virus for the outside to become a concern.
Lately, there has been a lot of concern from the public regarding the efficacy of different tests in detecting the presence of the Omicron variant in infected people. Can you address this?
Well, there are multiple things going on when you are talking about a rapid test.
First, you need to understand what a test is measuring. Most rapid tests measure the presence of a viral protein (which is called an ‘antigen’—the thing that is recognized by an antibody). That is different from a polymerase chain reaction (PCR) test, which looks for the presence of viral RNA.
Because of how PCR works, it is more sensitive than most rapid tests because since you can amplify a tiny amount of RNA in a sample using PCR into a much larger amount of RNA (making the presence of the virus in a sample from someone more obvious), but you can’t amplify proteins measured in most rapid tests in the same way. The downside of that sensitivity is that a PCR test takes much longer to run, and sometimes that turn-around time makes it really challenging to use PCR tests to get results quickly enough to act on them.
Second, in order for either test to work, there needs to be enough virus in the place you are swabbing (nose, throat, or nasopharyngeal swab) that the test can ‘see’ it.
Third, where you swab can matter. If the virus is growing in your throat first and you swab your nose you might miss it and vice versa.
There have been anecdotal reports that some people test positive in their throats before their noses for Omicron, but clearly lots of people also test positive in the nose first. It’s also important to remember that rapid tests are not approved for throat swabs in the United States—in other words, the test manufacturers haven’t yet run extensive studies that produce compelling data showing that the tests, which were developed as nasal swabs, work when used in the throat. They might work great, or it might turn out that people who’ve recently eaten a particular food get an inaccurate result—without the data its hard to control for these kinds of real world problems.
Finally, timing of testing is really important. Anecdotally, many people have started to report they are having symptoms for a couple of days before testing positive. This could be because more people have some immunity now (from vaccines or prior infection) and so their body’s immune system is ramping up, and giving them fever/chills before the virus grows to a level a test can see it. But, and this is a big but, we don’t know what is happening to the levels of infectious virus during that time. Rapid tests work great at identifying people with the highest levels of virus, we just don’t know how well the gray area of “just enough virus to transmit” is picked up by various tests, and we don’t know how long you have after a negative rapid test before you might be newly infectious.
Ventilation & Air Purifiers in Indoor Spaces
Are there other precautions people can take inside, aside from wearing properly-fitted high-filtration masks?
Air purifiers have been scientifically shown to achieve great levels of protection against airborne diseases, providing that air purifiers are designed for the volume of the room.
The task of choosing an air purifier can be daunting, therefore don’t hesitate to contact a few aerosol/ventilation experts for advice. Air purifiers should have HEPA filters or MERV 13 filters (or above) for DIY purifiers. UV and air ionization are not recommended. The first, because the virus don’t stay long enough under the UV light in the air purifier to be destroyed. The second, air ionization, may produce ozone which is bad for the health of people in the room.
The quantity to monitor is the clean air delivery rate (CADR) or cubic feet per minute (CFM). For instance, the CADR Corsi-Rosenthal box, a very popular DIY airfilter, has been measured at approximately 600 CFM. This means that a 600-square-foot room with a 10-foot ceiling will receive 10 times its volume in clean air over one hour—the recommended fresh air change per hour (ACH) for HVAC systems to dramatically reduce infections from airborne diseases.
Where should you place an air purifier?
This is a question my team and I are currently studying. The investigation, which aims at finding the optimal placement for a given room with its layout of furniture and people, will take time to come up with the best placements. For now, the general recommendations are to place air purifiers at the center of the room, at least 3 feet from any wall or big furniture and not in the line of airflows leaving the house.
A humidifier is also a good addition to a room, as increased humidity has been shown to reduce the risks of transmission. On warm days, opening all windows is a great idea, if they create enough ventilation.
Children Under Age 5
What is your recommendation for parents of children under 5 years of age who have not yet been able to receive the vaccine? Can children under 5 safely wear KN95 masks or N95 masks if their parents have access to these types of masks?
It is very unfortunate that vaccines for children under 5 are not available yet.
First, I would like to remind everyone that the risk for severe illness due to COVID-19 in this age group is very, very low. It’s important to not lose sight of that observation when assessing risks.
For this age group, the same principles that we know keep adults safe still apply: Avoid crowded indoor places, avoid interactions with sick people (which also means being responsible and staying home or keeping your child home when sick), and wear masks. Of course, the last one is more challenging in this age group.
True N95s were really designed for workplaces and occupational protection, so pediatric sizes are really not available. It may be possible to find KN95 and KF94 masks in smaller sizes suitable for children, but fit will be very important. A poorly fitting KN95 mask may not provide any better protection than a well-fitting surgical mask. In the youngest children who are able to tolerate masks, a high-quality, triple-ply surgical mask in a pediatric size may be the best option, with a cloth facial covering over it as needed to ensure snug fit, if needed.
It is also really important to remember that the United States is unique among countries in even attempting masks in children between 2 and 5 years old. Most countries have accepted that children under 5 shouldn’t be asked to mask, and kids in those locations aren’t doing worse than kids in the U.S.
SARS-CoV-2 will clearly become established as an endemic virus, and we are in the midst of that transition. We’re not there yet, but I think that we have to recognize the reality that all of us will be exposed and infected at some point, the same way we all expect to be infected with flu and other seasonal respiratory viruses at some point over the course of our lifetime.
This is a shift in outlook that can be anxiety-provoking. Yet, with the benefits of vaccination, encouraging treatment options that will hopefully be more widely available in the coming year, and the reduced virulence of Omicron, I firmly believe that we are rapidly nearing a tipping point where moving forward, at both a personal and societal level, we will be able to start incorporating the risk of SARS-CoV-2 into the background of our daily lives rather than having it dominate all aspects of life.
I agree with Dr. Lee’s points above, we are at a transition point here in the United States in how we are able to deal with SARS-CoV-2. And that is due to the enormously powerful tools we now have at our disposal—incredibly effective vaccines developed on an unprecedented timescale; tests that we can use to determine if we are infectious, quickly and in the privacy of our homes; and the availability of masks that are much more effective and more widely available than anything possible in March of 2020.
As a parent of three young children, I am acutely aware that vaccines are still not available to children under 5—which has unfortunately extended the pandemic circumstances for them and their families. However, the failure to provide widespread global access to SARS-CoV-2 vaccines is a problem that is hugely urgent and must be addressed by global efforts. As this pandemic has shown over and over, teamwork matters in combating the threat posed by a virus. Just as we needed to take community action to keep vulnerable friends and family members safe during the last two years, we need to take global action now in order to prevent the kind of widespread viral replication that can allow new viral variants to emerge.
We achieved an extraordinary scientific victory in developing safe vaccines against this virus in less than a year—we need to pair that with an equally ambitious effort to deliver them everywhere they are needed.
Airborne diseases are an invisible threat and safety can be improved with relatively small institutional investments like air purifiers and elastomeric masks.
Appropriately-sized air purifiers add an important layer of protection in settings where people are the most vulnerable—while they eat for example.
In terms of elastomeric masks for healthcare professionals, we just have to look at South Korea, Japan, or the infectious disease hospital in Houston—which has been providing employees with elastomeric masks—to realize that solutions exist to protect us from COVID-19.
With the virus being neurotropic, and its ability to infect multiple organs, we, as a society, ought to better protect healthcare and other essential workers from the risks of long-COVID, and possibly death. The solutions are quite simple: better masking, ventilation and air purification. Arguing against these measures on the basis of their cost makes little sense when considering the incidence of sick days and quarantining among healthcare workers, which in turns stresses the entire healthcare system.