Is the coronavirus transmitted by air and should everyone wear masks

Ed Yong

Popularizer of science, author of the book “How microbes rule us».

The coronavirus epidemic continues and many are now panicking over things they never thought about before. Can I go outside? What if a person is walking towards, and the wind is blowing from his side? What if you need to wait out the red light, and someone is already at the intersection? What if on a run you see another runner approaching and the track is narrow? Everyday little things suddenly began to demand deliberate behavior.

This is largely due to the fact that data on the coronavirus is constantly changing. Until recently, it was officially believed that the virus is transmitted only through close contact with an infected person or objects. But some time ago, doubts arose. News began to appearA choir decided to go ahead with rehearsal. Now dozens of members have COVID-19 and two are deadindicating that the coronavirus is likely to be airborne as well. Let's try to figure it out.

Is the coronavirus airborne

The confusion has arisen due to the fact that in the scientific sense, "airborne" is not the same as simply "airborne."

If a person has contracted a virus that causes respiratory tract infections, they emit viral particles when they speak, breathe, coughs and sneezes. These particles are trapped in balls of mucus, saliva and water. The shell of large balls does not have time to evaporate, and they settle on the surrounding surfaces. They are traditionally calledCOVID-19 persistence: modes of transmission and precautions respiratory drops. For smaller balls, the shell evaporates faster than they fall. As a result, the "dried up" particles remain in the air and float away further. They are called airborne droplets of infectious particles, or aerosol.

When scientists say the virus is “airborne,” like measles and chickenpox, they mean it travels as a suspension of infectious particles. And when WHO declaredModes of transmission of virus causing COVID ‑ 19: implications for IPC precaution recommendations.that the new type of coronavirus "is not transmitted by airborne droplets," she meant that he was the first the queue spreads due to respiratory drops falling directly on a person's face or on others items.

However, according to Don Milton, who studies the spread of viruses in the air, the traditional separation into short-range droplets and long-range aerosols is based on outdated data. For example, scientists from the Massachusetts Institute of Technology have proven that exhaling, sneezing and coughing createTurbulent Gas Clouds and Respiratory Pathogen Emissions. Potential Implications for Reducing Transmission of COVID-19 rotating, fast moving clouds, consisting of both respiratory droplets and aerosols. And they spread much further than previously thought.

In a common sense, we can say that the coronavirus is airborne.

Therefore, now we should be concerned with other issues. How far do the particles travel? Are they stable and focused enough at the end of their journey to infect someone?

Several studies have provided preliminary answers to these questions. One team of scientists injected fluids containing the virus into a rotating cylinder to create a cloud of infectious particles. They foundAerosol and Surface Stability of SARS ‑ CoV ‑ 2 as Compared with SARS ‑ CoV ‑ 1that inside this cloud the virus remained stable for several hours. However, this does not mean that everything happens the same with the air on the street.

The researchers themselves notedHow Long Will Coronavirus Live on Surfaces or in the Air Around You?that the conditions of the experiment are an artificial environment, and its result does not reflect what happens when you just walk down the street. “These conditions, rather, are close to invasive medical procedures like intubation (insertion of a tube for mechanical ventilation of the lungs - Approx. ed.), which are at risk of aerolizing the virus, ”explains Saskia Popescu, an epidemiologist at George Mason University in Virginia.

Other researchers from the University of Nebraska foundTransmission Potential of SARS ‑ CoV ‑ 2 in Viral Shedding Observed at the University of Nebraska Medical Center traces of coronavirus RNA (genetic material of the virus) in the wards where the sick lived. Moreover, the majority had mild symptoms. The viral RNA was present not only on such obvious objects as the bed and the toilet, but also in hard-to-reach places: on the ventilation grills, the outdoor window sill, on the floor under the bed. Moreover, RNA particles were found even outside the doorstep. However, this is not yet a reason for panic.

Finding viral RNA in a sick room is like finding a fingerprint at a crime scene.

As of April 13, the Nebraska team has failed to detect a live pathogenic virus in air samples. If found, it will mean that even people with mild symptoms can release coronavirus particles into the air, and he is able to move at least through the hospital ward. The latter assumption is supported by several other studies (the firstAerodynamic Characteristics and RNA Concentration of SARS ‑ CoV ‑ 2 Aerosol in Wuhan Hospitals during COVID ‑ 19 Outbreak, second Air, Surface Environmental, and Personal Protective Equipment Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS ‑ CoV ‑ 2) From a Symptomatic Patient).

But even this does not guarantee that there is a threat everywhere in the air. Do these viral particles have enough concentration to infect someone else in the same room? How many particles do you need for this? How far does the virus travel outside and in other rooms? Did such movements affect pandemic development?

There are no answers to these questions yet. To get them, says epidemiologist Bill Hanage, animals would have to be exposed to varying amounts of viruses transmitted by airborne droplets, see if they get infected, and compare this with the virus content in places with infected people. “This kind of work will take years, no one will find the answer right now,” says the scientist.

Is it safe to go outside

All the experts I spoke with while writing this article agree that it is mostly safe. Moreover, walking is essential for maintaining mental health. Distance and ventilation are important to protect against infection; both are sufficient outdoors. The risk arises from the fact that many people gather close to each other, and not because the air is filled with some kind of viral fumes.

“People imagine whole clouds of viruses wandering through the streets and flying after them, but risk of infection higher when you're closer to the source, ”explains Linsey Marr of Virginia Tech, who studies airborne infections. “Going outside is a great idea, unless you’re in a crowded park.”

In February, scientists from Wuhan took air samples from various public places, and it turned outAerodynamic Characteristics and RNA Concentration of SARS ‑ CoV ‑ 2 Aerosol in
Wuhan Hospitals during COVID-19 Outbreakthat the virus was either absent or present at an incredibly low concentration. There were only two exceptions: in front of the supermarket and next to the hospital. Even there, there were less than a dozen viral particles for every cubic meter of air. It is not yet known how many SARS-CoV-2 particles are needed for a person to become infected, but there are calculations for the first coronavirus (SARS) of 2003Development of a dose-response model for SARS coronavirus, and this number is many times greater than the number of particles found by researchers in Wuhan.

“I think we will find out that SARS ‑ CoV ‑ 2 is not particularly stable in the environment, like many other viruses,” said microbiologist Joshua Santarpia of the University of Nebraska. "You shouldn't get into large groups outside, but it's still a great idea to go for a walk or sit on the front veranda on a sunny day."

In order not to dwell on possible risks when you go for a walk, Lincy Marr advises the following. Imagine that all passers-by are smoking, and choose your road so as to inhale as little smoke as possible. When someone passes by, and there is nowhere to move, you can hold your breath. “I do it myself,” says Marr. “I don’t know if it helps, but in theory it can. It's like walking through a cloud of cigarette smoke. "

There is no consensus on the rules of conduct in the premises. Take at least the shops - one of the last strongholds of social life. Someone is more concerned not with the air inside, but with surfaces that many people touch, and after leaving, they must treat their hands with an antiseptic. Someone tries to go to supermarkets when there are fewer people. They also recommend staying as far away from other shoppers as possible, and shopkeepers getting better ventilation.

Of course, there are other common areas such as staircases and elevators. The latter are the most dangerous, because ventilation in them is limited. Use common sense: if you hear neighbors coming out, wait a bit before going out yourself. If you have shared ventilation with them, don't panic or block the vents. Ventilate the apartment once or twice a day.

Should everyone wear masks

This is the most controversial issue. So far, everyone agrees only that this is a must for medical workers. There is no consensus about the rest. For several months, WHO, the US Centers for Disease Control and Prevention, and most health officials saidCoronavirus disease (COVID-19) advice for the public: When and how to use masksthat the mask should only be worn if you are sick or caring for a sick person. They also recognized that there is an acute shortage of masks for medical staff.

In April, the tension reached a critical point. Scientists and journalists began encouraging Western countries to use masks extensively, following the example of East Asia. Masks have become mandatory for all visitorsAustria to make basic face masks compulsory in supermarkets supermarkets in Austria and all leavingCzechs get to work making masks after government decree from home in the Czech Republic and Slovakia. In the US, the Centers for Disease Control and Prevention changed their guidelinesRecommendation Regarding the Use of Cloth Face Coverings, Especially in Areas of Significant Community-Based Transmission, advising covering your face in public.

If the virus is airborne, it seems obvious that a mask will stop it. But the data of scientists is very contradictory, especially on surgical masks that do not fit tightly to the face.

Some studies have found that masks reduceEffectiveness of surgical masks against influenza bioaerosols. the risk of flu-like infectionsFace Mask Use and Control of Respiratory Virus Transmission in Households., slow downThe role of facemasks and hand hygiene in the prevention of influenza transmission in households: results from a cluster randomized trial; Berlin, Germany, 2009-2011. transmission of influenza at home and even reducePhysical interventions to interrupt or reduce the spread of respiratory viruses: systematic review spread of the SARS virus, especially when combined with hand washing and wearing gloves. Other studies were more controversial, findingFindings from a household randomized controlled trial of hand washing and face masks to reduce influenza transmission in Bangkok, Thailand.that masks at allEffectiveness of personal protective measures in reducing pandemic influenza transmission: A systematic review and meta ‑ analysis do not bring good, bring littleFace Mask Use and Control of Respiratory Virus Transmission in Households benefit or helpMask use, hand hygiene, and seasonal influenza-like illness among young adults: A randomized intervention trial only if other measures are taken.

However, there is one good reason for using masks. Even if they cannot catch the virus from the environment, they will not let the virus coming from you out. According to the latest dataRespiratory virus shedding in exhaled breath and efficacy of face masksPeople infected with milder forms of coronaviruses emit fewer viral particles when wearing surgical masks.

“I was pretty dismissive of the masks, but I looked at them from the wrong side,” says Bill Hanage. "They are not worn in order not to get infected, but in order not to infect others." In the situation with SARS ‑ CoV ‑ 2, this is especially important because it is spread even by those who do not yet have symptoms.

Since people carry the infection before symptoms appear, then everyone should wear masks in public.

And yet they are not a panacea. China advocated the wearing of masks from the very beginning, but still could not contain the spread of the infection. In Singapore, masks were used primarily by medical workers, but the increase in infections was reduced there. Countries supporting the wearing of masks relied onAre high ‑ performing health systems resilient against the COVID ‑ 19 epidemic? also on other measures, including extensive testing and self-isolation, and many were better prepared for the epidemic, because they already faced a similar situation in 2003.

In Asia, masks are not just protection, but a confirmation of citizenship and conscience. They are also important as a symbol in other countries. With widespread use, masks can become a signal that society is taking the epidemic seriously, reduce hostility towards sick and reassure people who cannot afford to self-isolate at home and are forced to work in public places.

With all this, there are fears that masks can harm, especially for those who are not used to them. They create discomfort, people touch them, straighten them, move them to wipe their mouths, remove them incorrectly, forget to change.

In addition, due to the shortage of ready-made protective equipment, many sew them themselves. According to researchProfessional and Home ‑ Made Face Masks Reduce Exposure to Respiratory Infections Among the General Population, homemade cloth masks less effective than medical, but still betterTesting the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic?than nothing. Marr advises using thick fabrics for them and sewing so that they fit properly to the face. Reusable masks should be washed thoroughly after use. And it's important to remember that they will not protect you completely.

The mask is a desperate measure for situations where social distancing is not possible. Do not think that if you wear it, then you can freely communicate with everyone.

The debate about the benefits of masks is so intense, because much is unknown, and the stakes are high. “We're trying to build an airplane in flight,” Hanage says. "You have to make decisions with global consequences in the absence of reliable data."

The coronavirus epidemic is evolving so rapidly that years of social change and scientific debate have shrunk to months. Scholarly bickering affects public policy. Well-established rules are changing. An experiment carried out in a hospital room changed people's attitude to the surrounding air in a couple of days. Yes, masks are a symbol, but not only of consciousness. They also symbolize a world that is changing so quickly that there is no time to take a breath.