Defeating corona: Listen to the science

What is the science anyway? And what should we be doing, according to medical experts?

Dr. Noam Gavriely (photo credit: Courtesy)
Dr. Noam Gavriely
(photo credit: Courtesy)
Political leaders in Israel and abroad repeatedly chant the same mantra: We must all listen to the science – meaning, listen to the medical experts and do what they say, to combat the COVID-19 pandemic. But more than once, politics has drowned out science.

What is the science anyway? And what should we be doing, according to medical experts?

Here are clear answers from two Israeli doctors with some 80 years of experience between them: Dr. Noam Gavriely, formerly vice-dean of Technion-Israel Institute of Technology’s medical school and Dr. Pinchas Halpern, until recently head of emergency medicine at Tel Aviv’s Ichilov Hospital, part of the Sourasky Medical Center.

Dr. Gavriely is a world expert on pulmonary illness, founder of Karmel Medical and inventor of the ViriMASK (Jerusalem Report, April 6). Dr. Halpern has vast experience and has done extensive research on intensive care medicine. What follows summarizes two detailed scientific reports written by Dr. Gavriely, and by Dr. Gavriely together with Dr. Halpern.

As of September 1, 117,000 people in Israel had COVID-19; of these, 939 died and 95,000 have recovered. More than 20,000 are ill and recovering. Some 1.2% of the population, that we know of, has been infected. Of those infected, 0.8% have died. Worldwide, there have been 25,334,339 cases and 848,000 deaths. Some 22% of global deaths occurred in the US, where there have been six million cases and a death rate of 3%.

How serious is COVID-19 and how does it spread?

“To gain a perspective, let’s examine the corresponding data regarding the seasonal flu. In the last decade, between 2.8% and 13.6% of US residents have been infected with flu every year. Among them, 0.13%-0.14% died. So the number of flu patients is much larger than the number of COVID-19 sufferers, but the mortality rate among those who contracted corona is 10 or 20 times higher. This makes the novel coronavirus a much more dangerous disease than the seasonal flu.

“Epidemics are like a nuclear chain reaction. As the patient emits more viruses and as more people are near the patient, the more active a chain reaction of infection is generated. The presence of many patients emitting viruses close to vulnerable people increases the risk of spreading the infection. Maintaining distance slows down the chain propagation.

“As of today, we do not know the ‘minimal infective dose’ [the smallest amount of virus needed to cause infection and illness]. We must assume that in a certain unknown number of cases it is sufficient to have a single virus penetrate and root to cause the disease.” Which type of mask is most effective? Why is hard to breathe with masks?

“N95 masks are called this because they block 94-95% of particles between 0.1 and 3 microns [a micron is a millionth of a meter]. N99 masks block 99%.

“It is hard to breathe with N95 and N99 masks. There are three reasons.1) Resistance to air flow through the mask. 2) Accumulating carbon dioxide and decreased oxygen, and 3) Heat load and humidity. The air we exhale contains 100% humidity at a temperature of 37°C.

“Protective gear used by everyone can reduce interpersonal transmission by between 50 times to 10,000 times, depending on the masks.”

Why are commercial airline flights risky?

“The passenger cabin on commercial flights contains pressurized and warmed up air. Airlines try to save money by reducing the replacement of air in the cabin. Instead they use filters that can block particles. It is enough that one person coughs and sheds viruses in the passenger compartment for the viruses to reach all passengers and cause infection. To cope with this, we should use filters that can filter out virus particles, 0.1 microns and above and demand that passengers and flight personnel use the best available personal protection equipment (a full-face mask with eye protection).” What exactly is “aerosol dispersion?”

“With each cough and sneeze, there are very small particles under 10 microns in diameter, especially those under 2.5 microns, that tend to remain suspended in the air for a long time. This aerosol is scattered all over. While the volume of these particles is low, their surface area is large and lots of virus particles can stick to the surface of these small particles. It is now fully accepted that the virus’ transmission by aerosols is an important vector. The relatively large area of the eyes’ surface makes them vulnerable to the landing and culture of viruses. Protection against sprays and eye protection are crucial to creating barriers against contracting COVID-19.

“Cough is the dominant mode of spread and as such should be monitored in areas where people congregate to assess risk in an objective mode and to identify possible spreaders. Cough monitoring is feasible with devices being available and used in pulmonary and occupational contexts.” What is the difference between ‘infected’ and ‘infectious?’

“A person must be infected with the virus in order to be a vector of spreading COVID-19. However, not all infected patients are spreaders. Early on after a person becomes infected, the virus is confined to the body’s cells and has not yet replicated sufficiently to be identified by a PCR test [polymerase chain reaction, a standard method for multiplying virus so it can be better detected]. The patient may already test positive, by PCR, but does not yet shed viruses. In fact, there are data to show that the most positive PCR values are seen hours before the symptoms begin. On the other hand, spreading becomes most intense when patients start coughing and develop fever. This is because coughing is the most intense mode of disseminating the virus. Cough and the amount of air a person inhales and exhales per minute may be the strongest predictors of infectiveness – the ability to infect others.

How do we know when it is safe to open schools, shops, restaurants, etc.?

“Five key points:

1. What is the expected viral load? Clearly, the load in a coronavirus hospital ward is much larger than in places where the chance to encounter a virus spreader is low. The number of carriers in a community divided by the population can be used as a simplistic benchmark. For example, in the city where there are 100,000 inhabitants and 100 active patients, the expected statistical load is 0.1%.

2. Is the air in the place in which we are staying replaced with fresh air frequently or filtered? Obviously, in a space that refreshes the air in a controlled and measured way, the risk decreases. For example, if the air in a hall that has a volume of 300 cubic meters is refreshed 10 times an hour by using a pump that can blow 3,000 cubic meters per hour, the concentration of virus particles is reduced 10 times, thereby reducing the risk or allowing more people to share the space. Another option is to move the air through dense filters that are able to block the virus particles.

Frequent replacement of the air in an enclosed space (e.g. one hundred times an hour) is an effective measure for reducing risk of spread, particularly where masks cannot be donned (as, for instance, in dining).”

3. Shielding: Protection should always be two-way, i.e. the protective mask protects both the user and the environment. For example, the paper mask, or “surgical” mask that most of us use, prevents the distribution of droplets emitted while coughing and sneezing at a level of about 85% when used correctly (on the nose and mouth together).So, when two people wear an 85% paper mask, the total risk of transferring a virus is 15% times 15% or 2.25%. This is a very significant drop in overall mutual risk. For N95 masks, the risk of mutual exposure drops to 0.25%, or nearly one-tenth, and for N99 masks, the mutual risk is only 1% times 1% or a negligible 0.01%.

4. Distance. The concentration of particles in the air decreases with the distance. Over time, the particles disperse and occupy the entire space. Assuming the size of the space is about 50 cubic meters, or 50,000 liters of air (a 4x4x3.1 m. room), release of, say, a million particles floating in one liter is diluted 50,000 times. So, if a “virus shedder” stands in the middle of the room, a person 2 meters away, near the wall, is exposed to a very small concentration of virus. Social distancing is therefore an important tool in reducing the viral load and the risk of infection.

5. Susceptibility and vulnerability: What is the concentration of particles that is dangerous for us? Science on this subject is still unclear. For SARS (bird flu), a member of the corona virus family, it was found that several hundred virus particles are necessary to cause the disease. However, for patients with immunodeficiency disease, such as patients receiving steroids, dialysis patients, and those receiving cytotoxic drugs (used to kill cancer cells), we should assume that in some cases even a single virus can penetrate into a cell and begin to reproduce.

“Keeping a distance of two meters is effective to avoid spread by droplets emitted during cough. But it is not sufficient to prevent transmission of suspended airborne small particles (aerosols) and therefore combining social distancing AND masks is highly recommended.” Case Study: Two Women

“Two recent cases depicted on an Israeli TV program illustrate the importance of the presence of symptoms to predict infectiveness. Two women who recovered from COVID-19 were interviewed. Both tested positive a day or so after entertaining their respective extended families on a recent holiday.

“One of them had symptoms (cough, fever) that started on the morning of the party; the other had the symptoms start 24-48 hours after the party. The first had infected many of the participants. The second had no family members infected. Clearly, this cohort is non-scientific and too small. But it serves as an illustration of the fact that cough and hyperventilation due to fever enhance infectiveness.” What about the risk involved in exercise?

”If you compare a person resting and breathing about 6-7 liters per minute, and a person doing physical effort and breathing 60 liters each minute, it is clear that the total burden of the virus exposure grows in proportion to the amount of air that penetrates the lungs.” What about eating in restaurants?

“There is risk in eating in restaurants where masks cannot be used. It is mandatory to intensively ventilate a dining area by outward-pointing efficient fans, not just to mix the air (which actually increases the risk).”

What is the ‘viral load’ outdoors?

The dilution in open air is immense. Consider the following example: A soft wind is blowing at 3.6 km/hour (2.2 miles per hour). If we consider a four-meter-long test volume of air, the flow of air in the wind will sweep the test volume in four seconds, or nearly a thousand times per hour. This is significant and should be sufficient to prevent infection if very sporadic individuals are present. But if a distance of two meters cannot be observed at all times, the risk level is such that the use of a mask, at least surgical or cloth, is still required in the open.

“Rain is a good scrubber, so outdoor activities may not need to be restricted, whether for social and cultural gatherings, exercise or political rallies, as long as masks are worn and distance is maintained.

What are your main recommendations, based on the science?

“When rationally examining the protection against coronavirus, the cost must also be taken into account. You can’t completely ignore it. It is not cynical to calculate the financial value of saving a person’s life in a situation where the size of the ‘cake’ is finite and should be prioritized as rationally as possible. In a situation where billions of shekels are invested in coping with the economic damage of closures and the loss of jobs, a national investment should be considered in the distribution of protective masks at level N99 for the entire population, or at least the population at higher risk.” Is there a technology that could bring a real breakthrough?

“Yes. Ambient monitoring, or ‘sniffing,’ of VOC’s, volatile organic compounds, specific to COVID-19, may be possible in future. [This technology could detect very small amounts of COVID-19 virus in people’s breath, instantly]. This may become the ultimate risk assessment and mitigation tool going forward.” What is your take-home message?

“So, the take-home message is that everyone must understand the basic science of virus spread and protection. It is fairly simple and empowers us all in our permanent quest for the balance between personal safety, societal responsibility, and maintaining normalcy in our lives. Meet outdoors as much as possible, wear efficient masks, keep your distance, avoid crowds, wash your hands. It’s rather simple, isn’t it?”
The writer heads the Zvi Griliches Research Data Center at S. Neaman Institute, Technion and blogs at