Why N95 Masks Fail to Stop the Spread

 Since the beginning of the pandemic, we have been assured that community masking compliance would solve our problems and halt the spread of SARS-CoV-2.

• Yet real-world application data has consistently shown them to fail as a mitigation measure for personal protection, and instead of correcting course on the haphazard guidance that was doled out, we were told to mask harder with increasingly restrictive, albeit effectively non-mitigating apparatuses.
• Here, we look at the output, particle- to- PFU ratio, and MID for N95s versus the hypothetical perfect capture capacity for NGCs.

Particle ranges and corresponding behavior of emitted matter

• Pandemic mitigation measures should have begun with minimum viable particle size, which for SARS-CoV-2 falls at 0.06-0.14 µm.
• More than 90% of exhaled particulates have been shown to fall under 0.3 µm, and matter remains aloft for extended periods - hours, even days, depending on air exchange rates within the given space.

Respiratory Emissions from "Sick" Patients

• PCR-Positive versus Negative Test Results
• 90%+ percent of emitted particulates by PCR-positive test subjects were under 0.3 µm, and counts of emitted matter were conducted comparing individuals with different severities of illness with PCR-negative subjects.
• If we use a respiratory emission rate of 4.3-29 liters per minute (from the EPA Exposure Factors Handbook), the highest-output range of 34,772 particles per liter multiplied by 29 liter per minute is as high as 1,008,388 particles emitted per minute.

Particle Sizes and Emission Rates

• The study previously discussed measures- emitted particle- size ranges in SARS-CoV-2 positive and negative subjects.
• Particle size distribution
• Available size channels (in total, 14 size channels from 0.15 to 5.0 μm) were analyzed in across three size bands: <0.3 μm, 0.5-5.5 μm and >0.9-10 μm
• For both groups, the majority of the aerosols (>90% in the SARS–COVID-positive group and >78%
• in the -negative group) were found in the smallest range (<0. 3 μm).
• Increases in total aerosol concentration were dominated by increases in particles ≤ 0.3μm.

The presence of RNA copies versus concentrations of viable virions

• Not all RNA copies or virus particles are capable of forming PFUs resulting in viral replication
• These are estimates on total viral production during an infection.
• "Dividing by estimates for the inverse of the viral clearance rate gives an estimated total production of 3 × 109 to 3 × 1012 virions,"

Virion output

• Different methods of establishing virion output offer slightly different ranges when viewed side-by-side
• Some studies show total virions emitted
• Others give total particle counts
• What is important to establish is that overall virus particulate output does not equal total viable virions, meaning virions capable of creating Plaque Forming Units (PFU).

PFUs

• Understanding virus particles needed to form individual Plaque Forming Units (PFU)
• One viable viral particle, or virion, is capable of creating one PFU, in which this viral particle replicates.
• The relationship between the total output of particles and the creation of PFUs is called a particle to PFU ratio.

PFU and Minimum Infective Dose Studies

• The average human respiratory rate is 16-20 breaths per minute.
• We will look into output as virions per minute, and minimum infective dose as PFUs and virions for transmission, as both are explored in available research.

Minimum Infective Dose (MID)

• Comparison studies of different respiratory viruses and SARS-CoV-2 animal studies have been used to contribute to many MID estimates, but this paper focuses solely on human studies as much as possible.
• The minimum infective dose of COVID-19 in assessed cross-sectional and case-series studies was low, and infection rates were comparable to other coronaviruses.
• Children had lower live virus growth, higher cycle thresholds, and lower viral concentration in comparison with adults, so children are not the main carriers of infection.
• The infection rate in children was lower than other groups (125 PFU).
• N95s provide meaningful protective value from infectious aerosols by looking at output contributions, infectivity potential of emitted viral matter, PFU ranges, then we can weigh these ranges against a hypothetical perfect capture capacity of N95S capturing 95% of matter, versus the remaining uncaptured 5% percent.

Why N95s failed/are failing/will fail

• Respirators with an N95 rating are designed and approved to capture 95% percent of non-oil-based matter greater than 0.3µm.
• For the purpose of an exercise in hypothetical perfect capture capacity, we will grant them an assumption of perfect 95% rate of capture
• If we apply 5% of the MID figures demonstrated in to demonstrated in output ranges A and B, it will demonstrate the infectivity of viable virions versus the 5% percent never captured

Summary

• We became lax with our mitigation standards during the SARS-CoV-2 outbreak because this pathogen is not fatal for the overwhelming majority of people, with a survivability rate shown around 99.8% percent
• This flippancy toward a hazard-specific response is incredibly dangerous when applied to deadlier pathogens and exposure elements

Glossary

• aerosol - particles dispersed in air or gas, defined as less than 5 microns in size
• asymptomatic (spread) - the theoretical concept of transmitting a pathogen to others while not exhibiting any established symptoms of said pathogen
• Atmospheric saturation - the amount of viable matter that remains aloft within an enclosed space
• emissions - exhaled respiratory matter
• minimum infective dose - the minimum amount of a hazard one must be exposed to in order for onset of illness to be anticipated
• PCR-negative - a given test subject does not receive a positive test result when tested with PCR methodology for a given pathogen; PCR-positive = positive test using the polymerase chain reaction technique
• perfect capture capacity - capture of hazardous matter at a matched percent efficacy given by a product as its hypothetical best rate possible

https://brownstone.org/articles/why-n95-masks-fail-to-stop-spread/