Year Two of the Covid-19 Pandemic: Vaccines, Masks, and Airborne Virus Particles

By Dr. Winnie Chu

After almost two years, what do we know for certain about the rapidly mutating and spreading Covid-19 virus? What have we learned about best practices to protect the workforce and the public? As the virus becomes more infectious, can we do more?

Acceptable workplace Covid Protocol

Thanks to the development and adoption of Covid-19 safety protocols, people can finally travel and reunite with loved ones after nearly two years of international border closures. Most countries now require travellers to be fully vaccinated and undergo a molecular, antibody or antigen test before arrival. Acceptable masks must be worn during flights. In the workplace, currently implemented safety measures include maintaining social distancing, disinfecting surfaces, wearing masks, vaccinations and/or molecular or antigen tests for employees, as well as enhanced ventilation and frequency of air changes to remove airborne viruses.

Masks, Vaccines and Covid-19 tests

Thanks to the critical collaboration and research efforts of the world’s leading pharmaceutical companies, many of us are very fortunate to have received first and second doses of a Covid-19 vaccine (and even a booster shot!). Just when daily life was looking almost ‘normal’, we now face the newest and even more transmissible Omicron variant. At this point, the vaccine efficacy of three doses against Omicron is still unknown (January 1st, 2022). Hopelessly we watch as restrictions are reinstated and infections rise exponentially once again around the globe. Many Occupational Health professionals wonder what we can do, and must do to better protect humanity from airborne diseases now and in the future.

Industries and governmental agencies worldwide have adopted policies of implementing rapid antigen testing several times a week for all employees. However, rapid antigen testing is only as practical as it is economical, and false negatives are not uncommon, even when administered properly. Molecular (PCR) tests are much more accurate than rapid antigen tests, however false negatives are still reported especially when testing is performed several days after symptoms begin.

All of us, winter or summer, children and adults, have gotten used to wearing masks. N95, PN95, surgical types and even cloth masks are recognized as a useful layer of defence against SARS-CoV-2, even though it is ingrained in hygienists’ minds that for any given mask to be effective, a proper fit test must be carried out. In fact, an individual Covid-19 virus has been measured under negative stain electron microscopy to be about 100 nm wide with club-shaped surface projections surrounding the periphery of the particle (C.D. Humphrey). Even if all masks were fit-tested and passed, the estimated filtration efficiency is only around 75% against particles of 100 nm diameter when using a fibrous filter. This may explain why despite the use of personal protective equipment’s to filter virus containing aerosols, there are multiple reports of workplace transmission of Covid-19 potentially through the inhalation of viral particles in small aerosols [1]. Obviously, it is crucial to add yet another layer of protection against the spread of highly infectious airborne viruses.

World First Live Real-World study on the monitoring and removing of Covid-19 aerosols, now
a preprint for peer-reviewed publication

Far-UVC (207 to 222 nm) light disinfection is shown to reduce live coronavirus by 99.7 percent in 30 seconds. Whenever air is the major mode of transportation, portable ventilation systems with far-UVC and high-frequency air changes to improve ventilation are considered to be a more effective control against infection comparing to other techniques [2]. In October 2021, with the support of Cambridge University Hospital NHS Funding, Addenbrooke’s Hospital (Cambridge UK) has concluded the first real-world studies by sampling and providing evidence of airborne Covid-19 viruses in hospital wards. They also demonstrated the removal of airborne SARS-CoV-2 viruses from the air using portable air filtration systems with far-UVC and high air changes (BBC interview)[3].

BBC interview

Sampling Covid-19 Aerosols

Sampling of airborne viruses was conducted using a two-stage cyclone with microcentrifuge tubes created by the National Institute for Occupational Safety and Health (NIOSH) to collect airborne particles with cut-off diameters of 2.6 micrometers and 1.6 micrometers at 2 L/min with subsequent PCR assays [4]. A NIOSH BC251 two-stage cyclone aerosol sampler was created to allow bioaerosol samples to be readily analyzed by polymerase chain reactions (PCR) or enzyme-linked immunosorbent assays (ELISA). The Cambridge/Addenbrooke’s study was conducted over both an intensive care unit (ICU) and a repurposed ward for managing patients infected with SARS-CoV-2 (presumably without high-frequency air changes).

Figure: NIOSH BC251 two-stage cyclone bioaerosol sampler
In both the ICU and the repurposed COVID ward, airborne SARS-CoV-2 RNA was detected in air samples on all five days using the NIOSH BC251 two-stage cyclone and subsequent PCR assays. However, none was detected during a five-day repeated sampling when a far-UVC filtration system with high-frequency air changes (Maxvac Medi 10) was turned on in the wards. After the portable filtration system was turned off, SARS-CoV-2 was again detected during 4 out of 5 days of sampling.

Adding another layer of protection to workplace and the public

It is important to note that the data also showed that viral particles were present in areas that were NOT considered to be aerosol risk areas. Given the ongoing and future threat of airborne infections, in addition to all current safety protocols and layers of protection, it is strongly recommended to enhance indoor ventilation systems (for example, with the use of plugin-ready portable far-UVC systems with high-frequency of air changes). Airborne Covid-19 particles have been found to be viable for as long as three hours. Small particulates such as 100 nm viruses can be sustained in the air for long periods of time. Therefore, short- and long-term ventilation solutions may provide additional safety to prevent the spread of viruses in workplaces and public areas. It is also crucial to establish a routine aerosol sampling and management program for ongoing indoor air surveillance to determine the effectiveness of current monitoring programs against Covid-19 and other potential infectious bioaerosols.

Please feel free to contact us if you would like to learn more about various air purifier options or to find out how to collect aerosol samples to enable us to assist with managing aerosol removal methods for your specific situation.

Best regards,
Dr. Winnie Chu