How improved ventilation can help limit the spread of disease

By John-Paul Glutting

When it became obvious that COVID-19 was a full-blown pandemic, some commentators dangled the prospect of “herd immunity” as the eventual end game.¹ That moment when, either through infection, a vaccination, or both, a sufficient percentage of the population had developed enough immunity to either eradicate the disease outright or dramatically curtail its spread.

And yet, with roughly 95 percent of the U.S. population 16 and older having COVID antibodies from a vaccine and/or prior infection², the COVID waves continue to wash over us, infecting hundreds of thousands every week and killing roughly 300 people a day in the U.S. in June 2022.³

So, how can we live with COVID and equip our workplaces to better manage the current crisis, while possibly prepping for future pandemics involving airborne diseases? Fortunately, we have options.

The pandemic isn’t over

First, it’s important to note that the pandemic will likely to continue for some time, and there’s still no sign that the virus is becoming endemic. What do we mean by that?⁴

Endemic disease levels are the regular, expected levels of disease present in a population, similar to the way malaria is endemic in many countries. On the average, disease levels remain stable over time with an R value (i.e., the number of new cases that will result from every existing case) close to 1. This is in contrast to pandemic diseases, which spread relatively quickly and where each cases spreads the infection to more than one other person. In a pandemic, case counts reach a peak and then decline, although new waves and new peaks can happen in the future. In terms of R value, above 1 when spreading and less than 1 after a peak.⁵

The COVID waves so far, with huge peaks and troughs, are not indicative of an endemic disease, and there is little indication that COVID will settle into an endemic pattern soon, although there may be periods of low activity after large waves, perhaps due to increased immunity in the population. A more likely scenario is irregular, periodic waves as new variants sweep the globe.

The relevant question is not whether to prepare for new waves, but what measures are more effective at reducing disruption.

We can expect COVID waves to end when chains of transmission are effectively cut, either by preventing infections, or building immunity in the global population. So far immunity, particularly vaccine-induced immunity, has reduced transmission and dramatically decreased the rate of poor outcomes from infection, but hasn’t been enough to completely prevent infections with the same or different strains of SARS-Cov2.⁶

Coping with COVID

The level of disruption in workplaces due to illness, exposure to COVID, hospitalizations, disability, and even death, has been enormous. The relevant question is not whether to prepare for new waves, but what measures are more effective at reducing disruption. Any effective strategy must be multi-layered. There are no silver bullets.

Vaccines can offer excellent protection against negative outcomes, including death, when infected with a specific pathogen that vaccine is designed to defend against. However, as we have seen, pathogens can evolve to evade, at least partially, a specific vaccine. There are also logistical challenges to developing, manufacturing, distributing, and administering vaccines to a large population in a short period of time.

It would be ideal if we also had effective measures to put into place both during the development and distribution phase of vaccines, as well as those that could be deployed immediately in response to emergent COVID variants or other airborne pathogens, along with adding an extra layer of protection in addition to vaccines; these measures are widely available and relatively inexpensive when compared with the cost of lost productivity and losses due to sickness, hospitalization, disability, and death.

For example, masks and air filtration can help and can work broadly against a whole class of germs and can be implemented immediately.⁷

Faster is better in a pandemic

A speedy response is important - we have seen repeatedly that new COVID variants spread quickly. A CDC investigation discovered that the first known case of Omicron started showing symptoms on November 22^nd, 2021, four days before the virus was reported to the World Health Organization (WHO).

The importance of air filtration

COVID is an airborne disease, like flu, measles, or whooping cough. Airborne diseases are spread via tiny droplets or aerosols that are distributed throughout indoor air by coughing or even breathing.⁸

Filtering an important portion of these droplets out of the air is possible by using high-quality air filters (MERV 13 or better filters in either in central HVAC units or portable air purifiers) and by using high quality masks (N95, FFP2 or better). Air filtration exchanges ambient air, and masks serve both to contain droplets breathed out by an infected person and to catch droplets before they are breathed in by an uninfected person.⁹

Air filtration has several advantages that make it an intervention that complements vaccination. It can reduce the presence of all currently known COVID variants and many other types of pathogens in the air - it physically removes the germs from the airstream, so molecular changes to spike proteins, for example, become far less of a concern.¹⁰ Air filtration can be put into place relative quickly, as it does not require waiting for new data on a pathogen or profiling the effectiveness of existing immunity.

Augmenting the benefits of vaccines with air filtration interventions can offer advantages.

Key elements of air filtration systems include the size of particles they can filter, the strength of the air circulation system (finer filters require more air pressure and will not work well in systems that cannot generate the required air pressure), and the frequency with which ambient air is cycled through filters. If a new variant begins to spread, most masks will provide some protection from airborne pathogens.

Why vaccines alone may not be enough to stem a pandemic

Vaccines can be effective at reducing transmission and severe outcomes (hospitalization and death):

Only large organizations have the resources to invest in rapid vaccine development of the type we have seen in this pandemic.
While new technologies allow for more rapid development of vaccines than previously, the process still requires many months to complete. Vaccines against SARS-CoV2 took about a year to develop, not including scaling up of production and rollout.
Not all vaccines are 100% effective, so lead time and resources may be completely lost if the vaccine does not work as intended.
Production and distribution of vaccines adds more months to getting an effective level of vaccination in place.
Perhaps most importantly, vaccines are typically developed in response to a novel pathogen and generally cannot be prepared in advance (with some exceptions).

Better air usually equals better outcomes

Augmenting the benefits of vaccines with air filtration interventions can offer the following advantages:

They can be prepared in advance. A MERV 13 filter (along with any necessary HVAC upgrades) capable of eliminating viruses from an airstream can be installed before they are needed to help minimize the spread of pathogens during an outbreak. Masks can also be stockpiled in advance.
Air filtration is not limited to a single pathogen, so it will generally not fail (barring mechanical failure) the way vaccine development can, and many pathogens are not known to become resistant to air filtration the way they can to vaccines or antiviral medications.
Investments in clean air can also reduce allergens, contaminants and seasonal respiratory diseases (flu, colds). Unlike pandemics, these are permanent fixtures of the epidemiological landscape.¹¹
Air filtration is complementary to vaccination. Vaccines only work when a virus enters a potential host, while air filtration can help decrease the number of pathogens encountered, which can reduce the size of “super spreader” transmission events.¹²

Rethinking workplace safety

In-office testing is an important aspect of evaluating the success of an outcome-based policy. Weekly or bi-weekly testing (ideally in the morning) can catch asymptomatic cases before they spread. Good data is important to evaluate outcomes, and the best way to get reliable data is to generate it.

Ideally, implementation of an outcome-based policy is open and transparent – with workers knowing what the safety goals are and how they are being met. Initially, one approach is for a policy that is strict, and when it has been shown to be effective, relaxing protections while outcomes meet pre-established goals. For example, an office could require high-quality air filtration and high air exchange, vaccines for all in-person workers, high-quality masks and bi-weekly testing, with the goal of less than 0.1% of workers testing positive in a 30-day period. If this goal is met or exceeded, it could be relaxed to weekly testing, less masking or both.

A crucial way to ensure the least disruption possible is to reduce transmission, and that requires multiple layers of protective measures.

One advantage of this stepwise type of policy is that it is flexible and can respond to changes in community transmission. SARS-CoV2 is a new pathogen where transmission patterns are not as well-established as other pathogens, for example seasonal influenza. Seasonal influenza generally has established periods when transmission is low, and other periods when it is high. By monitoring reliable data sources, policies can be adjusted when new surges start, new variants spread, or even when seasonal changes indicate that risk is higher or lower.

Boston, for example, has had very low COVID-19 transmission for the last two summers, but not all areas of the U.S. have experienced this lull.¹³ If a seasonal pattern of low summer transmission becomes a reliable pattern in the Boston area, office safety policies may change with the season—masking in the winter, no masking in the summer, for example. Testing requirements may also be relaxed if the rate of community spread is below a reasonable threshold (for example 1/100,000 cases in the general population, or some other threshold determined by respective company policies).

Defense in depth

Limiting the amount of disruption to businesses, schools, and offices has been an implicit or explicit policy goal of governments, corporations, and other organizations since the start of this pandemic. A crucial way to ensure the least disruption possible is to reduce transmission, and that requires multiple layers of protective measures. Not all will be effective in all cases, so it is important to have measures that will prevent spread when others fail.

John-Paul Glutting

John-Paul Glutting is a senior scientist at Verisk. He has a background in public health, bioinformatics, and GIS. Before joining Verisk he worked at the Dana Farber Cancer Institute on computational vaccinology projects (RANKPEP) and the Cochrane Collaboration. His current focus is on human mobility and disease transmission dynamics in global populations. John-Paul has a Master’s degree in public health from the University of Massachusetts, Amherst, and an MS in geographical information science from the Vrije Universiteit, Amsterdam (Netherlands).

Vent to prevent: How improved ventilation can help limit the spread of disease in workplaces