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In that document CDC says that breathing in small droplets and particles (i.e., aerosols) that contain the virus when people are far apart or have been in the same enclosed space for more than a few minutes is UNCOMMON (our emphasis). This will lead people to continue to think that maintaining distance is sufficient to prevent transmission.

We know that transmission at distances beyond 6 feet occurs because of superspreader events, careful studies of smaller outbreaks, and the physics of aerosols. It can easily happen indoors in a poorly ventilated environment, when people are not wearing masks.

There is clear consensus among aerosol scientists and epidemiologists that inhalation of small aerosol particles, including at distances of greater than six feet, is a major driver of the COVID-19 pandemic. To slow transmission and save lives, it is crucial that CDC update its guidance and recommendations to address and highlight the importance of improved ventilation and using NIOSH approved respirators, especially in indoor locations where the virus may accumulate in the air. 

Moreover, OSHA must issue an Emergency Temporary Standard to control workplace exposures, including inhalation exposure, as soon as possible in order to protect workers and reopen the economy safely.

As CDC has made clear, vaccination alone will not stop this pandemic. Mitigation measures are also needed to limit exposures. We must control inhalation exposure of small aerosol particles to end this pandemic. 

CDC must immediately update and strengthen its guidelines and recommendations to protect the public and workers for inhalation exposures to SARS-CoV-2. 

More on the importance of addressing aerosol transmission and the steps needed to control exposures can be found in the letter several of us sent to federal COVID-19 leaders in February 2021.

David Michaels, PhD, MPH

Professor, Department of Environmental and Occupational Health

Milken Institute School of Public Health

The George Washington University

Former Assistant Secretary if Labor for OSHA (2009-2017)

drdavidmchaels@gmail.com 

Donald K. Milton, MD, DrPH

Professor, Institute for Applied Environmental Health

Department of Epidemiology and Biostatistics

University of Maryland School of Public Health

dmilton@umd.edu

301-405-0389

Linsey C. Marr, PhD

Professor, Civil and Environmental Engineering

Center for Emerging, Zoonotic, and Arthropod-Borne Pathogens

Virginia Tech

lmarr@vt.edu and mediarelations-g@vt.edu

Lisa M Brosseau, ScD, CIH

Professor (retired)

Research Consultant, University of Minnesota, Center for Infectious Disease Research and Policy

brosseau@umn.edu

Peg Seminario

Safety and Health Director, AFL-CIO (retired)

pseminario228@gmail.com

Kimberly A. Prather, Ph.D.

Director, NSF Center for Aerosol Impacts on Chemistry of the

Environment

Distinguished Professor

Distinguished Chair in Atmospheric Chemistry

Scripps Institution of Oceanography

University of California, San Diego

kprather@ucsd.edu 

Michael T. Osterholm, PhD, MPH

Regents Professor, McKnight Presidential Endowed Chair in Public Health

Director, Center for Infectious Disease Research and Policy

University of Minnesota

mto@umn.edu

for both reasons of backwardness of the medical-hospital infection control profession and political influences of the AHA and corporate medicine. Their guidance’s list of the five key prevention strategies for K-12 schools, even with the 19 March 2021 update is still not consistent with the scientific evidence. It does not list ventilation, an effective engineering control, as the first key strategy. The general public knows airborne transmission is a reality and the importance of inhalation exposure to infectious aerosols has been extensively covered by CBS, MSNBC, NPR, the Washington Post, the New York Times, the Atlantic and many other mainstream media to the point that a Post journalist told me on March 19th that the topic wasn’t even considered newsworthy anymore. This lack of science-based guidance from CDC, focusing on surface cleaning and not air cleaning, severely complicates the situation for decision makers.

As of March 20, 2021, we are still at high, and most recently, increasing levels of transmission in Maryland and the US generally, even though we are down from the tragic peak levels of early January. This is not a time to relax our vigilance. But we do know enough today, that if we employ the science, we can make schools and workplaces safer and mitigate the serious impacts of school and workplace closures by opening up with stringent controls – and by that I mean not just mask mandates.

The science of worker and building occupant protection from hazardous aerosols and the hierarchy of effective controls is well established. Following the hierarchy of control, it is key to put engineering strategies in place before much less-effective controls that rely on human behavior. The CDC’s recommendations, viewed in light of this hierarch is completely upside down, putting individual behaviors first (masks, distancing, and handwashing) and cleaning and administrative controls (contract tracing) last. Furthermore, the CDC completely fails to specifically recommend the single most effective intervention, ventilation. Instead, they bury mention of ventilation behind sanitizing doorknobs, even though their own scientific briefs acknowledge that touching contaminated objects doesn’t seem to be an important mode of transmission.

To be better protected against inhaling virus floating in the air (and to release less too if you are infected), better fitting masks are important. William Lindsley, a research bioengineer at NIOSH, presented his research at a UMD SPH MIAEH seminar on March 23 showing that there are several ways to make a mask better. Many surgical / medical procedure masks have good filters (not all unfortunately, some good brands are Ambrust and Zubrex, there are others), but they leak a lot around the edges (foggy glasses anyone?). So, get them to fit tighter and leak less you can use a mask brace, a tight fitting cloth mask over the medical mask, or tuck the mask. The brace is best, a cloth mask is good (depends on the mask), and tucking works pretty well too. Tucking seems tricky, but if you watch this video from UNC, it helps get the hang of it.