News

This summer, as COVID-19 continued its spread across the U.S., the National Academies brought together engineers, virologists, public health experts, and others for a meeting to dive into the rapidly evolving science of COVID-19 airborne transmission. Can the virus be transmitted by speaking or breathing? How long do particles in the air stay infectious? And how far can they travel? What questions have we yet to ask?

To date over 15,000 people have watched the virtual two-day workshop, and last week, the National Academies published a summary of the session, providing a valuable snapshot for the scientific community of what is being learned about COVID-19 and airborne transmission.

As a member of the Academies’ Environmental Health Matters Initiative steering committee, Jonathan Samet, a pulmonary physician and epidemiologist who serves as dean of the Colorado School of Public Health, helped plan the workshop. Samet answered questions about the impact of the event, and how the research community can use the new summary in their ongoing, urgent research into COVID-19.

Q: What was the goal of hosting a workshop that brought together researchers from divergent fields — such as engineering and public health?

A: The topic of the workshop — airborne transmission of SARS-CoV-2 — is inherently multidisciplinary. In this workshop we wanted to give scientists from different areas a space and framework to break down their silos and hear what their colleagues in other fields were working on. Controlling the COVID-19 pandemic, as we all know well by now, is not a problem just for one discipline. It requires clinicians, public health researchers, behavioral scientists, virologists, and aerosol engineers all working together and approaching the problem from different frames to find solutions that are helpful for communities and decision-makers responding to the pandemic.

One of our other goals was to bridge the terminology gap — researchers and others were using different terms to describe infectious particles without standardization (droplets versus aerosols). The workshop gave us all a chance to make sure we were on the same page and avoid confusion. 

Q: What did we learn about airborne transmission of COVID-19 from the workshop that previously hadn’t been shared or understood?

A: The science has advanced rapidly on airborne transmission of SARS-CoV-2, not surprisingly given the many gaps in understanding and the urgency of filling them. Above all, I was impressed by the strength of the evidence for airborne transmission by both larger particles (droplets) and smaller particles (aerosols). Transmission by aerosols is particularly important because they can travel across rooms. The workshop took on the challenge of carefully defining droplets and aerosols and made a proposal about the size cut-off dividing them.  This should help to bring some uniformity to discussions of airborne transmission. 

During the workshop we also learned more about the size range of aerosols generated by people infected with SARS-CoV-2.  These aerosols were shown to be an important transmission pathway by the presenters. The workshop also touched on concentrations of the virus in the air under different circumstances, and how the highest concentrations of aerosols are closest to an infected person. These discussions have important implications for mitigation measures like masks and physical distancing. 

Q: Which presentations and discussions did you find most surprising?

A: I found the indoor air presentations and discussions encouraging and surprising. Although we know that the risk of transmission is higher indoors than outdoors, strategies to address this increased risk had not been discussed widely, so I appreciated these being articulated at the workshop.  The workshop addressed the importance of having adequate ventilation (providing fresh air) for indoor spaces and the potential benefit of air cleaning.  Before the workshop, I had not appreciated the extent of the evidence on the benefits of wearing masks, both to protect others, particularly from sprayed droplets, and to protect the wearer.

Q: What has been the impact of the workshop?

A: This workshop addressed a critical topic for this point in the pandemic. We were pleased that thousands of people tuned in to the workshop live, giving it impact right from the beginning. We were fortunate to have scientists participate who are passionate about sharing the results of their research and communicating them in an effective way. All speakers were well prepared and gave excellent presentations that together painted the full picture on airborne transmission.  They were attentive to translating their research findings so that they were useful for those outside of their discipline, and helping others understand how new information on the virus can be applied in the real world to pandemic control. To date we’ve had about 15,000 views of the workshop, and people are still watching it and sharing it.

The issue of whether COVID-19 is airborne, what that means, and what can be done about is has been one that the media has focused on over recent months, and we know that reporters were able to learn from the session and reference it in their work. I think our workshop and the proceedings we just released provide a snapshot of where knowledge stands on airborne viral spread, and synthesize what we’ve learned as a scientific community.

Perhaps most importantly, I think the workshop gave the public a view of scientific understanding of how COVID-19 spreads through the air. We were clear with viewers during the workshop about what we do and don’t know yet.  And I think that such transparency is critical as we move forward to reduce airborne transmission through evidence-based policies. 

Q: How do you hope the workshop proceedings and recorded presentations will be used?

A: I’m hopeful that the workshop’s discussions will impact control approaches. The clarity developed around aerosols versus droplets, as laid out in the proceedings, will serve as a reference for further work in this space. The workshop also highlighted research needs. And, I hope the proceedings will be a helpful reference for the public and decision-makers going forward.