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The Infection Prevention Strategy (TIPS)

Jun 21, 2021

In July 2020, scientists citing the precautionary principle said “It Is Time to Address Airborne Transmission of Coronavirus Disease 2019 (COVID-19)”. They were rebuffed a month later by experts who cited a lack of evidence and argued: “the concerns raised by the authors are not borne out in clinical experience”. Nearly a year later, the Centers for Disease Control (CDC) and the World Health Organization (WHO) updated their language to include aerosol transmission and in the case of the CDC, they listed it as the first method of transmission before droplets and fomites. Paradoxically, neither organization updated its guidance to address the implications of the new language. What’s going on here?

Today’s guest is part of a growing body of experts calling on the Infection Prevention and Control (IPAC) community to accept that SARS-CoV-2 is not only transmitted by aerosols but that the airborne route may be the dominant mode of transmission. Dr. David Fisman, an epidemiologist and professor at the Dalla Lana School of Public Health, along with several colleagues, published Ten scientific reasons in support of airborne transmission of SARS-CoV-2. Dr. Fisman tells us that the evidence is clear, but the IPAC community has been slow to accept it because of two main reasons. First, IPAC practitioners are going to lose face – to change course now is to admit they were wrong. Second, this will cause a massive change to IPAC practices in hospitals – some at significant expense.

Dr. Fisman believes the Semmelweis reflex – the human behavioral tendency to stick to preexisting beliefs and to reject fresh ideas that contradict them despite adequate evidence – may be at play. Zeynep Tufekci said something similar in a recent NY Times article when she said IPAC experts were “setting a higher standard of proof for theories that challenge conventional wisdom than for those that support it.” And TIPS previously described this type of thinking as Highly Qualified Toxic Culture Syndrome.

This resistance to new thinking could be supported by the massive implications (and costs) that would be driven by necessary changes to IPAC protocols. Plus, we cannot discount the effects of the highly charged political environment on every aspect of the pandemic response. Regardless, Dr. Fisman makes a compelling case that it’s time for the IPAC community to take a step back and reevaluate the growing body of evidence that points to aerosols as the dominant means of SARS-CoV-2 transmission.

In addition to the droplet vs aerosol debate, we cover:


  • The history of the Dalla Lana School of Public Health and the newly founded University of Toronto Institute for Pandemics
  • David Fisman’s background and career path
  • What it’s like being an epidemiologist during a pandemic and working under the microscope in a highly charged political environment.
  • Dealing with misinformation.
  • COVID-19 origins
  • Treating vaccine manufacturing capabilities as a strategic asset for national security.
  • The Ontario government’s reopening plan and how it seems to acknowledge aerosol transmission without explicitly saying it.
  • Vaccine mixing
  • And much more


You can also catch Dr. David Fisman and others discussing aerosol transmission on CBC’s recent story: How delays in acknowledging airborne COVID-19 transmission risked lives.