Slipstream: Can You Get COVID-19 by Walking Behind Someone?


Getty An elderly lady uses nordic walking sticks on September 23, 2010, in Berlin, Germany.

Americans are living under new social distancing requirements that did not exist in everyday life before the COVID-19 coronavirus pandemic. And according to new research that has been conducted by universities in the Netherlands and Belgium, Americans may need to do even more.

*Before continuing, it is key to note that this study has not been peer reviewed and it has received criticism — that will be covered later in the article.

The research suggests that even though keeping 1.5 meters (5 feet) between individuals standing still indoors or outdoors in calm weather is “very effective” in reducing the risk of transmitting COVID-19, runners, walkers, and cyclists need to avoid another individual’s “slipstream.”

The study states, “If someone exhales, coughs or sneezes while walking, running or cycling, most of the microdroplets are entrained in the wake or slipstream behind the runner or cyclist.”

The study was done through a joint effort by the Eindhoven University of Technology in the Netherlands and KU Leuven in Belgium.

Bert Blocken, a professor of civil engineering at Eindhoven University of Technology and KU Leuven and the lead researcher for this study explained to the Independent:

The slipstream is the zone that arises right behind a person when they are walking or cycling, and which pulls the air a bit along with this moving person, as it were. Cyclists like to position themselves in the slipstream of others to reduce their air resistance. But someone who walks or runs also has such a slipstream. We have seen that no matter how that zone forms, droplets end up in that air stream. So it’s best to avoid that slipstream.

Here is a video shared by Blocken that illustrates what the slipstream would look like in different arrangements:

The video shows that walking behind someone at 4 km/h (2.5 mph) is less safe than walking beside that person or talking to someone 1.5 meters away.

The video concludes that walking in a “staggered” formation at 4 km/h is safer than walking behind someone. Blocken has made it clear that he does not want to discourage anyone from exercising; he simply wants people to avoid others’ slipstreams when they do so.

To reiterate: this study has not been peer-reviewed, meaning the research needs to be evaluated and validated by other scientists and organizations before it can be considered scientifically factual.

It has not been proven if an individual is at higher risk of contracting COVID-19 by being in another person’s slipstream.

The Study Has Received Criticism for Not Being Peer-Reviewed

The study has received some backlash because the research was released by Blocken and his team before being peer-reviewed. Blocken’s findings and processes have not been meticulously studied by other scientists and organizations, which is typically done before scientific research is shared publicly.

William Hanage, an epidemiologist at Harvard’s Center for Communicable Disease Dynamics, spoke with Vice. He said, “On the epidemiology side—where the droplets are is much less relevant than the amount of transmission that occurs via this route. Advice on physical distancing is really about *reducing* the risk of transmission rather than eliminating it altogether.”

Hanage believes the Blocken’s study is not “really useful — not to epidemiologists anyway. The amount of transmission from this route even if it is possible will be dwarfed by that from others.” He also said the research was pushed out and went viral too quickly.

Blocken told the Independent:

It’s interesting to see studies can easily be misinterpreted. Most people understood the message in a positive way, but there were two misconceptions. One misconception is that we make statements on virology. We only tested distance to the exposure of droplets. That’s aerodynamics; how do droplets behave in the airflow? I didn’t make any claims that infection rates would be higher or lower.

And some people have said that I advised against going outside, running or cycling, which is the opposite of my intention. I am a keen cyclist myself. They should go out, but they should be careful. If you move too close to another person, stay out of their slipstream, but if you want to be in slipstream, keep a longer distance.

The Researchers Turned the Research ‘Upside Down’ Because of the Urgency of the Situation

The researchers addressed why they have not had the research peer-reviewed. They said they felt the situation was too urgent and the pandemic too wide-spread, so they made an exception and “turned things upside down.”

They said they started by making the research results available to the public and only submitted the proposal for further research funding after the fact. They plan to submit the article for peer-review later. The researchers added: “We thought carefully about this reversed order. Given the situation, we decided it would be unethical to keep the results confidential and keep the public waiting months for the peer review process to be completed.”

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