Staying at least two metres apart from others while indoors has virtually no effect on the risk of exposure to COVID-19, a new study out of Massachusetts Institute of Technology (MIT) says.
The study, released online ahead of its publication in the peer-reviewed journal PNAS on Tuesday, suggests that now-commonplace distancing rules matter far less than the time spent inside with other people, particularly if an infected person enters the room.
The amount of time depends on several factors, according to the study, including the number of people inside, what they’re doing, whether they’re wearing masks and indoor ventilation.
“Above all, our study makes clear the inadequacy of the Six-Foot Rule in mitigating indoor airborne disease transmission, and offers a rational, physically informed alternative for managing life in the time of COVID-19,” the study by MIT mathematics professors Martin Bazant and John Bush reads.
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The so-called “six-foot rule” or “two-metre rule” is still recommended by health officials in Canada and around the world to limit the spread of the virus indoors.
The rule has become common practice since last spring, when the early understanding of the spread of COVID-19 suggested the virus was transmitted by larger, heavier droplets emitted through sneezing or coughing.
However, later studies found the virus also attaches itself to smaller, lighter aerosol droplets that can stay suspended in the air and travel further. Yet the rule has largely stayed in place for businesses and other indoor spaces across Canada.
In an email, Bush told Global News that this latest study effectively created a safety guideline that would limit indoor transmission without a uniform distancing rule.
“It also allows for one to assess the relative risk of various indoor settings, and these assessments turned out to be very interesting,” he said.
In their study, Bazant and Bush developed a formula to estimate how long it would take for a person to be in danger of exposure to the virus if an infected person enters the indoor space.
Using the formula, the pair found the level of exposure could be lower or higher depending on the type of activity, number of people inside and other variables — even if people are more than six feet away from each other.
For instance, the study says a calmer environment with few people allows the lighter droplets carrying the virus to slowly fall to the ground, whereas a high-activity room would keep those particles in the air for longer.
Better ventilation and filtration systems can help limit the spread of the virus even inside a high-activity environment, according to the study.
Bazant and Bush say the formula can also be applied to multi-room spaces like cruise ships, schools and prisons, where ventilation between rooms effectively creates a single “well-mixed space.”
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The study was released along with a website that uses the formula to help users determine how many people could be inside a certain type of room given multiple variables, such as the type of activity and age of the people inside.
For example, the site estimates it would take two days for 25 people wearing masks and talking to be exposed to the virus if an infected person entered the room.
If those 25 people are not wearing masks and speaking, that exposure time drops to 77 minutes. If they’re singing without a mask, they would be exposed in three minutes.
The time falls even more, to 51 minutes, if the infected person is carrying the more infectious B.1.1.7 variant of the virus first discovered in the United Kingdom.
Yet the exposure time also improves if other variables are changed, such as improving the space’s filtration system to HEPA or increasing the total floor area.
Children are also far less susceptible if exposed to an infected person. In that same restaurant with a normal industrial ventilation system, 25 maskless kids who are speaking could stay inside for up to four hours with the original strain of COVID-19 and two hours with B.1.1.7.
The U.S. Centre for Disease Control has adjusted its physical distancing guidance for children in recent weeks, lowering the limit to one metre for K-12 students and summer camp attendees unless they are eating or drinking.
Bush said public health officials in all countries should adapt their rules based on what his and Bezant’s formula revealed.
“We feel that public health orders should reflect the fact that limiting distance between occupants is insufficient to ensure safety in an indoor space, where airborne transmission is also a substantial risk,” he said.
Mask wearing remains the best way to limit both short-range and airborne transmission of the virus, he added, followed by better ventilation and filtration indoors.
