Customers dine at Picos Restaurant, which was threatened after the announcement of its continued need for masks as the state of Texas prepares to lift its mask mandate and shut down business during the coronavirus disease (COVID-19) pandemic in Houston, Texas to fully expand again. March 9, 2021.
Callaghan O’Hare | Reuters
The risk of being exposed to Covid-19 indoors is just as high at 60 feet as it is at 6 feet – even when wearing a mask. So, according to a new study by researchers at the Massachusetts Institute of Technology, who are questioning the social distancing guidelines adopted around the world.
MIT Professors Martin Z. Bazant, who teaches chemical engineering and applied mathematics, and John WM Bush, who teaches applied mathematics, developed a method of calculating the risk of exposure to Covid-19 indoors that takes into account a variety of issues that have an impact could be transmission, including time spent inside, air filtration and circulation, immunization, variant strains, mask use, and even respiratory activity such as breathing, eating, speaking, or singing.
Bazant and Bush question the Centers for Disease Control and Prevention’s long-standing Covid-19 guidelines and the World Health Organization in a peer-reviewed study published in Proceedings of the National Academy of Science of the United States earlier this week has been.
“We don’t think the 6-foot rule is of much use, especially when people are wearing masks,” Bazant said in an interview. “It really has no physical foundation as the air a person breathes while wearing a mask tends to rise and fall elsewhere in the room, leaving you more exposed to the average background than a person in the distance.”
The important variable that the CDC and WHO have overlooked is the amount of time they spend indoors, Bazant said. The longer someone is in the house with an infected person, the greater the chance of transmission, he said.
Opening windows or installing new fans to keep the air moving could be just as effective or more effective than spending large sums of money on a new filtration system, he said.
Bazant also says the guidelines for enforcing indoor occupancy limits are flawed. He said that 20 people gathered for 1 minute is probably fine, but not over several hours, he said.
“Our analysis also shows that many rooms that have actually been closed do not have to be closed. Often the room is big enough, the ventilation is good enough, the time people spend together is so big rooms can be even at full capacity safely operated, and the scientific support for reduced capacity in these rooms really isn’t very good, “Bazant said. “I think if you enter the numbers, even now, for many types of rooms, you will find that no occupancy restrictions are required.”
Six feet of social distancing rules accidentally leading to closed businesses and schools are “just not sensible,” according to Bazant.
“That emphasis on distancing was really misplaced from the start. The CDC or the WHO never really provided a justification for it. They just said that this is what you have to do, and the only justification I know of is based on coughing and sneezing studies that look at the largest particles that could settle on the floor, and even if it’s very approximate, you can certainly have large droplets of greater or shorter range, “said Bazant.
“The distancing doesn’t help you that much and also gives you a false sense of security because you’re just as safe at 6 feet as you are at 60 feet when you’re inside. Everyone in this room is about the same risk actually,” he noted.
Droplets laced with pathogens move through the air indoors when people are talking, breathing, or eating. Airborne transmission is now known to play a huge role in the spread of Covid-19 compared to the earlier months of the pandemic when hand washing was seen as the top recommendation to avoid transmission.
These droplets from the warm exhalation mix with body heat and air currents in the area and rise and travel across the room, no matter how socially distant a person is. According to the study, people seem to be more exposed to this “background air” than distant droplets.
For example, if someone infected with Covid-19 wears a mask and sings loudly in an enclosed room, a person sitting on the other side of the room is no better protected than someone just three feet from the infected person sitting person. Because of this, the time you spend in the confined area is more important than the distance from the infected person.
Masks generally prevent transmission by blocking larger droplets. Therefore, larger droplets don’t make up the majority of Covid infections as most people wear masks. The majority of people who transmit Covid do not cough or sneeze, they are asymptomatic.
Masks also prevent transmission indoors by blocking direct clouds of air. The best way to see this is when someone is exhaling smoke. Continuous exposure to direct infectious air plumes would result in a higher risk of transmission, although exposure to direct air plumes usually does not last long.
Even with masks on, such as when smoking, those in the vicinity are severely affected by the second-hand smoke that moves and lingers around the enclosed area. The same logic applies to infectious droplets in the air, according to the study. Indoors and when masked, factors besides distance can be more important to avoid transmission.
As for outdoor social distancing, Bazant says it makes almost no sense and that doing it with your masks on is “kind of crazy”.
“When you look at the flow of air outside, the infected air is swept away and is very unlikely to cause transmission. There are very few recorded cases of outdoor transmission.” he said. “Crowded outdoor spaces could be a problem, but if people keep a reasonable distance of about 3 feet outside, I feel pretty comfortable with it even without masks.”
According to Bazant, this could possibly explain why states like Texas or Florida, where companies reopened with no capacity constraints, had no transmission spikes.
For variant strains that are 60% more transmissible, increasing ventilation by 60%, reducing the time spent indoors, or limiting the number of people indoors could offset this risk.
Bazant also said a big question will be when to remove masks and that the study’s guidelines can help quantify the risks involved. He also noted that measuring carbon dioxide in a room can also help quantify how much infected air there is, and therefore the risk of transmission.
“We need scientific information that is conveyed to the public in a way that is not only frightening but actually based on analysis,” said Bazant. After three rounds of intense peer reviews, he said it was the most review he had ever been through and he hoped it will influence policy now that it is released.