Songs for Science

Last August, more than 1,400 people crowded into a stadium in Leipzig, Germany, for a live concert. But they weren’t just there to dance, clap, and listen to a local pop band. They were also there for science. Researchers staged the event to test how the virus that causes Covid-19 might spread at a large public gathering, based on different levels of social distancing. They wanted to investigate whether it’s possible to hold these events safely.

Concert attendees volunteered to take part in the study. To reduce the risk of transmission during the study, the scientists tested each concertgoer before the show to make sure they didn’t have Covid-19. The volunteers were also required to wear N-95 masks, which offer the highest level of protection to wearers so they don’t breathe in virus particles.

In addition to masks, the study participants wore tracking devices that monitored their location as they listened to catchy tunes, wandered the aisles, and waited in line for snacks. The scientists wanted to know how close concertgoers actually came to one another, even when told to social distance, and how that affected their chances of catching Covid-19.  

When people talk, breathe, and sneeze, they spray tiny droplets of water, mucus, and saliva into the air. At large events like concerts, these aerosols could expose dozens of people to airborne diseases, such as Covid-19.

Aerosols can also build up in the air, making live concerts held indoors particulary high-risk, says Dr. John Townes. He’s an infectious disease specialist at Oregon Health and Sciences University, who was not involved in the study. “If you have a person who is singing, shouting, talking, and laughing, that means they’re producing more aerosols,” he explains. That increased risk is the reason most concert venues were shutdown at the start of the pandemic (see “The Future of Concerts?” in Science World’s December 14, 2020, issue).

To simulate the spread of aerosols, the researchers in Germany set up smoke machines to blow fog into the audience. Then they had people attend three different concerts, each with a different level of social distancing: at one, guests were told to stay spaced 2.7 meters (9 feet) apart, at another they were placed in a checkerboard seating arrangement, and in the the third they were tightly packed together. Later, the researchers used a computer to estimate the number of people exposed to the fog under these conditions.

The researchers found that when told to stay 2.7 m (9 ft) apart, most participants came within 1.5 m (5 ft) of each other fewer than 20 times. And usually, they didn’t stay close for more than 15 minutes, which makes it less likely that they would spread the virus if they’d been sick with Covid-19.

The researchers also discovered the importance of ventilation—the flow of fresh air in and out of a space. When powerful jets propelled fresh air towards the floor of the stadium, computer models estimated no more than one person would be exposed to infected aerosols for each person in the audience with Covid-19, as long as participants stayed socially distanced by at least 2.7 meters (9 ft). Without the jets, 10 times as many people were exposed. “Ventilation is key,” says Townes. “If you have a large event, as long as you keep air flowing and people spread out, you’re not going to have as much transmission between people.”

The results of the study suggest that cities with few cases of Covid-19 might safely hold events in the future—with the right set up and strict social distancing, says Dr. Stefan Moritz, an infectious disease expert from University Hospital of Halle in Germany who led the study. “From our point of view, the experiment was an absolute success,” he adds. 

Holding a concert during a pandemic might work in an experimental setting because the study volunteers agreed to take necessary precautions and follow the researchers’ instructions, like wearing masks and social distancing. “At an actual concert, though, it would be difficult to make sure everyone was on the same page about safety,” says Townes. “It doesn’t work unless everyone follows the rules.” So despite the seemingly optimistic results of the study, it will be a while before officials declare it’s safe to attend concerts or cheer on sports teams in person without risking a spike in Covid-19 cases.

But new developments may help life return to normal soon. In December, vaccines created by the drug companies Pfizer-BioNTech and Moderna received emergency authorization from the U.S. Food and Drug Administration (see “U.S. Authorizes First Vaccine for Covid-19”). The vaccines are currently being distributed to high-risk health-care workers and those in longterm care facilities. The rollout process will continue well into 2021—and until the majority of people are vaccinated, large gatherings will still be risky. “The more people you get together, the greater the chance of transmission,” Townes says. “By keeping your distance, you’re not just keeping yourself safe. You’re keeping your friends and their families safe too.”