Joe Allen thinks about air a lot. Specifically, the air we breathe indoors.

For the Harvard professor, founder of the university’s Healthy Buildings Program, our building design and public health officials have ignored indoor air systems for too long – that is, until the COVID pandemic hit.

But by then, it was too late. That lack of attention contributed to tens of thousands of COVID cases, Allen says. He believes rethinking building design is crucial to preventing the spread of COVID and other potentially deadly respiratory infections in the future.

“Think about the public health gains we’ve made over the past hundred years. We’ve made improvements to water quality, outdoor air pollution, our food safety; we’ve made improvements to sanitation: absolute basics of public health,” he said. “Where has indoor air been in that conversation? It’s totally forgotten about. And the pandemic showed what a glaring mistake that was.”

One of the earliest superspreaders

By March of 2020, COVID was spreading in the U.S.

That month, the Skagit Valley Chorale choir met at a church in Washington for rehearsal. Half the choir members showed up, including board members Debbie Amos and Coizie Bettinger.

“We just thought hand sanitizer, wash your hands a lot, you know, don’t hug each other, because that’s touch,” Bettinger said.

None of it was good enough. Choir members began to fall ill within a few days. In all, COVID hit 53 of the 61 people in the church that night. Two of them, both in their 80s, died.

“If you look at the way we design and operate buildings–and I mean offices, schools, local coffee shop[s]–we haven’t designed for health.”

Skagit County health officials concluded that choir members had “an intense and prolonged exposure” to surfaces and possibly airborne particles called “aerosols” containing the virus.

The conclusion caught the attention of Virginia Tech professor Linsey Marr, who specializes in aerosol science. Even though the medical community was focused on droplets, surfaces and handwashing, Marr and fellow researchers strongly believed COVID was primarily an airborne disease.

Marr used a portable fogger to help explain how so many choir members could have gotten sick.

“When they’re singing, they are releasing virus particles into the air constantly,” she said.

The choir was at the church for more than two hours and, throughout that time, virus particles drifted around, reaching other people, she said.

“You can imagine that after that amount of time, the other people would’ve breathed in enough of them to get sick themselves,” Marr said.

As far as Marr knows, the building’s heating, ventilation and air conditioning unit was not running that night. Researchers suspect it most likely automatically turned off because the choir members generated enough heat on their own.

Understanding of building ventilation advances

The analysis of the likely superspreader event led to one of the most significant papers on the importance of ventilation published during the pandemic. Then, last year, a study in Italy went further. It found that by using a school’s fans and air ducts to exchange indoor air with outdoor air five times per hour, the risk of COVID infections decreased by at least 80%.

In the U.S., it took until this past May for the Centers for Disease Control and Prevention to recommend an air exchange rate at all.

“If you look at the way we design and operate buildings–and I mean offices, schools, local coffee shop[s]–we haven’t designed for health,” Allen said. “We have bare minimum standards.”

Improving the level of filtration in a building is an easy and cheap change that can do more than just protect against COVID. It can also cut down on flu cases and protect against wildfire smoke, outdoor pollution and allergens, according to Allen.

Some companies are now focusing on indoor air for the health of their workers, as well as the health of their bottom lines.

“COVID shifted everybody’s mindset in terms of air quality, in terms of communicable or infectious diseases.”

Allen diagnoses problems in air quality systems and comes up with solutions for clients, including CBS parent company Paramount. He’s also worked with commercial real estate company Beacon Capital Partners and Amazon. Allen advised Amazon before it opened a 22-story office building in Arlington, Virginia, last May.

The top floor of Amazon’s new offices is a maze of pipes and air ducts. It’s part of a $2.5 million HVAC system that begins with massive rooftop vents and dampers.

“COVID shifted everybody’s mindset in terms of air quality, in terms of communicable or infectious diseases,” Katie Hughes, Amazon’s director of health and safety, said.

JPMorgan Chase says its new headquarters in New York City will have state-of-the-art air quality controls. Another New York City skyscraper, One Vanderbilt, already runs a modern HVAC system.

Having “healthy” buildings could bring workers from their homes back into offices, Allen said.

“All else equal, which building are you gonna go to? You have your choice right now: This building that put in healthy building controls, or this building that’s designed the way we’ve always designed buildings, and is prone to being a sick building?” Allen said.

Learning lessons

It’s not just companies changing. Skagit Valley Chorale rehearsals are now held in a different church with a new HVAC system. Doors stay open to let in fresh air, regardless of the season. There are even portable carbon dioxide monitors to track ventilation. Board member Debbie Amos said they’ve learned lessons from the aerosol study after the choir’s traumatic experience.

“Now we’re moving on in a way that we can still sing, but in a more safe manner,” she said.

As new strains of COVID continue to crop up and with flu season just getting started, Allen isn’t worried about people forgetting the importance of building air systems. He sees fundamental shifts in the scientific and medical communities, with companies taking note of what building design means for their employees’ health.

“I don’t think we’re gonna forget these lessons,” Allen said. “We better not.”

Originally published in CBS News.