Photo: Tony Rinaldo

The research laid bare what a growing number of scientists who studied indoor air believed: aerosol transmission of COVID-19 was not just possible, but was likely a key transmitter of the SARS-CoV-2 virus.

Among them was Parham Azimi (Ph.D. ENVE ’16), a research fellow at the Harvard T. H. Chan School of Public Health, who led a team of scientists whose study of COVID-19 transmission on a cruise ship was among the first to show that aerosol transmission was a concern that needed to be taken seriously.

Public health organizations such as the Centers for Disease Control and Prevention and the World Health Organization pushed back at the notion of aerosol transmission, only begrudgingly acknowledging its possibility after more than 200 scientists, including two of Azimi's mentors, argued for it in a letter to the WHO and as more research, including that done by Azimi's team, poured in about its reality.

Never expecting to spend his career researching infectious diseases, Azimi found himself frustrated by the pushback. Settling into this career field, one focused on educating the public to help them stay safe, he saw the two public health organizations diluting the message.

“[The public] really cares about their health,” Azimi says. “I saw that [schools and restaurants he consulted for] wanted to have a healthier environment. They were cleaning surfaces every hour. And they were injecting disinfectants into the air. They didn’t know that the right way to do it is increasing ventilation.”

Azimi began his infectious disease transmission research as Illinois Tech Professor of Architectural Engineering Brent Stephens’s first doctoral student in 2012, with a project studying the impact of HVAC filters on limiting the risk of influenza transmission in indoor environments. It continued at T. H. Chan, where one of his early projects focused on finding a way to control the 2019 outbreak of measles among children. His experiences modeling the transmission of infectious diseases proved indispensable when the potential enormity of COVID-19’s impact started to hit home in January 2020.

A member of the research team led by Joseph Allen, an associate professor of exposure assessment science at T. H. Chan and director of the Harvard Healthy Buildings Program, Azimi was tasked with studying COVID-19 transmission. The team, which included Stephens and Azimi’s wife, Zahra Keshavarz, among others, recognized the importance of studying a controlled environment. The COVID-19 crisis aboard the Diamond Princess cruise ship in Japan (where one infected passenger turned into more than 700 infected) in early 2020 immediately jumped to mind.

“We knew that it was just one infector,” Azimi says of the outbreak on the vessel. “We knew how many days he was there. And then, approximately, we knew how people interacted on that cruise ship and how many people got infected during that time. We used that case study to be able to estimate the contribution of different pathways in transmission of COVID-19.”

Azimi says the initial plan was to run 12 scenarios, but they ended up running more than 20,000. The results showed that aerosol transmission—small droplets that hang in the air—likely accounted for more than 50 percent of the COVID-19 transmission on the Diamond Princess.

“Now that we have a COVID vaccine, what happens in 10 years?”—PARHAM AZIMI

Azimi’s modeling programs allowed scenarios to simultaneously look for transmission through droplets and aerosols, transmission beyond six feet, and transmission through contaminated surfaces. Most modeling programs look solely at airborne transmission, Allen says. The research brought the idea of aerosol transmission of COVID-19 to the public and was noteworthy enough to earn publication in the New York Times in late July 2020, well before its publication in the Proceedings of the National Academy of Sciences in February 2021.

“The modeling work is really quite sophisticated, and it is a credit to Parham’s skill,” Allen says. “The real power of the model is for what it can become. Yes, we were interested in understanding the disease dynamics on the Diamond Princess, but it's a model that can be used for other infectious disease models going forward.”

That's what drives Azimi, helping to keep the public safe from infectious diseases like COVID-19. He wants them to understand that they simply can't wait for a vaccine; they have to understand the importance of indoor air and ventilation. It's the only way to prepare for whatever comes next.

“I'm a member of the ASHRAE Epidemic Task Force, with a focus on ventilation. We wanted to suggest what is the required or desired ventilation for indoor environments,” he says. “We are working on that, too, making suggestions to homeowners and building managers to tell them know how they can find out if their building is safe. Is it reducing the number of the people that are there or increasing the ventilation? What are the mitigation techniques that they are taking and how it would be help them to reduce the risk?”

Azimi adds, driving home the point: “We had a measles vaccine, and the influenza vaccine is safe and cost effective, but there are outbreaks of that….Now that we have a COVID vaccine, what happens in 10 years? If we have another disease, are we ready for that? We have to make our buildings and built environments ready for another pandemic.”