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In a new study, researchers matched five people infected with the flu in a hotel room with limited ventilation, but with 11 people with high air recirculation rates.
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Ultimately, none of the healthy participants got sick, which could be due to the participants’ age (and natural immunity to the flu), among other factors.
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Doctors recommend that keeping the air moving and wearing an N95 mask can help prevent the spread of the flu.
A common piece of advice to reduce your flu risk is to avoid being around people who are obviously sick. But scientists recently did the opposite, putting people with the flu in the same room as healthy participants as part of a small new study. (All participants provided written informed consent prior to enrollment in the study, and they retained the right to withdraw at any time.)
Surprisingly, no one was infected.
“Our goal in this study was not to prevent the flu,” says infectious disease aerobiology expert Donald Milton, MD, study co-author and professor in the Department of Global, Environmental and Occupational Health at the University of Maryland School of Public Health. “We were trying to understand how transmission happens so we can design better ways to stop it.”
Milton says that about eight percent of people get the flu during the season with a common respiratory virus, which makes it a highly contagious virus.
So…why didn’t healthy people get the flu, even when they were in the same room as the infected? The findings offer some key ways to prevent the flu, whether someone in your household has the virus or you want to play it safe.
Meet the experts: Amesh A. Adalja, MD, is an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security. Thomas Russo, MD, is professor and chief of infectious diseases at the University at Buffalo in New York. Infectious disease aerobiology expert Donald Milton, MD, is a study co-author and professor in the University of Maryland School of Public Health’s Department of Global, Environmental and Occupational Health.
What did the study find?
for the PLoS Pathogens In the study, researchers matched five people infected with the flu in a hotel room with limited ventilation, but with 11 people with high air recirculation rates.
Study participants sat on isolated hotel floors for two weeks and performed daily routines designed to mimic real-life social interactions such as casual conversation, yoga, stretching and dancing. Infected people touched things like pens, tablets and microphones, which were then passed around the group.
During this time, the researchers tracked the participants’ symptoms and collected daily data, such as nasal swabs, saliva and blood samples. They also measured levels of the virus in the air and in participants’ breath.
Ultimately, none of the healthy participants became ill.
Why not all infected?
There are probably a few reasons for this. Dr. “It’s surprising to most people every time scientists try to put infected people in a room to see if they infect other people with the flu,” says Dr. Milton. “It’s weird.”
His team speculated that this was because previous studies had used laboratory viruses that had been circulating years before (and people had built up immunity), so they decided to use people naturally infected with the current strain of the virus.
But Dr. One reason the healthy participants didn’t get sick, Milton said, was that they were middle-aged adults who had been exposed to the flu for years. As a result, they may have more natural immunity than younger people, he says.
The study was also conducted in a mild flu year (2023-2024), not this year, Dr. Milton pointed out. While many study participants had high levels of influenza virus in their noses, they did not develop a cough. “In past years, we’ve seen that people who don’t cough don’t shed much virus,” he says. “Flu cases where people cough are the most contagious.”
Dr. Milton says that since the ventilation was “objectively very poor,” researchers closed the doors and did everything they could to limit ventilation. But the wind was also moving around the room. “We wanted to have a nice mixed environment, thinking that everyone would be exposed,” he says. “It turned out that it did the opposite. There was enough air in the room that when you had people who didn’t have a lot of coughs, everyone was exposed to a small amount of the virus, which wasn’t enough.”
What’s the takeaway for staying well?
Doctors say there are things you can do with this information if you’re out in public or someone in your home is sick. According to Amesh A. Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, limiting coughing — using a cough suppressant or wearing a mask around others when sick — can be helpful.
“Coughing is a major mechanism by which viral particles are spread through the air,” he explains. “Coughing reduces the chance of spreading respiratory viruses.”
Good airflow is also helpful, says Thomas Russo, MD, professor and chief of infectious diseases at the University of Buffalo in New York. “It’s difficult to open windows in winter because the circulation of cold and indoor air is very low,” he says. “But using an air filter at home is a good idea.” Turning on ceiling fans can also help, Dr. Milton says. Dr. Adalja agrees. “The better the airflow, the less likely viral particles in the air will land on another person,” he says.
But the best way to protect yourself is to wear an N95 mask — especially if you’re around people who are coughing, says Dr. Milton. “Ultimately, all of these layers of protection work — that’s what it shows,” he says.
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