With an aggressive new strain spreading across the country, this year's flu season has been marked by record-high hospitalizations and reportedly intense symptoms.
As people look for ways to contain the spread, new research has found that a few simple factors can greatly reduce transmission.
Researchers from the University of Maryland Schools of Public Health and Engineering in College Park and the School of Medicine in Baltimore studied influenza spread by placing flu-positive college students in a hotel room with healthy middle-aged adult volunteers.
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The study, published in the journal PLOS Pathogens, is reportedly the first clinical trial investigating how the flu spreads from naturally infected people to uninfected people, according to a press release.
The participants, including 11 healthy volunteers, lived on a quarantined floor of a Baltimore-area hotel for two weeks. During that time, they simulated interactions, including having conversations, doing physical activities like yoga, and passing around objects like pens and tablets from infected people to the rest of the group.
Researchers monitored the participant's symptoms, performed daily nasal swabs, and collected saliva and blood samples to test for antibodies, the release stated.
The study also measured the "viral exposure" in the volunteers' breathing air and ambient air in the activity room. The exhaled breath of the participants was measured by a machine called the Gesundheit II, invented by researcher Dr. Donald Milton and colleagues at Harvard T.H. Chan School of Public Health.
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At the end of the experiment, none of the healthy individuals had become infected with the flu due to a variety of factors. This included a lack of coughing, as the infected students were holding "a lot of virus in their noses" and only small amounts were "expelled into the air," the researchers noted.
"Our data suggests key things that increase the likelihood of flu transmission - coughing is a major one," Dr. Jianyu Lai, post-doctoral research scientist and the study's lead data analyst and report writer, shared in a statement.
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The other factor was ventilation and air movement, as the air in the study room was "continually mixed rapidly by a heater and dehumidifier, and so the small amounts of virus in the air were diluted," Lai pointed out.
The researcher added that middle-aged adults are "usually less susceptible" to influenza than younger adults.
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Most researchers assume that airborne transmission is a major factor of disease spread, according to Dr. Donald Milton, professor at SPH's Department of Global, Environmental and Occupational Health and a global infectious disease aerobiology expert.
"At this time of year, it seems like everyone is catching the flu virus, and yet our study showed no transmission," he said in the same press release. "What does this say about how flu spreads and how to stop outbreaks?"
Milton, who was reportedly among the first experts to identify how to stop the spread of COVID-19, noted that findings from these types of trials are essential to updating international infection-control guidelines.
"Being up close, face-to-face with other people indoors where the air isn't moving much, seems to be the most risky thing - and it's something we all tend to do a lot," he said.
"Our results suggest that portable air purifiers that stir up the air, as well as clean it, could be a big help," Milton suggested. "But if you are really close and someone is coughing, the best way to stay safe is to wear a mask, especially the N95."
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Approximately 11 million flu illnesses and about 5,000 deaths have occurred so far in the 2025-2026 influenza season, according to CDC data. A large share of the current flu cases are caused by the new influenza A subclade K variant.
