A new study published in the scientific journal Cell provides the clearest evidence to date that people infected with influenza actively expel infectious virus into the air and that the amount released varies enormously between individuals. Using a newly developed air-sampling system in a controlled human infection study, researchers captured live influenza virus directly from the air expelled by infected participants and traced its genetic diversity from the body into the environment.
The findings, published on March 19, 2026, help explain why some people appear far more likely than others to transmit respiratory viruses and offer new insight into how influenza spreads through the air.
“We’ve known influenza can be transmitted through the air, but directly capturing infectious virus from people and linking it to symptoms and viral load over time has been technically very difficult,” says Seema S. Lakdawala, PhD, senior author of the study, associate professor of microbiology and immunology at Emory University, and co-director of Emory Center for Transmission of Airborne Pathogens. “This study shows that some individuals release orders of magnitude of more infectious virus than others, suggesting a superspreader-like effect. It also shows that the amount of virus in the nose is not the best metric for predicting how much infectious virus is expelled into the air.”
An order of magnitude represents a 10-fold (or 10x) difference in size or quantity.
Overcoming a long-standing technical barrier
Detecting infectious viruses in the air has been a major challenge in respiratory virus research. Many air-sampling tools can detect viral RNA but they often damage viruses during collection, making it impossible to determine whether the captured virus can still infect another person.
The team’s Modular Influenza Sampling Tunnel (MIST) collects respiratory particles in a way that preserves infectivity by allowing particles to settle directly onto living cells. Culture plates with cells line the base of a 3 ft long tunnel, and as aerosols travel through the tunnel they will fall at varying distances onto the cells. This approach enables researchers to culture, quantify and sequence infectious virus across a wide range of particle sizes.
“Measuring infectious virus in the air is incredibly challenging,” says Linsey C. Marr, PhD, co-senior author of the study and professor of civil and environmental engineering at Virginia Tech. “Existing methods are good at counting particles or detecting viral genetic material, but they don’t preserve virus infectivity. We designed our sampling method to bridge that gap so we can connect what people are exhaling with the ability to transmit an infection.”
Controlled human infection study links symptoms, viral dynamics and infectious aerosols
The study used a controlled human influenza infection model, allowing researchers to precisely track viral loads, symptoms and airborne shedding over time, something that is nearly extremely difficult to do in natural infections.
“Human challenge studies provide a unique window into how infections unfold in real people, day by day,” says Nadine G. Rouphael, MD, clinical principal investigator of the study and director of the Hope Clinic at Emory University, the clinical arm of the Emory Vaccine Center. “This approach allows us to safely and carefully link symptoms, viral dynamics and transmission-relevant outcomes in ways that directly inform public health.” Rouphael is also a professor of vaccinology and infectious diseases at Emory University.
Participants were closely monitored in a specialized hospital clinical trials unit, enabling repeated air sampling during speaking, coughing and sneezing across multiple days of infection.
Key findings
The researchers observed striking differences in how much infectious virus participants released into the air. Some expelled little to no detectable infectious virus, while others released levels that differed by more than three orders of magnitude.
The infectious virus expelled into the air correlated strongest with symptom severity including congestion, fatigue and body aches. While coughing and sneezing generally released more virus than speaking, individual differences were the dominant driver of infectious aerosol output.
By sequencing virus recovered from airborne particles and comparing it with virus sampled from the nose and mouth, the team found that multiple viral genetic variants were present in expelled infectious aerosols.
“We were surprised by how much viral diversity was maintained in the particles people expelled,” says Anice C. Lowen, PhD, co-senior author of the study, professor of microbiology and immunology at Emory University, and co-director of Emory Center for Transmission of Airborne Pathogens. “This tells us that the tight genetic bottlenecks seen during transmission don’t happen when virus leaves the body—they occur later, during exposure of a new host.”
Why it matters
Together, the findings help explain why influenza transmission can be highly uneven, with a small number of individuals potentially driving a disproportionate share of spread. By directly linking symptoms, viral load and infectious aerosols, the study provides a foundation for evaluating interventions such as ventilation, masking and air disinfection.
The MIST platform can also be adapted to study other respiratory viruses, including emerging pathogens.
This work was supported, in whole or in part, by Flu Lab, NIAID CEIRR 75N93021C00017, P01AI186819.
Learn more about the Emory Center for Transmission of Airborne Pathogens at www.ctap.emory.edu