-
In a new study, researchers had five people infected with the flu mingle with 11 people who did not have the virus in a hotel room with limited ventilation but a high rate of air recirculation.
-
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.
-
Doctors say this suggests that keeping air circulating and wearing an N95 mask could be helpful in preventing the spread of the flu.
A common tip for reducing the risk of flu is to avoid being around people who are obviously sick. But scientists recently did the opposite, putting people who had the flu in the same room as healthy participants as part of a small new study. (All participants provided written informed consent before enrolling in the study and retained the right to withdraw at any time.)
Shockingly, no one was infected.
“Our goal in this study was not to prevent influenza,” 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’ve been trying to understand how transmission happens so we can design better ways to prevent it from happening.”
Milton points out that about eight percent of people get the flu during a normal respiratory virus season, making it a pretty 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 takeaways for flu prevention, whether someone in your household has the virus or you just want to be safe.
Meet the experts: Amesh A. Adalja, MD, is an infectious disease expert and principal investigator 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 co-author of the study and a professor in the Department of Global, Environmental, and Occupational Health at the University of Maryland School of Public Health.
What did the study find?
For PLOS pathogens In the study, the researchers had five people infected with the flu mix with 11 people who did not have the virus in a hotel room with limited ventilation but a high rate of air recirculation.
Study participants lived on an isolated hotel floor for two weeks and did daily routines that were designed to mimic real-life social interactions, such as casual conversation, yoga, stretching and dancing. People who were infected touched things like a pen, tablet and microphone, 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 the levels of the virus in the participants’ air and breath.
Ultimately, none of the healthy participants got sick.
Why didn’t everyone get infected?
There are probably a few reasons for this. “Most people would find it shocking to realize that every time scientists have tried to put people in a room to see if infected people would infect uninfected people with the flu, it hasn’t worked,” says Dr Milton. “It’s weird.”
His team guessed that this was because previous studies used laboratory viruses that had circulated years ago (and to which people had built up an immunity), which is why they decided to use people who were naturally infected with current strains of the virus.
But Dr. Milton believes one reason the healthy participants didn’t get sick is that they were middle-aged adults who had years of exposure to the flu. As a result, they may have more natural immunity than younger people, he says.
The study was also done during a milder flu year (2023-2024), meaning not this year, Dr. Milton points out. While many of the study participants had high levels of the flu virus in their noses, they did not have a cough. “In previous years, we’ve seen that people who don’t cough don’t clear much of the virus,” he says. “Flu cases where people cough are the most contagious.”
Dr Milton says the ventilation was “intentionally pretty bad”, with researchers sealing the doors and doing everything they could to limit ventilation. But the air also moved a lot around the room. “We wanted to have a well-mixed environment, thinking it would expose everyone,” he says. “It turned out that it worked the other way around. There was enough air in the room that when you had people who weren’t coughing a lot, everyone was exposed to a small amount of the virus, which wasn’t enough.”
What is the result of staying well?
Doctors say there are a few things you can do with this information, whether you’re out in public or someone in your home is sick. Limiting coughing — by using cough suppressants or having the sick person wear a mask around others — can be helpful, according to Amesh A. Adalja, MD, an infectious disease expert and senior researcher at the Johns Hopkins Center for Health Security.
“Coughing is a major mechanism by which viral particles spread through the air,” he explains. “Decreasing coughing decreases 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 usually hard to open the windows in the winter because of the cold, and the air inside is pretty thin,” he says. “But it’s a reasonable idea to use an air filter in the home.” Running 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 individual,” he says.
But one of the best ways to protect yourself is to wear an N95 mask, especially if you’re around people who are coughing, says Dr. Milton. “In the end, all these layers of protection work – this shows it,” he says.
You may also like